🧪 Chapter 2 · NCERT Science IX

IS MATTER AROUND
US PURE?

Unravel the classification of matter — pure substances vs mixtures, homogeneous vs heterogeneous, and the elegant art of separation.

2Pure Types
6+Sep. Methods
5 hrsStudy Time
★★★★Exam Weight
📍 Chapter Snapshot
📖Chapter 02
⏱️Est. Study Time: 5 hrs
🎯Difficulty: Moderate-Hard
🔬Type: Chemistry
Matter
Pure Substance
Mixture
Element
Compound
Homogeneous
Heterogeneous
Metal / Non-metal / Metalloid
Fixed ratio of elements
Solutions / Alloys
Colloids / Suspensions
🎯 Why This Chapter Matters for Exams
📌 Colloidal solutions and Tyndall Effect are highly tested 2–3 mark questions.
📌 Differences between compounds and mixtures come every year — prepare a table.
📌 Separation methods (distillation, chromatography) often carry 3–5 marks with diagrams.
📌 Alloys and solutions are popular in MCQ rounds of Olympiads and NTSE.
💡 Key Concept Highlights
Tyndall EffectColloidSuspensionSolutionSolubilityDistillationChromatographyCentrifugationCrystallisationAlloyElementCompound
⚗️ Important Formula Capsules
Mass/Vol Percent(mass of solute / mass of soln) × 100
Vol/Vol Percent(vol of solute / vol of soln) × 100
Solubilitymass dissolved / 100 g solventg
📚 What You Will Learn
  • 1Difference between pure substances and mixtures with real-life examples
  • 2Properties and types of solutions, colloids, and suspensions
  • 3Separation techniques and when to apply each method
  • 4How to distinguish elements from compounds experimentally
  • 5Practical applications — desalination, fractional distillation of air
🔗 Navigate to Chapter Resources
📄
Full Notes
🧩
MCQs Practice
✅
True / False
📝
NCERT Exercises
🏆 Exam Strategy & Preparation Tips
01
Make a Table
Prepare a 4-column comparison: Solution | Colloid | Suspension | Compound.
02
Tyndall Effect
Always explain Tyndall Effect with a diagram and example (milk, fog, smoke).
03
Lab Setup Diagrams
Distillation and chromatography apparatus diagrams fetch easy marks — practise them.
04
Application Focus
Link concepts to daily life: salt water (solution), milk (colloid), muddy water (suspension).
Chapter 1 · CBSE · Class IX
⚗️

Pure Substance

NCERT Class 9 Science Matter Is Matter Around Us Pure Pure Substances Mixtures Elements Compounds Solutions Suspensions Colloids Homogeneous Mixtures Heterogeneous Mixtures Separation of Mixtures Filtration Evaporation Centrifugation Chromatography Distillation Separating Funnel Air Pollution Types of Solutions Tyndall Effect
📋
Table of Contents
13 sections
🗺️ Overview
pure substance

A pure substance is a form of matter that consists of only one kind of particles and has a fixed chemical composition throughout its mass. The particles present may be atoms, molecules, or ions, but every particle is chemically identical to the others.

Pure substances possess characteristic properties such as fixed melting point, fixed boiling point, definite density, and specific chemical behavior. Because of these constant properties, pure substances can be identified and distinguished from mixtures.

🗒️ pure substance
pure substance

A substance containing only one type of constituent particles and having a uniform composition throughout is called a pure substance.

🔷 Characteristics
Characteristics of Pure Substances
🔷 Characteristics of Pure Substances
  • Made up of only one type of particles.
  • Have a fixed and definite composition.
  • Possess uniform properties throughout the sample.
  • Cannot be separated into simpler substances by physical methods.
  • Have fixed melting and boiling points.
  • Exhibit characteristic physical and chemical properties.
  • May exist as elements or compounds.
💡 Concept Builder
🗂️ Types of Pure Substances
Elements
  • Contain only one kind of atom.
  • Cannot be broken into simpler substances by chemical reactions.
  • Examples: Iron (Fe), Gold (Au), Oxygen (O₂), Copper (Cu).
Compound
  • Formed by chemical combination of two or more elements in a fixed ratio.
  • Can be decomposed into constituent elements by chemical methods.
  • Examples: Water (H₂O), Carbon Dioxide (CO₂), Sodium Chloride (NaCl).
📊 Pure Substance vs Mixture
Property Pure Substance Mixture
Composition Fixed and definite Variable
Types of Particles Only one type Two or more types
Melting Point Fixed Not fixed
Boiling Point Fixed Occurs over a range
Separation Cannot be separated by physical methods Can be separated by physical methods
🌟 Why Are Pure Substances Important?
✏️ Example
Material Pure Substance or Not? Reason
Distilled Water Pure Substance Contains only H₂O molecules
Gold (24 Carat) Pure Substance Contains only gold atoms
Oxygen Gas Pure Substance Contains only oxygen molecules
Milk Not Pure Contains many substances
Air Not Pure Mixture of gases
Sea Water Not Pure Contains dissolved salts and minerals
🎨 SVG Diagram
Pure Substance vs. Mixture
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 Pure Substance 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 All particles are chemically identical 51 52 53 54 55 56 Mixture 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 Physically blended distinct particles 74 75

In a pure substance, every particle is chemically identical. This uniformity gives rise to fixed physical properties.

✏️ Solved Examples
Is oxygen a pure substance?
Yes. Oxygen contains only oxygen molecules (O₂). Since only one type of particle is present, it is a pure substance.
Why is milk not considered a pure substance?
Milk is a mixture of water, fats, proteins, and other components. Since it contains multiple types of particles, it is not a pure substance.
⚡ Exam Tip
❌ Common Mistakes
  • Writing that only elements are pure substances.
  • Considering milk as a pure substance because it appears uniform.
  • Confusing homogeneous mixtures with pure substances.
  • Ignoring the importance of fixed composition.
  • Thinking that a pure substance must contain only one atom.
📋 Case Study
CBSE Competency-Based Question (HOTS)

A student observes two transparent liquids. One is distilled water and the other is a salt solution. Both appear identical.

Which one is a pure substance and why?

Answer:

Distilled water is a pure substance because it contains only H₂O molecules. Salt solution contains water and dissolved salt particles; therefore, it is a mixture.

⚡ Quick Revision
  1. Definition of pure substance.
  2. Fixed composition.
  3. Uniform properties.
  4. Types: Elements and Compounds.
  5. Difference between pure substance and mixture.
  6. Examples from daily life.
  7. CBSE conceptual questions.
⚗️

Mixture

📋
Table of Contents
15 sections
🗺️ Overview

A mixture is a physical combination of two or more pure substances present in any proportion. The substances forming a mixture do not undergo any chemical change and retain their individual properties.

Mixtures are constituted by more than one kind of pure form of matter. Since no new substance is formed, the components of a mixture can usually be separated by suitable physical methods.

📘 Definition
🔷 Characteristics of Mixtures
🔷 Characteristics
  • Made up of two or more substances.
  • Components retain their original properties.
  • No new substance is formed.
  • Composition is not fixed.
  • Can be separated by physical methods.
  • May be homogeneous or heterogeneous.
  • Do not have fixed melting and boiling points.
  • The components may be present in any proportion.
🗒️ Why Study Mixtures?

Most materials around us are mixtures rather than pure substances. Air, soil, seawater, milk, blood, alloys, beverages, medicines, and fuels are all mixtures.

Understanding mixtures helps us learn various separation techniques such as filtration, evaporation, distillation, centrifugation, sublimation, and chromatography.

🗂️ Types of Mixtures
Homogeneous Mixtures Heterogeneous Mixtures
Homogeneous Mixtures
A mixture which has a uniform composition throughout is called a homogeneous mixture. Such mixtures are also known as solutions.
In a homogeneous mixture, the components are evenly distributed and cannot be distinguished with the naked eye.

Characteristics of Homogeneous Mixtures
  • Uniform composition throughout
  • Only one phase is visible
  • No visible boundaries between components
  • Particles are evenly distributed
  • Appear as a single substance
Examples
  • Salt dissolved in water
  • Sugar solution
  • Air
  • Vinegar
  • Brass (alloy of copper and zinc)
Heterogeneous Mixtures
Mixtures which contain physically distinct parts and have non-uniform composition are called heterogeneous mixtures.
In such mixtures, different components can often be seen separately.

Characteristics of Heterogeneous Mixtures
  • Non-uniform composition
  • Two or more phases may be present
  • Visible boundaries exist between components
  • Components remain physically distinct
  • Composition varies from one region to another
Examples
  • Sand and water
  • Oil and water
  • Soil
  • Granite
  • Mixture of iron filings and sulphur
📊 Comparison Table

Difference Between Homogeneous and Heterogeneous Mixtures

Difference Between Homogeneous and Heterogeneous Mixtures
Homogeneous Mixtures Heterogeneous Mixtures
Uniform composition throughout. Non-uniform composition.
Only one phase is visible. Two or more phases may be visible.
No visible boundaries. Visible boundaries are present.
Components are evenly distributed. Components are unevenly distributed.
Generally appear as a single substance. Different substances can often be identified.
Example: Salt solution. Example: Sand in water.
Air Oil and water
Brass Soil
Vinegar Granite
📌 Particle-Level Understanding
🎨 SVG Diagram
Particle Distribution in Mixtures
9 15 21 31 34 Homogeneous Mixture 39 47 52 Uniform composition throughout 60 Heterogeneous Mixture 65 75 Distinct regions of different particles

The left box shows uniform distribution of particles, whereas the right box shows clustering of different particles into separate regions.

