Chapter – 2

Is Matter Around Us Pure

In this post we have given the detailed notes of class 9 Science Chapter 2 (Is Matter Around Us Pure) in English. These notes are useful for the students who are going to appear in class 9 board exams.

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Chapter 2: Is Matter Around Us Pure

2.1 What is a Mixture? 🧪

• Mixtures are made up of two or more pure substances mixed together. 🔄  
• For example, seawater, soil, and air are mixtures. 💨🌱  
• A pure substance has only one type of particle. 🔬  
• For example, sugar and salt are pure substances. 🧂

2.1.1 Types of Mixtures 🌈

• Homogeneous mixtures have the same composition throughout. 💧  
• For example, salt or sugar dissolved in water. 🍭  
• Heterogeneous mixtures have physically distinct parts with different compositions. 🪨  