📊 Difference Between Pure Substance and Mixture
Pure Substance Mixture
Contains only one type of substance. Contains two or more substances.
Fixed composition Variable composition
Fixed melting and boiling points. No fixed melting or boiling point.
Cannot be separated by physical methods. Can be separated by physical methods.
Uniform properties throughout. Components retain their own properties.
Examples: Gold, Oxygen, Water Examples: Air, Milk, Soil
🗒️ Applications of Mixtures in Daily Life
  • Air supports life and combustion.
  • Alloys improve strength and durability of metals.
  • Medicines are often mixtures of several chemicals.
  • Food products contain mixtures of nutrients.
  • Fuels such as petrol and diesel are mixtures of hydrocarbons.
✏️ Example
Solved Example
Is air a homogeneous or heterogeneous mixture?
Air is a homogeneous mixture because gases such as nitrogen, oxygen, carbon dioxide, and argon are uniformly mixed.
Why is oil and water considered a heterogeneous mixture?
Oil and water do not mix uniformly and form separate layers. Hence, the composition is non-uniform.
⚡ Exam Tip
❌ Common Mistakes
  • Assuming homogeneous mixtures are pure substances.
  • Considering milk a pure substance.
  • Writing that mixtures have fixed composition.
  • Confusing solutions with compounds.
  • Thinking all mixtures can be separated by a single method.
📋 Case Study

A student is given three samples: air, soil, and salt solution. He is asked to classify them as homogeneous or heterogeneous mixtures.

Answer:

  • Air → Homogeneous mixture.
  • Salt solution → Homogeneous mixture.
  • Soil → Heterogeneous mixture.

Soil contains visibly different particles and therefore has a non-uniform composition.

🗒️ HOTS Question

Two beakers contain equal amounts of water. Sugar is dissolved in one beaker and sand is mixed in the other. Which mixture is homogeneous and why?

Answer:

Sugar solution is homogeneous because sugar particles are uniformly distributed throughout the water. Sand and water form a heterogeneous mixture because sand particles remain distinct and settle down on standing.

⚡ Quick Revision
  1. Definition of mixture.
  2. Characteristics of mixtures.
  3. Homogeneous mixtures.
  4. Heterogeneous mixtures.
  5. Comparison between the two types.
  6. Difference between mixture and pure substance.
  7. Examples and CBSE competency questions.
⚗️

Difference Between Pure Substance and Mixture

📋
Table of Contents
12 sections
📖 Introduction
💡 Concept
⚖️ Detailed Comparison
Pure Substance Mixture
Consists of only one type of constituent particles. Consists of two or more pure substances.
Has a fixed and definite composition. Has variable composition.
Contains identical particles throughout. Contains different types of particles.
Cannot be separated into simpler substances by physical methods. Can be separated into components by physical methods.
Possesses its own characteristic properties. Shows the properties of its components.
Has fixed melting and boiling points. Usually melts and boils over a range of temperatures.
Always homogeneous in composition. May be homogeneous or heterogeneous.
Represented by a definite chemical formula. No fixed chemical formula.
Examples: Gold, Oxygen, Water, Carbon Dioxide. Examples: Air, Milk, Soil, Salt Solution.
ℹ️ Particle-Level Understanding
🗒️ Information
In a pure substance, all particles are identical. In a mixture, different kinds of particles exist together without undergoing a chemical change.
Pure Substance One type of particle only Mixture Different particles together
✏️ Examples and Classification
Material Classification Reason
Distilled Water Pure Substance Contains only H₂O molecules.
Oxygen Gas Pure Substance Contains only oxygen molecules.
Gold Pure Substance Contains only gold atoms.
Air Mixture Contains several gases.
Milk Mixture Contains water, fats, proteins, and minerals.
Sea Water Mixture Contains water and dissolved salts.
🔤 Mnemonic
Quick Memory Trick
✏️ Example
Solved Example
A student is given a sample of air. Is it a pure substance or a mixture? Give a reason.
Air is a mixture because it contains several different gases (like nitrogen, oxygen, carbon dioxide, etc.) mixed together.
🗒️ CBSE HOTS Question
CBSE HOTS Question
A bottle contains distilled water while another bottle contains mineral water. Both are colourless and transparent.
Which one is a pure substance? Explain.
Answer: Distilled water is a pure substance because it contains only water molecules. Mineral water contains dissolved salts and minerals; therefore, it is a mixture.

📋 Case Study
CBSE Competency-Based Case Study

A laboratory technician receives three samples: oxygen gas, salt solution, and copper sulphate crystals. He needs to identify which are pure substances.

Answer:

  • Oxygen gas → Pure substance.
  • Copper sulphate crystals → Pure substance.
  • Salt solution → Mixture.

Oxygen and copper sulphate have fixed compositions, whereas salt solution can have varying amounts of salt and water.

❌ Common Mistakes
  • Thinking homogeneous mixtures are pure substances.
  • Assuming transparent substances are always pure.
  • Ignoring fixed composition while defining pure substances.
  • Writing that mixtures have definite chemical formulae.
  • Confusing compounds with mixtures.
⚡ Exam Tip
⚡ Quick Revision
  • Pure substance → One type of particle.
  • Mixture → Two or more substances.
  • Pure substance → Fixed composition.
  • Mixture → Variable composition.
  • Pure substance → Fixed melting and boiling points.
  • Mixture → Melting and boiling occur over a range.
  • Pure substance → Cannot be separated physically.
  • Mixture → Can be separated physically.
⚗️

Solution

📋
Table of Contents
15 sections
📘 Definition
🗂️ Components of a Solution
Solvent
The component present in a larger amount in a solution is called the solvent.
The solvent determines the physical state of the solution.
Examples
  • In salt water, water is the solvent.
  • In sugar solution, water is the solvent.
  • In air, nitrogen acts as the solvent because it is present in the largest amount.
Solute
The substance that dissolves in the solvent is called the solute.
The solute is generally present in a smaller amount than the solvent.
Examples
  • Salt is the solute in salt solution.
  • Sugar is the solute in sugar solution.
  • Carbon dioxide is the solute in aerated drinks.
💡 Concept Builder
🏷️ Properties of Solutions
Properties
Nature of Solution
A solution is a homogeneous mixture.
Particle Size
Generally less than 1 nm (10-9 m).
Visibility
Solute particles cannot be seen with the naked eye.
Light Scattering
Particles do not scatter light — the path of light is not visible.
Settling
Particles do not settle on standing; solutions are stable.
Separability
Cannot be separated by ordinary filtration.
Uniformity
Remains uniform throughout volume.
🎨 Particle Representation of a Solution
Homogeneous Solution: Uniform Particle Distribution

In a true solution, solute particles are uniformly distributed among solvent particles, making the mixture appear completely uniform.

🗂️ Classification of Solutions Based on Amount of Solute
Unsaturated Solution
A solution that contains less solute than the maximum amount that can dissolve at a given temperature is called an unsaturated solution.
Such a solution can dissolve more solute without changing the temperature.
Example
If a small amount of sugar is dissolved in water and more sugar can still dissolve, the solution is unsaturated.
Saturated Solution
At a particular temperature, a solution that has dissolved as much solute as it is capable of dissolving is called a saturated solution.
Any additional solute added to a saturated solution remains undissolved.
Important Note
The amount of solute that can dissolve depends upon temperature. Therefore, saturation is always specified at a particular temperature.
Supersaturated Solution
A solution that contains more dissolved solute than a saturated solution at the same temperature is called a supersaturated solution.
Such solutions are unstable and excess solute may crystallize out on disturbance.
Although supersaturated solutions are not specifically emphasized in NCERT Class 9, understanding them helps in higher classes and competitive examinations.
🗒️ Solubility
Solubility
The maximum amount of solute that can dissolve in a given amount of solvent at a specified temperature is called the solubility of the solute.
Solubility is usually expressed as the number of grams of solute dissolved in 100 g of solvent.
Solubility varies with temperature; generally, it increases with an increase in temperature for solids and liquids, while it decreases for gases.
📘 Definition
Concentration of a Solution
📌 Concentration in Terms of Mass Percentage
✏️ Example
Solved Numerical
Calculate the mass percentage of salt in a solution containing 20 g salt and 180 g water.
  1. Mass of Solute (salt)
    \[= 20\; g\]
  2. Mass of Solvent (water)
    \[= 180\; g\]
  3. Mass of Solution
    \[= 20 + 180 = 200\; g\]
  4. Mass Percentage
    \[\frac{20}{200} \times 100 = 10\%\]
✏️ Example
Examples of Solutions
Solution Solvent Solute
Salt Water Water Salt
Sugar Solution Water Sugar
Air Nitrogen Oxygen and other gases
Vinegar Water Acetic Acid
Brass Copper Zinc
❌ Common Mistakes
  • Confusing homogeneous mixtures with pure substances.
  • Thinking all transparent liquids are pure substances.
  • Assuming filtration can separate dissolved salt from water.
  • Ignoring the importance of temperature in saturation.
  • Mixing up solvent and solute.
⚡ Exam Tip
📋 Case Study
CBSE HOTS Question

Two students prepare sugar solutions. One student dissolves 10 g sugar in 100 g water, while the other dissolves 50 g sugar in 100 g water.

Which solution is more concentrated?

Answer: The second solution is more concentrated because it contains more solute in the same amount of solvent.

📋 CBSE Competency-Based Question

A teacher passes a beam of light through salt solution. Students observe that the path of light is not visible.

Explain the observation.

Answer: The particles in a true solution are extremely small (less than 1 nm). They do not scatter light. Therefore, the path of light is not visible.

⚡ Quick Revision
  • Solution = Homogeneous mixture.
  • Solvent = Present in larger amount.
  • Solute = Dissolved substance.
  • Particle size less than 1 nm.
  • Does not scatter light.
  • Cannot be separated by filtration.
  • Saturated solution contains maximum dissolved solute.
  • Unsaturated solution can dissolve more solute.
  • Mass Percentage = (Mass of Solute / Mass of Solution) × 100.
⚗️

Concentration of a Solution

📋
Table of Contents
10 sections
📘 Definition
🗒️ Why Do We Measure Concentration?
  • To compare the strengths of different solutions.
  • To prepare medicines in correct proportions.
  • To manufacture chemicals and fertilizers.
  • To determine purity and composition.
  • To perform quantitative chemical calculations.
💡 Concept Builder
📌 Methods of Expressing Concentration
⚖️ Comparison of Different Concentration Expressions
Method Formula Common Use
Mass by Mass (% w/w) \(\frac{\text{Mass of Solute}}{\text{Mass of Solution}} \times 100\) Solid dissolved in liquid
Mass by Volume (% w/v) \(\frac{\text{Mass of Solute}}{\text{Volume of Solution}} \times 100\) Medicines and laboratory solutions
Volume by Volume (% v/v) \(\frac{\text{Volume of Solute}}{\text{Volume of Solution}} \times 100\) Liquid-liquid solutions
🎨 SVG Diagram
Understanding Concentration Visually
Understanding Concentration Visually Dilute Solution Low Solute density Concentrated Solution High Solute density Solute Solvent
✏️ Example
Important Solved Numericals
Calculate the mass percentage of a solution containing 15 g sugar dissolved in 85 g water.
  1. Mass of Solution
    \[\begin{aligned} m_{\text{solution}} &= m_{\text{sugar}} + m_{\text{water}} \\ &= 15 \, \text{g} + 85 \, \text{g} \\ &= 180 \, \text{g} \end{aligned}\]
  2. Mass Percentage
    \[\begin{aligned} &=\frac{15}{100} \times 100 &= 15\% \end{aligned}\]
Calculate the volume percentage of alcohol if 30 mL alcohol is present in 300 mL solution.
  1. Volume Percentage
    \[\begin{aligned} &=\frac{30}{300} \times 100 &= 10\% \end{aligned}\]
⚡ Exam Tip
❌ Common Mistakes
  • Using mass of solvent instead of mass of solution in the denominator.
  • Forgetting to multiply by 100.
  • Mixing mass units with volume units.
  • Using wrong concentration formula.
  • Ignoring units in numerical problems.
📋 CBSE Competency-Based Question

Two students prepare salt solutions. Student A dissolves 10 g salt in 100 g water, while Student B dissolves 25 g salt in 100 g water.

Which solution is more concentrated?

Answer: Student B's solution is more concentrated because it contains a greater amount of solute in the same amount of solvent.

⚡ Quick Revision
  • Concentration measures the amount of solute present.
  • Mass by Mass: \(\frac{\text{Mass of Solute}}{\text{Mass of Solution}} \times 100\)
  • Mass by Volume: \(\frac{\text{Mass of Solute}}{\text{Volume of Solution}} \times 100\)
  • Volume by Volume: \(\frac{\text{Volume of Solute}}{\text{Volume of Solution}} \times 100\)
  • Concentrated solutions contain more solute.
  • Dilute solutions contain less solute.
⚗️

Example 1

📋
Table of Contents
4 sections
❓ Question
A solution contains 50 g of sugar dissolved in 350 g of water. Calculate the concentration of the solution in terms of mass percentage.
💡 Concept
Concept of Mass Percentage
🧩 Solution
Part (a)
Given:
  • Mass of Sugar (Solute) = 50 g
  • Mass of Water (Solvent) = 350 g
Part (b)
Step-by-Step Solution
  1. Mass of Solute \[50\; gm\]
    Mass of Solvent \[350\; gm\]
Part (c)
calculate the mass of the solution:
  1. Mass of Solution = Mass of Solute + Mass of Solvent
    \[ \begin{aligned} &=50 + 350\\ &=400\,g \end{aligned} \]
  2. Now apply the mass percentage formula:
    \[ \begin{aligned} \text{Mass Percentage} &= \frac{\text{Mass of Solute}} {\text{Mass of Solution}} \times 100\\ &= \frac{50}{400} \times 100\\ &= \frac{1}{8} \times 100\\ &=12.5\% \end{aligned} \]
⚡ Exam Tip
⚗️

Example 2

📋
Table of Contents
7 sections
❓ Question
To prepare a saturated solution at 293 K, 36 g of sodium chloride (NaCl) is dissolved in 100 g of water. Calculate the concentration of the solution in terms of mass percentage.
💡 Concept
Concept Used
🧩 Solution
Part (a)
Given:
  • Mass of Sodium Chloride (Solute) = 36 g
  • Mass of Water (Solvent) = 100 g
  • Temperature = 293 K
Part (b)
Step-by-step Solution
  1. Calculate the total mass of the solution:
    \[ \begin{aligned} \text{Mass of Solution} = \text{Mass of Solute} + \text{Mass of Solvent}\\ &=36 + 100\\ &=136\,g \end{aligned} \]
  2. Substitute the values in the mass percentage formula:
    \[\begin{aligned}\text{Mass Percentage} = \frac{36}{136}\times 100\\26.47\%\end{aligned}\]
🔍 Interpretation of the Result
A concentration of 26.47% means that every 100 g of saturated solution contains approximately 26.47 g of sodium chloride.
Since the solution is saturated at 293 K, no additional sodium chloride can dissolve in the solution at this temperature under normal conditions.
⚡ Exam Tip
🗒️ CBSE Competency Based Question

A student adds another 5 g of sodium chloride to the above saturated solution at 293 K and stirs continuously. What will happen?

Answer:

The additional sodium chloride will remain undissolved because the solution has already reached its maximum dissolving capacity (saturation point) at 293 K.

⚡ Quick Revision
  • Mass of NaCl = 36 g
  • Mass of Water = 100 g
  • Mass of Solution = 136 g
  • Mass Percentage = \(\frac{36}{136}\times100\)
  • Concentration = 26.47%
  • Solution is saturated at 293 K.
⚗️

Suspension

📋
Table of Contents
14 sections
📘 Definition
💡 Concept Builder
🏷️ Properties
Properties of a Suspension
Properties
Type
Suspension is a heterogeneous mixture.
Visibility
The particles of a suspension can be seen with the naked eye.
Particle Size
The particle size is generally greater than 1000 nm.
Optical Property
The particles scatter a beam of light passing through the mixture.
Optical Effect
Therefore, the path of light becomes visible.
Stability
Suspension particles settle down when left undisturbed.
Stability
Suspensions are unstable mixtures.
Separation
The particles can be separated by filtration.
Uniformity
The composition is non-uniform throughout the mixture.
🎨 Particle Representation of a Suspension
Suspension: Particles settle down over time
✏️ Common Examples of Suspension
  • Chalk powder in water.
  • Muddy water.
  • Sand in water.
  • Flour mixed with water.
  • Dust particles suspended in air.
  • Milk of magnesia (medicinal suspension).
🤔 Did You Know?
Why Does a Suspension Scatter Light?
The particles of a suspension are sufficiently large to obstruct and scatter light rays. As a result, the path of a beam of light becomes visible when it passes through the suspension.
This phenomenon is similar to the scattering of sunlight by dust particles in a room.
📌 Separation of Suspension by Filtration
⚖️ Difference Between Solution and Suspension
Solution Suspension
Homogeneous mixture. Heterogeneous mixture.
Particles are not visible. Particles are visible.
Particle size less than 1 nm. Particle size generally greater than 1000 nm.
Does not scatter light. Scatters light.
Stable mixture. Unstable mixture.
Particles do not settle down. Particles settle down on standing.
Cannot be separated by filtration. Can be separated by filtration.
✏️ Example
Solved Example
Why is muddy water considered a suspension?
Muddy water contains large insoluble soil particles dispersed in water. These particles are visible, settle down on standing, and can be removed by filtration. Therefore, muddy water is a suspension.
🛠️ Applications of Suspensions
  • Medicinal suspensions are used for delivering drugs.
  • Wall paints contain suspended pigment particles.
  • Water purification plants remove suspended impurities by filtration and sedimentation.
  • Many cosmetic products contain suspended particles.
❌ Common Mistakes
  • Confusing suspensions with true solutions.
  • Writing that suspension particles dissolve completely.
  • Forgetting that suspension particles settle down.
  • Ignoring the heterogeneous nature of suspensions.
  • Assuming suspensions cannot be filtered.
⚡ Exam Tip
📋 CBSE Competency-Based Question

A student mixes chalk powder in water and observes that the mixture appears cloudy. After some time, the chalk settles at the bottom.

Identify the type of mixture and justify your answer.

Answer:

The mixture is a suspension because the particles are visible, settle down on standing, and can be separated by filtration.

🗒️ HOTS Question

Why can muddy water be purified by filtration whereas salt solution cannot?

Answer:

Muddy water contains large suspended particles that cannot pass through filter paper. Salt solution contains dissolved salt particles that are extremely small and pass through the pores of the filter paper.

⚡ Quick Revision
  • Suspension is a heterogeneous mixture.
  • Particles are visible to the naked eye.
  • Particle size is generally greater than 1000 nm.
  • Scatters light.
  • Particles settle down on standing.
  • Can be separated by filtration.
  • Examples: Muddy water, chalk-water mixture, sand in water.
⚗️

Colloidal Solution

📋
Table of Contents
15 sections
📘 Definition
💡 Concept Builder
🗂️ Components of a Colloid
Dispersed Phase
Definition
The solute-like phase consisting of colloidal particles that are distributed throughout a medium.

Also known as the internal phase. These particles are larger than molecules but small enough to remain suspended without settling quickly. They are uniformly distributed but not truly dissolved.
Examples
Fat globules in milk. Solid carbon particles in smoke. Gelatin particles in jelly. Starch grains in starch solution.
note Particle size: typically ranges from 1 nm to 1000 nm.
Dispersion Medium
Definition
The continuous medium (solvent-like phase) in which colloidal particles are uniformly distributed.

Also called the external phase or continuous phase. It surrounds and supports the dispersed phase, forming the bulk of the system and influencing its physical properties.
Example
Water in milk. Air in smoke (aerosol). Water in jelly. Water in blood plasma.
note Can be solid, liquid, or gas — this determines the colloid type (sol, gel, aerosol, etc.).
🔎 Particle Size of a Colloid
🎨 Particle Representation of a Colloid
Colloidal Solution: Uniformly dispersed (Tyndall Effect)

Unlike suspension particles, colloidal particles remain uniformly distributed and do not settle down.

⚖️ Comparison Among Solution, Colloid and Suspension
Property Solution Colloid Suspension
Nature Homogeneous Apparently homogeneous Heterogeneous
Particle Size Less than 1 nm 1–1000 nm Greater than 1000 nm
Visibility Not visible Not visible individually Visible
Filtration Not separated Not separated by ordinary filtration Separated easily
Settling No settling No settling Settles down
📘 Definition
Tyndall Effect
🤔 Did You Know?
Why Does the Tyndall Effect Occur?
Colloidal particles are large enough to scatter incident light in different directions. When light strikes these particles, part of the light is reflected and scattered, making the path of the beam visible.
🎨 SVG Diagram
Visual Representation of Tyndall Effect
Tyndall Effect: Ocean Crepuscular Rays
✏️ Examples of Tyndall Effect in Daily Life
  • Sunlight entering a dusty room through a window.
  • Headlights visible in fog.
  • Projector beam visible in a cinema hall.
  • Sunrays passing through a dense forest.
  • Beam of light visible in smoke-filled air.
🏷️ Properties of a Colloid
Properties
Definition
A colloid is a heterogeneous mixture.
Visibility
Colloidal particles are too small to be seen individually by the naked eye.
Particle Size
The particle size ranges from 1 nm to 1000 nm.
Optical Property
Colloidal particles scatter light and exhibit the Tyndall effect.
Optical Effect
The path of a light beam becomes visible in a colloid.
Sedimentation
Colloidal particles do not settle down on standing.
Stability
Colloids are comparatively stable mixtures.
Filtration
They cannot be separated by ordinary filtration.
Separation
They can be separated using special techniques such as centrifugation.
✏️ Examples of Colloids
Colloid Dispersed Phase Dispersion Medium
Milk Fat Water
Fog Water droplets Air
Smoke Solid particles Air
Butter Water Fat
Blood Proteins and cells Plasma
Paint Pigment particles Liquid medium
⚡ Exam Tip
❌ Common Mistakes
  • Writing that colloids are homogeneous mixtures.
  • Confusing colloids with suspensions.
  • Assuming colloidal particles are visible to the naked eye.
  • Forgetting the particle size range of colloids.
  • Writing that colloids can be separated by filtration.
📋 CBSE Competency-Based Question

A student passes a beam of light through three samples: salt solution, milk, and muddy water.

In which sample will the Tyndall effect be observed most clearly?

Answer: Milk, because it is a colloid whose particles efficiently scatter light and make the light path visible.

🗒️ HOTS Question

Why does milk appear homogeneous even though it is actually a heterogeneous mixture?

Answer: The colloidal particles in milk are extremely small and uniformly distributed throughout the liquid. Therefore, individual particles cannot be distinguished by the naked eye, causing milk to appear homogeneous.

⚡ Quick Revision
  • Colloid = Heterogeneous mixture.
  • Particle size = 1–1000 nm.
  • Shows Tyndall effect.
  • Particles do not settle down.
  • Cannot be separated by ordinary filtration.
  • Can be separated by centrifugation.
  • Examples: Milk, blood, paint, fog, smoke.
⚗️

Dispersed Phase and Dispersion Medium

📋
Table of Contents
9 sections
🗺️ Overview
Every colloidal solution consists of two distinct components: the dispersed phase and the dispersion medium.
These two components together determine the nature and classification of a colloid. Understanding them is important for board examinations as well as higher studies in chemistry.
💡 Basic Concept
📘 Definition
Dispersed Phase
🔷 Characteristics of the Dispersed Phase
🔷 Characteristics
  • Present in smaller quantity.
  • Distributed throughout the dispersion medium.
  • Forms the discontinuous phase.
  • Responsible for scattering light in colloids.
📘 Definition
Dispersion Medium
🔷 Characteristics of the Dispersion Medium
🔷 Characteristics
  • Present in larger quantity.
  • Forms the continuous phase.
  • Provides the medium in which colloidal particles remain suspended.
  • Determines the physical state of the colloid.
🎨 Particle Representation
Dispersion Medium Continuous Fluid Phase Dispersed Phase Discontinuous Particles Colloid = Dispersed Phase + Dispersion Medium (Solute-like particles)     (Solvent-like fluid)
✏️ Example
Examples of Dispersed Phase and Dispersion Medium
Colloid Dispersed Phase Dispersion Medium
Milk Fat Globules Water
Fog Water Droplets Air
Smoke Solid Particles Air
Butter Water Fat
Paint Pigment Particles Liquid Medium
Blood Cells and Proteins Plasma
⚖️ Difference Between Dispersed Phase and Dispersion Medium
Dispersed Phase Dispersion Medium
The substance distributed as tiny particles throughout another substance. The substance in which the dispersed phase is distributed.
Present in smaller quantity. Present in larger quantity.
Forms the discontinuous phase. Forms the continuous phase.
Determines colloidal particle characteristics. Provides the suspension medium.
Example: Fat globules in milk. Example: Water in milk.
⚡ Exam Tip
⚗️

Centrifugation

📋
Table of Contents
9 sections
📘 Definition
🗒️ Principle Of Centrifugation
Centrifugation works on the principle that denser particles experience a greater outward force during rapid rotation and therefore separate from less dense particles.
This outward force is called centrifugal force.
🤔 Did You Know?
How Does Centrifugation Work?
  1. The mixture is placed in a centrifuge tube.
  2. The tube is rotated at high speed.
  3. Heavier particles move outward and settle at the bottom.
  4. Lighter liquid remains above.
  5. The separated layers can then be collected.
🎨 SVG Diagram
Working of a Centrifuge
RPM: 12,000 STATUS: SEPARATING... Centrifugation: Density-based Separation
🛠️ Applications of Centrifugation
  • Separating cream from milk.
  • Separating blood cells from plasma.
  • Purifying colloidal solutions.
  • Separating suspended impurities from liquids.
  • Medical and laboratory testing.
✏️ Example
Examples from Daily Life
  • Butter and cream separation from milk.
  • Spin-drying clothes in washing machines.
  • Laboratory blood tests.
  • Separation of impurities from edible oils.
⚖️ Comparison
Centrifugation vs Filtration
Centrifugation Filtration
Uses centrifugal force. Uses filter paper or porous medium.
Suitable for colloidal particles. Suitable for larger suspended particles.
Requires special equipment. Simple and inexpensive.
Very rapid separation. Comparatively slower.
📋 CBSE Competency-Based Question

A laboratory technician wants to separate blood cells from blood plasma. Which method should be used?

Answer: Centrifugation should be used because blood is a colloidal system and its components can be separated efficiently by high-speed spinning.

🗒️ HOTS Question

Why is centrifugation preferred over filtration for separating cream from milk?

Answer: The fat globules in milk are colloidal particles that are too small to be retained by ordinary filter paper. Centrifugation separates them based on density differences.

⚡ Quick Revision
  • Centrifugation uses centrifugal force.
  • Separates particles based on density.
  • Useful for colloids and fine suspensions.
  • Used in blood testing and cream separation.
  • Faster and more efficient than ordinary filtration for colloidal systems.
⚗️

Physical and Chemical Changes

📋
Table of Contents
18 sections
📘 Definition
📘 Definition

Physical Change

🔷 Characteristics of Physical Changes
🔷 Characteristics
  • No new substance is formed.
  • The chemical composition remains unchanged.
  • Usually reversible in nature.
  • Only physical properties change.
  • Very little energy is absorbed or released.
  • The original substance retains its identity.
✏️ Example
Examples of Physical Changes
  • Melting of ice.
  • Freezing of water.
  • Boiling of water.
  • Dissolving sugar in water.
  • Cutting paper into pieces.
  • Stretching a rubber band.
  • Breaking glass.
  • Sublimation of camphor.
🗒️ Particle Level Understanding

During a physical change, the particles of a substance rearrange themselves or change their motion, but their chemical identity remains unchanged.

For example, when ice melts:

\[ \text{H}_2\text{O (solid)} \rightarrow \text{H}_2\text{O (liquid)} \]

The substance remains water; only its physical state changes.

📘 Definition

Chemical Change

🗒️ Characteristics of Chemical Changes
  • One or more new substances are formed.
  • The chemical composition changes.
  • The original substance loses its identity.
  • Usually irreversible in nature.
  • Large amounts of energy may be absorbed or released.
  • New physical and chemical properties appear.
🗒️ Indicators Of A Chemical Change
  • Change in colour.
  • Evolution of gas.
  • Formation of a precipitate.
  • Change in temperature.
  • Production of light.
  • Development of smell.
✏️ Examples of Chemical Changes
  • Rusting of iron.
  • Burning of wood.
  • Burning of paper.
  • Digestion of food.
  • Curdling of milk.
  • Photosynthesis.
  • Respiration.
  • Cooking of food.
⚗️ Chemical Equation
Chemical Reaction Examples
Rusting of iron:
\[ \ce{\text{Iron}+\text{Oxygen}+\text{Water}\rightarrow\text{Rust}} \]
Burning of magnesium ribbon:
\[ \ce{2Mg + O_2 → 2MgO} \]
⚖️ Difference Between Physical Change and Chemical Change
Physical Change Chemical Change
No new substance is formed. New substance is formed.
Chemical composition remains unchanged. Chemical composition changes.
Generally reversible. Generally irreversible.
Original substance retains its identity. Original substance loses its identity.
Small energy changes. Large energy changes may occur.
No new properties appear. New properties appear.
Example: Melting of ice. Example: Rusting of iron.
🎨 SVG Diagram
Visual Representation
Physical Change Ice (Solid) → Water (Liquid) No New Substance Formed Chemical Change Iron + Oxygen → Iron Oxide New Substance Formed Comparison of Changes REVERSIBLE (Usually) IRREVERSIBLE (Usually)
🗒️ Importance in Daily Life
  • Cooking food involves chemical changes.
  • Water cycle mainly involves physical changes.
  • Rusting causes damage to bridges, vehicles, and machinery.
  • Photosynthesis is a chemical change that supports life on Earth.
  • Refrigeration works through physical changes of refrigerants.
✏️ Example
Solved Examples
Is dissolving sugar in water a physical or chemical change?
It is a physical change because no new substance is formed and sugar can be recovered by evaporation.
Why is rusting considered a chemical change?
Rusting produces a new substance called iron oxide (rust) having properties different from iron.
🗒️ CBSE Competency Based Question

A student performs the following activities:

  1. Melting ice.
  2. Burning paper.
  3. Dissolving salt in water.
  4. Rusting of iron.

Classify each change as physical or chemical.

Answer:

  • Melting ice → Physical Change
  • Burning paper → Chemical Change
  • Dissolving salt in water → Physical Change
  • Rusting of iron → Chemical Change
🗒️ HOTS Question

Why is melting of candle wax considered a physical change while burning of candle wax is a chemical change?

Answer:

During melting, only the state of wax changes and no new substance is formed. During burning, wax reacts with oxygen to form carbon dioxide, water vapour, and other substances, making it a chemical change.

❌ Common Mistakes
  • Assuming every irreversible change is chemical.
  • Classifying dissolution of salt as a chemical change.
  • Ignoring formation of new substances.
  • Confusing change of state with chemical change.
  • Writing that rusting is a physical change.
⚡ Exam Tip
⚡ Quick Revision
  • Physical Change → No new substance formed.
  • Chemical Change → New substance formed.
  • Physical Change → Usually reversible.
  • Chemical Change → Usually irreversible.
  • Melting of ice → Physical Change.
  • Rusting of iron → Chemical Change.
  • Burning of paper → Chemical Change.
  • Dissolving sugar in water → Physical Change.
⚗️

Elements

📋
Table of Contents
13 sections
📘 Definition
💡 Concept
Concept Builder
🗒️ Characteristics of Elements
  • Elements are pure substances.
  • Made up of only one type of atom.
  • Have fixed composition.
  • Cannot be broken down into simpler substances by ordinary chemical methods.
  • Possess definite physical and chemical properties.
  • Represented by unique chemical symbols.
  • May exist as atoms, molecules, or ions.
🤔 Did You Know?
Why Are Elements Important?
All compounds and mixtures are ultimately formed from elements.
For example:
  • Water is formed from hydrogen and oxygen.
  • Common salt is formed from sodium and chlorine.
  • Carbon forms the basis of organic compounds.
  • Oxygen is essential for respiration.
Thus, elements are the fundamental units of chemistry.
🗂️ Classification of Elements
Metals

Metals are elements that generally possess lustre, malleability, ductility, and good conductivity of heat and electricity.

General Properties of Metals
  • Shiny (lustrous) appearance.
  • Good conductors of heat and electricity.
  • Malleable (can be beaten into sheets).
  • Ductile (can be drawn into wires).
  • Usually hard and strong.
  • Generally solid at room temperature.
Examples
  • Iron (Fe)
  • Copper (Cu)
  • Gold (Au)
  • Silver (Ag)
  • Aluminium (Al)
Non-Metals

Non-metals are elements that generally do not possess metallic properties.

General Properties of Non-Metals
  • Poor conductors of heat and electricity.
  • Usually brittle in solid state.
  • Not malleable or ductile.
  • May exist as solids, liquids, or gases.
  • Generally have dull appearance.
Examples
  • Oxygen (O)
  • Nitrogen (N)
  • Hydrogen (H)
  • Carbon (C)
  • Sulphur (S)
Metalloids

Metalloids are elements that exhibit properties intermediate between metals and non-metals.

They possess characteristics of both groups.

Examples
  • Boron (B)
  • Silicon (Si)
  • Germanium (Ge)
  • Arsenic (As)
  • Antimony (Sb)
⚖️ Comparison of Metals, Non-Metals and Metalloids
Property Metals Non-Metals Metalloids
Appearance Lustrous Dull Intermediate
Conductivity Good Poor Moderate
Malleability Present Absent Limited
Ductility Present Absent Limited
Examples Fe, Cu, Au O, N, S Si, B, Ge
🗒️ Chemical Symbols Of Common Elements
Element Symbol
Hydrogen H
Oxygen O
Nitrogen N
Carbon C
Sulphur S
Iron Fe
Copper Cu
Silver Ag
Gold Au
Sodium Na
⚖️ Difference Between Elements and Compounds
Element Compound
Contains one type of atom. Contains two or more different elements chemically combined.
Cannot be broken into simpler substances. Can be decomposed chemically.
Represented by symbols. Represented by formulae.
Examples: Fe, O, Au Examples: H₂O, CO₂, NaCl
📋 CBSE Competency-Based Question

A student is given four substances: Oxygen, Water, Copper, and Carbon Dioxide.

Identify which are elements.

Answer:

  • Oxygen → Element
  • Copper → Element
  • Water → Compound
  • Carbon Dioxide → Compound
🗒️ HOTS Question

Diamond and graphite have completely different physical properties, yet both are considered the same element. Why?

Answer:

Both diamond and graphite are made entirely of carbon atoms. Since they contain only one type of atom, both are forms (allotropes) of the same element, carbon.

❌ Common Mistakes
  • Confusing elements with compounds.
  • Assuming all elements exist as single atoms.
  • Writing water as an element.
  • Thinking elements can be separated physically.
  • Ignoring the difference between symbols and formulae.
⚡ Exam Tip
⚡ Quick Revision
  • Element = Pure substance.
  • Contains only one type of atom.
  • Cannot be broken down chemically.
  • Classified into metals, non-metals, and metalloids.
  • Represented by chemical symbols.
  • Examples: Oxygen, Iron, Gold, Carbon.
🎨 SVG Diagram
Classification of Matter
Matter (Solid, Liquid or Gas) Pure Substance Mixtures (No Fixed Comp.) Elements Cannot be broken down into simpler substances Examples: Copper, Oxygen, Iron, Hydrogen, Mercury, etc. Compounds Fixed composition. Can be broken down by chemical or electrochemical reactions. Examples: Water, Methane, Sugar, Salt, etc. Homogeneous Uniform composition Examples: Sugar in water, Salt in water, Water in alcohol, etc. Heterogeneous Non-uniform composition Examples: Sand and salt, Sugar and salt, Water in oil, etc. Matter Classification Overview
· Updated
⚗️

Ductility

📋
Table of Contents
8 sections
📘 Definition
💡 Concept Builder
🤔 Did You Know?
Why Are Metals Ductile?
Metals consist of layers of atoms arranged in a regular pattern. These layers can slide over one another when force is applied without causing the metal to break.
Because of this atomic arrangement, metals can be stretched into wires while maintaining their structure.
🔷 Characteristics of Ductility
🔷 Characteristics
  • It is a physical property of matter.
  • It is mainly observed in metals.
  • Highly ductile materials can be converted into thin wires.
  • No new substance is formed during the process.
  • Ductility helps materials withstand tensile stress.
  • Ductile materials deform before breaking.
✏️ Examples of Ductile Materials
Material Use Due to Ductility
Copper Electrical wires
Aluminium Transmission cables
Gold Fine jewellery wires
Silver Electrical conductors
Platinum Laboratory equipment
📌 Note
Most Ductile Metal
🛠️ Applications of Ductility
  • Manufacture of electrical wires.
  • Production of communication cables.
  • Construction of transmission lines.
  • Jewellery manufacturing.
  • Industrial wire production.
  • Electronic circuit fabrication.
⚡ Quick Revision
  • Ductility is the ability to be drawn into wires.
  • It is a physical property of metals.
  • Gold is the most ductile metal.
  • Copper and aluminium are highly ductile.
  • Ductility is important in electrical wiring.
  • Do not confuse ductility with malleability.
⚗️

Malleability

📋
Table of Contents
10 sections
📘 Definition
💡 Concept Builder
🤔 Did You Know?
Why Are Metals Malleable?
Metals consist of closely packed layers of atoms. When pressure is applied, these layers slide over one another without breaking the metallic bond.
As a result, the metal changes shape instead of fracturing.
This atomic arrangement makes most metals highly malleable.
🔷 Characteristics of Malleability
🔷 Characteristics
  • It is a physical property of matter.
  • Commonly observed in metals.
  • Allows conversion of metals into thin sheets.
  • No new substance is formed during the process.
  • Associated with compressive force.
  • Important for industrial shaping and manufacturing.
✏️ Examples of Malleable Metals
Metal Common Use
Gold Gold leaf, jewellery
Silver Decorative sheets, ornaments
Aluminium Foils and packaging
Copper Industrial sheets and roofing
Lead Protective sheets and batteries
📌 Note
Most Malleable Metal
⚖️ Difference Between Malleability and Ductility
Malleability Ductility
Ability to form sheets. Ability to form wires.
Associated with compressive force. Associated with tensile force.
Metal is hammered or rolled. Metal is stretched or drawn.
Example: Aluminium foil. Example: Copper wire.
Most malleable metal: Gold. Most ductile metal: Gold.
🌟 Importance of Malleability
✏️ Example
Examples from Daily Life
  • Aluminium foil used in kitchens.
  • Gold leaf used in decorations and sweets.
  • Metal sheets used in vehicles.
  • Steel sheets used in construction.
  • Copper sheets used in roofing.
⚡ Quick Revision
  • Malleability is the ability to be hammered into sheets.
  • It is a physical property.
  • Observed mainly in metals.
  • Gold is the most malleable metal.
  • Used in making foils, sheets, and jewellery.
  • Do not confuse malleability with ductility.
⚗️

Sonorous

📋
Table of Contents
4 sections
📘 Definition
💡 Concept Builder
🤔 Did You Know?
Why Are Metals Sonorous?
Metals possess closely packed particles connected by strong metallic bonds.
When struck, these particles vibrate rapidly and transfer vibrations efficiently throughout the material.
These vibrations produce sound waves that travel through the air and reach our ears as a ringing sound.
✏️ Examples of Sonorous Materials
Material Common Application
Brass Bells and musical instruments
Bronze Temple bells and gongs
Steel Musical instruments and tools
Iron Industrial signaling devices
Aluminium Musical components
⚗️

Non-Metals

📋
Table of Contents
13 sections
📘 Definition
💡 Concept Builder
🗒️ Occurrence Of Non Metals
Non-metals are found in all three physical states.
Physical State Examples
Solid Carbon, Sulphur, Phosphorus, Iodine
Liquid Bromine
Gas Oxygen, Nitrogen, Hydrogen, Chlorine
🏷️ Properties of Non-Metals
Properties
Appearance
They display a variety of colours.
Electrical Conductivity
They are poor conductors of heat and electricity.
Lustre
They are generally not lustrous.
Sound
They are not sonorous.
Malleability
They are not malleable.
Ductility
They are not ductile.
Hardness
Most non-metals are brittle in solid form.
Density
They generally have lower densities than metals.
Physical State
Many non-metals exist as gases at room temperature.
🌟 Important Examples of Non-Metals
🗒️ Important Exceptions To Remember
Exception Explanation
Graphite A non-metal that conducts electricity.
Diamond Hardest naturally occurring substance.
Iodine A lustrous non-metal.
Bromine Only liquid non-metal at room temperature.
⚖️ Difference Between Metals and Non-Metals
Metals Non-Metals
Good conductors of heat and electricity. Poor conductors of heat and electricity.
Lustrous. Generally non-lustrous.
Malleable. Non-malleable.
Ductile. Non-ductile.
Sonorous. Non-sonorous.
Usually solids. Can be solids, liquids, or gases.
🌟 Importance of Non-Metals in Daily Life
✏️ Example
Solved Examples
Why are non-metals generally poor conductors of electricity?
Non-metals generally lack free electrons that can carry electric current.
Name the only liquid non-metal.
Bromine.
Which non-metal conducts electricity?
Graphite
🗒️ HOTS Question

Graphite is a non-metal, yet it is used in electrodes. Why?

Answer:

Graphite contains free electrons that can move through its structure, making it a good conductor of electricity. Therefore, it is used in electrodes.

❌ Common Mistakes
  • Writing that all non-metals are gases.
  • Forgetting that bromine is a liquid non-metal.
  • Ignoring graphite as an electrical conductor.
  • Assuming all non-metals are dull.
  • Confusing iodine with a metal because of its lustre.
⚡ Exam Tip
⚡ Quick Revision
  • Non-metals are poor conductors of heat and electricity.
  • Generally non-lustrous, non-sonorous, non-malleable, and non-ductile.
  • Exist as solids, liquids, and gases.
  • Bromine is the only liquid non-metal.
  • Graphite conducts electricity.
  • Diamond is the hardest natural substance.
  • Examples: Oxygen, Nitrogen, Carbon, Sulphur, Phosphorus.
⚗️

Metalloids

📋
Table of Contents
12 sections
📘 Definition
💡 Concept Builder
🗒️ Position Of Metalloids In The Periodic Table

Metalloids are located between metals and non-metals in the periodic table.

They lie along the staircase-shaped boundary that separates metallic elements from non-metallic elements.

🎨 SVG Diagram
Mettaloids in Periodic Table
METALLOIDS IN THE PERIODIC TABLE B Si Ge As Sb Te Po At Metalloids Metals Non-Metals
🏷️ Properties
Properties of Metalloids
Properties
Chemical Nature
Demonstrate a hybrid of metallic and non-metallic chemical behaviors.
Physical State
Typically exist as solids under standard temperature and pressure conditions.
Mechanical Behavior
Characteristically brittle, lacking the malleability and ductility found in true metals.
Appearance
Frequently exhibit a distinct metallic lustre or shiny surface finish.
Conductivity
Possess intermediate electrical conductivity—superior to insulators but inferior to conductors.
Electronic Property
Function as effective semiconductors, with conductivity often increasing as temperature rises.
Industrial Use
Integral to the fabrication of microchips, transistors, and high-performance electronics.
🔎 Semiconductor Nature of Metalloids
⚖️ Common Metalloids
Metalloid Symbol Important Use
Boron B Glass and ceramics
Silicon Si Computer chips and solar cells
Germanium Ge Semiconductors and transistors
Arsenic As Electronic components
Antimony Sb Alloys and batteries
Tellurium Te Solar technology
🤔 Did You Know?
Why Is Silicon Important?

Silicon is the most commercially important metalloid.

Due to its semiconductor properties, it is used in:

  • Computer processors.
  • Integrated circuits (ICs).
  • Mobile phones.
  • Laptops and tablets.
  • Solar panels.
  • Microchips.

For this reason, silicon is often called the "backbone of modern electronics."

⚖️ Comparison of Metals, Metalloids and Non-Metals
Property Metals Metalloids Non-Metals
Appearance Lustrous Usually lustrous Generally dull
Conductivity High Intermediate Low
Malleability Malleable Brittle Non-malleable
Ductility Ductile Generally non-ductile Non-ductile
Electrical Nature Conductors Semiconductors Insulators
Examples Iron, Copper Silicon, Boron Oxygen, Sulphur
🛠️ Applications of Metalloids
  • Manufacturing computer chips.
  • Production of transistors.
  • Fabrication of integrated circuits.
  • Solar cell manufacturing.
  • Electronic communication systems.
  • Glass and ceramic industries.
✏️ Example
Solved Example
Why is silicon classified as a metalloid?
Silicon exhibits both metallic and non-metallic properties and behaves as a semiconductor. Therefore, it is classified as a metalloid.
Name two commonly used metalloids.
Silicon and germanium.
⚡ Exam Tip
⚡ Quick Revision
  • Metalloids possess both metallic and non-metallic properties.
  • Examples: Silicon, Boron, Germanium, Arsenic, Antimony.
  • Most metalloids are semiconductors.
  • Used in electronics and computer industries.
  • Located between metals and non-metals in the periodic table.
  • Silicon is the most important metalloid.
⚗️

Compound

📋
Table of Contents
11 sections
📘 Definition
💡 Concept Builder
🔷 Characteristics of Compounds
🔷 Characteristics
  • Compounds are pure substances.
  • Formed by chemical combination of elements.
  • Elements combine in a fixed proportion by mass.
  • Properties differ from constituent elements.
  • Represented by chemical formulae.
  • Cannot be separated by physical methods.
  • Can be decomposed only by chemical reactions.
  • Have definite melting and boiling points.
🤔 Did You Know?
How Are Compounds Formed?
Compounds are formed when atoms of different elements react chemically and establish chemical bonds.

During compound formation:
  1. Atoms of different elements combine.
  2. Chemical bonds are formed.
  3. Energy may be released or absorbed.
  4. A completely new substance is produced.
✏️ Common Examples of Compounds
Compound Chemical Formula Constituent Elements
Water H₂O Hydrogen + Oxygen
Carbon Dioxide CO₂ Carbon + Oxygen
Common Salt NaCl Sodium + Chlorine
Ammonia NH₃ Nitrogen + Hydrogen
Methane CH₄ Carbon + Hydrogen
Calcium Carbonate CaCO₃ Calcium + Carbon + Oxygen
✏️ Example
Solved Example
Why is water considered a compound?
Water consists of hydrogen and oxygen chemically combined in a fixed ratio. Therefore, it is a compound.
Can the components of a compound be separated by filtration?
No. Compounds can be separated only by chemical methods.
📋 CBSE Competency-Based Question

A student compares water and a mixture of hydrogen and oxygen gases.

Which one is a compound and why?

Answer: Water is a compound because hydrogen and oxygen are chemically combined in a fixed ratio. The mixture of hydrogen and oxygen gases is only a physical mixture.

🗒️ HOTS Question

Hydrogen is combustible and oxygen supports combustion. Why does water not show either of these properties?

Answer:

When elements combine chemically, a new substance with entirely different properties is formed. Therefore, water possesses properties different from both hydrogen and oxygen.

❌ Common Mistakes
  • Confusing compounds with mixtures.
  • Writing that compounds have variable composition.
  • Assuming compounds can be separated physically.
  • Ignoring fixed proportions in compounds.
  • Confusing symbols with formulae.
⚡ Exam Tip
⚡ Quick Revision
  • Compound = Pure substance.
  • Formed by chemical combination of elements.
  • Fixed composition.
  • Properties differ from constituent elements.
  • Represented by chemical formulae.
  • Separated only by chemical methods.
  • Examples: Water, Carbon Dioxide, Common Salt.
⚗️

Important Points to Remember

📋
Table of Contents
3 sections
🗒️ Importance
The following points summarize the complete chapter and are highly useful for CBSE examinations, competency-based questions, assertion-reason questions, multiple-choice questions (MCQs), and last-minute revision.
  • Matter is anything that has mass and occupies space.
  • Matter can broadly be classified into pure substances and mixtures.
  • A pure substance contains only one type of particle and has a fixed composition throughout.
  • Pure substances are classified into elements and compounds.
  • An element consists of only one type of atom and cannot be broken down into simpler substances by ordinary chemical methods.
  • Compounds are formed when two or more elements combine chemically in a fixed ratio.
  • The properties of a compound are entirely different from those of its constituent elements.
  • A mixture contains two or more substances physically mixed in any proportion.
  • The components of a mixture retain their individual properties.
  • Mixtures can be separated by suitable physical methods such as filtration, evaporation, distillation, centrifugation, sublimation, magnetic separation, chromatography, and crystallization.
  • Mixtures may be homogeneous or heterogeneous.
  • Homogeneous mixtures have uniform composition throughout the mixture.
  • Heterogeneous mixtures have non-uniform composition and visibly distinct phases.
  • A solution is a homogeneous mixture of two or more substances.
  • The component present in larger quantity is called the solvent.
  • The component present in smaller quantity is called the solute.
  • Solution particles are generally smaller than \[ 1 \text{ nm} \] in size.
  • Solution particles do not scatter light and therefore do not show the Tyndall effect.
  • Solute particles cannot be separated from a true solution by ordinary filtration.
  • The concentration of a solution expresses the amount of solute present in a given amount of solvent or solution.
  • Mass percentage of a solution is calculated using:

\[ \text{Mass Percentage} = \frac{\text{Mass of Solute}} {\text{Mass of Solution}} \times 100 \]

  • A saturated solution contains the maximum amount of solute that can dissolve at a given temperature.
  • An unsaturated solution can still dissolve more solute at the same temperature.
  • A suspension is a heterogeneous mixture containing visible particles.
  • Suspension particles settle down on standing.
  • Suspensions can be separated by filtration.
  • Colloids are heterogeneous mixtures that appear homogeneous.
  • Colloidal particle size generally lies between:

\[ 1 \text{ nm} \; \text{to} \; 1000 \text{ nm} \]

  • Colloidal particles do not settle down under ordinary conditions.
  • Colloids scatter light and show the Tyndall effect.
  • Milk, fog, smoke, blood, and paint are common examples of colloids.
  • In a colloid, the particles distributed throughout the medium are called the dispersed phase.
  • The medium in which the particles are distributed is called the dispersion medium.
  • Centrifugation separates components based on differences in density using centrifugal force.
  • Physical changes do not produce new substances.
  • Chemical changes result in the formation of new substances with different properties.
  • Metals are generally lustrous, malleable, ductile, sonorous, and good conductors of heat and electricity.
  • Non-metals are generally dull, brittle, non-sonorous, and poor conductors of heat and electricity.
  • Metalloids show properties of both metals and non-metals.
  • Silicon is the most important metalloid because of its semiconductor properties.
🔎 Key Fact
Most Important Examination Facts
📝 Chapter Conclusion
· Updated
NCERT Science · Class IX · Chapter 2

Is Matter Around Us Pure?

A complete interactive learning engine — concepts, formulas, AI-powered step-by-step solver, tricks & tips, common mistakes, and rich practice questions with full solutions.

9 Concept Groups 30 Practice Questions AI Step-by-Step Solver Flash Cards · Match Game · MCQ Quiz

Core Concept Groups

01

Pure Substances vs Mixtures

Matter is classified into pure substances (fixed composition) and mixtures (variable composition). Pure substances have definite melting/boiling points; mixtures do not. A pure substance is either an element or a compound.

ClassificationComposition
02

Elements & Compounds

An element cannot be broken into simpler substances chemically (e.g., Fe, O₂, Na). A compound is formed by chemical combination of two or more elements in a fixed mass ratio (e.g., H₂O, NaCl, CO₂). Compounds have properties entirely different from constituent elements.

ElementsCompoundsChemical Bonding
03

Types of Mixtures

Homogeneous mixtures (solutions) have a uniform composition throughout — the solute is uniformly distributed. Heterogeneous mixtures have non-uniform composition — components can be distinguished visually (e.g., soil, blood, fog).

HomogeneousHeterogeneousSolution
04

Solutions — Solute, Solvent, Concentration

A solution = solute + solvent. Solute is the dissolved substance; solvent is the medium. Concentration can be expressed as mass percent = (mass of solute / mass of solution) × 100. A saturated solution holds maximum solute at a given temperature.

SoluteSolventConcentrationSaturation
05

Suspensions

A suspension is a heterogeneous mixture where solute particles are larger than 1000 nm. They settle on standing, are visible to the naked eye, and scatter a beam of light (Tyndall Effect is visible). Particles can be filtered through ordinary filter paper.

Particle Size >1000 nmSettlesFilterable
06

Colloids (Colloidal Solutions)

Colloid particles range from 1 nm to 1000 nm. They do not settle, cannot be filtered with ordinary filter paper, and show the Tyndall Effect. Examples: milk (emulsion), smoke (aerosol), foam, sols, gels. The dispersed phase is particles; dispersion medium is the medium.

1–1000 nmTyndall Effect8 Types
07

Separation Techniques

Methods vary by property exploited: Evaporation (volatile solvent), Centrifugation (density, for colloids/blood), Distillation (different boiling points), Chromatography (different solubility in mobile phase), Sublimation (camphor, iodine), Magnetic separation, Crystallisation (purity), Fractional distillation (miscible liquids, <25°C bp difference).

EvaporationDistillationChromatographyCrystallisation
08

Physical & Chemical Changes

A physical change is reversible, no new substance is formed, and chemical composition unchanged (melting, dissolving). A chemical change is usually irreversible, new substances form with different properties — accompanied by heat, light, gas, precipitate, or colour change.

ReversibleIrreversibleNew Substance
09

Tyndall Effect & Brownian Motion

The Tyndall Effect is the scattering of a beam of light by colloidal particles — it distinguishes colloids from true solutions (solutions do not show it). Brownian Motion is the random zig-zag movement of colloidal particles due to unequal bombardment by the dispersion medium molecules — this keeps them from settling.

Light ScatteringColloid IDStability

Comparison: Solution vs Colloid vs Suspension

Property True Solution Colloid Suspension
Particle Size< 1 nm1 – 1000 nm> 1000 nm
VisibilityNot visibleNot visible (microscope needed)Visible to naked eye
Tyndall EffectAbsentPresentPresent
SettlingDoes not settleDoes not settleSettles on standing
FiltrationPasses filter paperPasses filter paperRetained by filter paper
StabilityVery stableModerately stableUnstable
ExamplesSalt water, sugar waterMilk, smoke, bloodSand in water, chalk water

8 Types of Colloidal Systems

Type Dispersed Phase Dispersion Medium Example
FoamGasLiquidShaving cream, whipped cream
Solid FoamGasSolidPumice stone, bread
EmulsionLiquidLiquidMilk, mayonnaise
GelLiquidSolidJelly, cheese
SolSolidLiquidPaint, muddy water
Solid SolSolidSolidColoured gemstones, alloys
Aerosol (liquid)LiquidGasFog, cloud, mist
Aerosol (solid)SolidGasSmoke, dust in air

Key Formulas & Expressions

Mass Percentage (w/w)
w/w% = (m_solute / m_solution) × 100
Expresses concentration as mass of solute per 100 g of solution. Most common in NCERT problems.
m_solute = mass of dissolved substance (g) m_solution = m_solute + m_solvent
Volume Percentage (v/v)
v/v% = (V_solute / V_solution) × 100
Used when both solute and solvent are liquids (e.g., alcohol in water). V in mL or L.
V_solute = volume of solute (mL) V_solution = total volume of solution
Mass-Volume Percentage (w/v)
w/v% = (m_solute / V_solution) × 100
Mass of solute (g) per 100 mL of solution. Commonly used in medical/pharmaceutical contexts.
m_solute in grams V_solution in mL
Amount of Solute (from w/w%)
m_solute = (w/w% × m_solution) / 100
Rearranged form to find actual mass of solute when concentration and solution mass are known.
Result in grams
Density Relationship
ρ = m / V
Density of solution links mass and volume. Used to convert between w/w% and w/v% when density is given.
ρ = density (g/mL or g/cm³) m = mass (g) V = volume (mL or cm³)
Conversion: w/w% → w/v%
w/v% = w/w% × ρ
If density (ρ, g/mL) of solution is known, multiply w/w% by density to get w/v% concentration.
ρ in g/mL Valid for dilute aqueous solutions
Boiling Point Elevation (Concept)
ΔT_b = K_b × m (intro concept)
A colligative property: dissolving solute in solvent raises its boiling point. Salt water boils above 100°C. (Formula reference for enrichment.)
K_b = boiling point constant m = molality
Particle Size Ranges
Solution: d < 1 nm
Colloid: 1 nm ≤ d ≤ 1000 nm
Suspension: d > 1000 nm
Key discriminating criterion for classifying mixtures in NCERT Science IX.

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Fully Worked Examples

Example 1 w/w%

Problem: 20 g of NaCl is dissolved in 80 g of water. Calculate the mass percentage of the solution.

1
Identify given values:
Mass of solute (NaCl) = 20 g, Mass of solvent (water) = 80 g
2
Find mass of solution:
m_solution = 20 + 80 = 100 g
3
Apply formula:
w/w% = (20 / 100) × 100 = 20%
4
State answer:
The mass percentage of NaCl = 20% (w/w)
Example 2 w/v%

Problem: 5 g of glucose is dissolved in enough water to make 100 mL of solution. Find w/v%.

1
Given: m_solute = 5 g, V_solution = 100 mL
2
Formula: w/v% = (m_solute / V_solution) × 100
3
Calculate: w/v% = (5 / 100) × 100 = 5%
4
Answer: Glucose solution = 5% w/v
Example 3 Separation

Problem: How would you separate a mixture of acetone (b.p. 56°C) and water (b.p. 100°C)? Justify.

1
Identify type: Acetone and water are miscible liquids with different boiling points.
2
Check bp difference: 100 – 56 = 44°C > 25°C, so simple distillation works.
3
Process: Heat to 56°C. Acetone vaporises first, condenses in condenser, collected separately. Water remains.
4
Method: Simple Distillation. If bp difference were <25°C, fractional distillation would be used.

Tricks & Tips

💡

The "mass of solution" trick Always remember: m_solution = m_solute + m_solvent. Students often use m_solvent in the denominator — it's always the solution!

🎯

Tyndall = Colloid ID Card If light scatters in a mixture, it's a colloid. True solutions are transparent to a beam of light.

🔢

Particle size mnemonics Remember: "1 and 1000" — colloids live between 1 nm and 1000 nm. Below = solution, Above = suspension.

🧲

Choosing separation Ask: Are they miscible? → distillation. Are they magnetic? → magnetic separation. Is one volatile? → evaporation/sublimation.

🔬

Compound vs Mixture Fixed ratio + energy change during formation + can only be separated chemically = compound. Otherwise = mixture.

📊

Chromatography direction Solute that is MORE soluble in mobile phase travels farther up the paper. Polarity matters.

🌡️

Fractional vs Simple Distillation If boiling point difference <25°C → fractional distillation (fractionating column needed). >25°C → simple distillation suffices.

⚗️

Crystallisation over evaporation Use crystallisation when solute decomposes on heating OR when you need a purer product. Evaporation is simpler but less pure.

Common Mistakes

❌

Confusing solvent with solution w/w% = (m_solute / m_solution) × 100, NOT m_solvent in denominator.

❌

Mixing up colloid and suspension examples Milk is a colloid (emulsion), NOT a suspension. Muddy water is a suspension, NOT a colloid.

❌

Saying blood is a solution Blood is a colloid — it shows the Tyndall Effect and its particles don't settle readily.

❌

Calling dissolution a chemical change Dissolving sugar in water is a physical change — no new substance forms and it's reversible.

❌

Brownian motion = Tyndall Effect These are different phenomena. Tyndall = light scattering; Brownian = random particle movement.

❌

Assuming all alloys are solutions Alloys ARE solutions (solid solutions), but students often call them mixtures or compounds — they are homogeneous mixtures.

❌

Confusing chromatography with distillation Chromatography separates based on differential solubility/adsorption, NOT boiling point.

❌

Ignoring units in w/v% w/v% requires mass in grams and volume in mL. Mixing units (g and L) is a very common error.

Solutions & Concentration

Application
A pharmacist prepares a saline drip by dissolving 9 g of NaCl in enough water to make 1000 mL of solution. Calculate the w/v% concentration. Is this solution hypertonic, hypotonic, or isotonic with respect to blood?
Full Solution
1
Given: m_solute = 9 g, V_solution = 1000 mL
2
Formula: w/v% = (m_solute / V_solution) × 100
3
Calculate: w/v% = (9 / 1000) × 100 = 0.9% w/v
4
Compare with blood: Normal saline is exactly 0.9% NaCl — this is isotonic with blood plasma, meaning it won't cause cells to shrink or burst. This is why it is used in IV drips.
Application
250 g of sugar solution contains 40 g of sugar. Find: (a) mass% of sugar, (b) mass of solvent present.
Full Solution
1
Given: m_solution = 250 g, m_solute (sugar) = 40 g
2
(a) Mass%: = (40 / 250) × 100 = 16%
3
(b) Mass of solvent: m_solvent = m_solution – m_solute = 250 – 40 = 210 g of water
Analytical
A solution has density 1.2 g/mL and w/w% of HCl = 36%. Calculate the w/v% concentration of this solution.
Full Solution
1
Given: ρ = 1.2 g/mL, w/w% = 36%
2
Relationship: w/v% = w/w% × density = 36 × 1.2 = 43.2% w/v
3
Verify by logic: 100 g of solution → 36 g HCl. Volume of 100 g solution = 100/1.2 = 83.3 mL. w/v% = (36/83.3)×100 = 43.2% ✓

Colloids, Solutions & Suspensions

Conceptual
Why does a beam of light passing through a colloid become visible, but the same beam passing through a true solution remains invisible?
Full Solution
1
Key principle: Light is scattered (deflected) when it strikes particles comparable in size to its wavelength.
2
In a colloid: Particles are 1–1000 nm — large enough to scatter visible light. The scattered light makes the path visible → Tyndall Effect.
3
In a true solution: Solute particles are <1 nm (ion/molecule-sized) — too small to scatter visible light. Light passes straight through; path is invisible.
4
Conclusion: Tyndall Effect is a reliable diagnostic tool — its presence confirms a colloidal system; its absence indicates a true solution.
Analytical
A student adds camphor to common salt (NaCl) and heats the mixture gently. Describe and explain each observation at every stage, and name the separation technique used.
Full Solution
1
Technique: Sublimation — camphor converts directly from solid → gas (sublimes), skipping the liquid phase. NaCl does not sublime.
2
Stage 1 (gentle heating): Camphor begins to sublime, forming white vapour above the mixture. NaCl remains unchanged as solid.
3
Stage 2 (cooling): Camphor vapour re-solidifies (deposits) on cooler parts of the vessel (inverted funnel). NaCl collects at the bottom.
4
Result: Pure camphor crystals on funnel; pure NaCl remains in dish. Clean, efficient separation with no solvents needed.
HOTS
Why does fog persist for long periods and does not settle, even though its droplets are heavier than air molecules? Connect this to the stability of colloidal systems.
Full Solution
1
Fog is a colloid: It is an aerosol — liquid droplets (dispersed phase) dispersed in gas/air (dispersion medium). Droplet size: 1–1000 nm range.
2
Brownian Motion: Fog droplets undergo continuous, random Brownian motion — air molecules bombard them from all sides unequally, keeping them in suspension and preventing settling.
3
Surface charge: Colloidal particles carry like electric charges on their surfaces. These charges repel each other, preventing aggregation and settling.
4
Conclusion: Brownian motion + surface charge = kinetic and electrostatic stability. This is why colloids don't settle despite gravity.

Separation Techniques

Analytical
A mixture contains iron filings, sand, ammonium chloride, and common salt. Outline the steps to separate all four components completely, in the correct order.
Full Solution
1
Step A — Magnetic Separation: Pass a magnet over the mixture. Iron filings are attracted and removed. Remaining mixture: sand + NH₄Cl + NaCl.
2
Step B — Sublimation: Gently heat the remaining mixture. Ammonium chloride (NH₄Cl) sublimes and deposits on a cool funnel. Sand + NaCl remain.
3
Step C — Dissolving + Filtration: Add water. NaCl dissolves; sand does not. Filter. Sand is retained in filter paper.
4
Step D — Evaporation/Crystallisation: Evaporate the filtrate (NaCl solution) or allow slow crystallisation. NaCl crystals obtained.
Conceptual
In paper chromatography of a leaf extract, two pigments A and B are separated. A travels 8 cm and B travels 5 cm in the same time. Which pigment is more soluble in the mobile phase and why?
Full Solution
1
Principle: In paper chromatography, components travel up the paper carried by the mobile phase (solvent). More soluble = travels further = higher Rf value.
2
Rf of A: Rf_A = 8 / (distance of solvent front) → relatively higher
3
Rf of B: Rf_B = 5 / same distance → lower than A
4
Conclusion: Pigment A is more soluble in the mobile phase because it is carried further up the chromatography paper.

Elements, Compounds & Physical/Chemical Changes

HOTS
Steel (Fe + C) and water (H₂O) both involve iron/hydrogen and carbon/oxygen. One is a mixture, one is a compound. Using three criteria, distinguish between steel and water, and justify your classification.
Full Solution
1
Composition ratio: Water always has H:O = 2:1 by atoms (fixed). Steel's carbon content varies (0.2–2.1%) — no fixed ratio. → Steel = mixture; Water = compound.
2
Properties vs components: Water's properties differ completely from H₂ and O₂. Steel's properties (hardness, malleability) are intermediate/modified versions of iron. → Water = compound; Steel = mixture.
3
Separation method: Steel can be separated by physical means (dissolving in acid, or phase separation at correct temperature). Water can only be separated into H₂ and O₂ by electrolysis (chemical method). → Steel = mixture; Water = compound.
4
Conclusion: Steel = heterogeneous mixture (alloy). Water = compound. Both criteria reinforce each other.
Conceptual
Is dissolving copper sulphate in water a physical or chemical change? What happens if you evaporate all the water? Use this to support your answer.
Full Solution
1
Observation on dissolving: CuSO₄ disperses in water, forming a blue solution. No new substance forms — CuSO₄ ions separate but recombine on reversal.
2
Reversibility test: On evaporation, blue CuSO₄ crystals are recovered intact — same chemical identity, same formula, same properties.
3
Classification: Since the original substance can be recovered unchanged by a physical process (evaporation) = Physical Change.
4
Note: Heating CuSO₄·5H₂O to high temperature (dehydration) IS a chemical change — a new anhydrous form is produced. Dissolving at room temperature is NOT.
HOTS
Air near a busy road contains dust, CO₂, N₂, SO₂, and water vapour. Classify this as a mixture/compound, identify its type (homogeneous/heterogeneous), and suggest one technique to detect if a specific gas like CO₂ is present.
Full Solution
1
Classification: Air is a mixture — its composition varies (more CO₂ near roads), it can be separated by physical means (fractional distillation of liquid air), and no energy change occurs in formation.
2
Type: Normally air is homogeneous, but near a busy road with dust particles, it becomes heterogeneous (dust = suspension in air = aerosol).
3
CO₂ detection: Bubble the air sample through lime water (Ca(OH)₂ solution). CO₂ reacts to form white milky precipitate of CaCO₃ — a chemical test. Alternatively, use a CO₂ sensor for quantitative analysis.
4
Dust removal: Use an electrostatic precipitator or filter to remove suspended dust particles — appropriate because dust forms an aerosol (colloidal system).
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Is Matter Around Us Pure | Science Class 9 | Academia Aeternum
Is Matter Around Us Pure | Science Class 9 | Academia Aeternum — Complete Notes & Solutions · academia-aeternum.com
The world around us is made up of different kinds of substances, but are all of them pure? In this chapter, Is Matter Around Us Pure, we explore the difference between pure substances and mixtures, and learn how to identify them. You will study homogeneous and heterogeneous mixtures, solutions, colloids, and suspensions, along with interesting phenomena like the Tyndall effect. The chapter also introduces important separation techniques such as filtration, evaporation, crystallization,…
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    Frequently Asked Questions

    A pure substance consists of only one kind of particles with a fixed composition throughout.

    Impurities are unwanted substances mixed with a pure substance that alter its composition and properties.

    Elements and compounds are the two categories of pure substances.

    An element is a substance made up of only one type of atom, for example, hydrogen or oxygen.

    A compound is a pure substance formed by the chemical combination of two or more elements in fixed proportions.

    Water (H2O) is a compound made from hydrogen and oxygen.

    A mixture is a combination of two or more substances physically mixed but not chemically combined.

    Mixtures are of two types: homogeneous and heterogeneous.

    A homogeneous mixture has uniform composition and appearance throughout, like salt dissolved in water.

    A heterogeneous mixture has visibly different components and non-uniform distribution, like sand in water.

    Evaporation method is used to obtain common salt from sea water.

    Air is a homogeneous mixture of various gases like nitrogen, oxygen, and carbon dioxide.

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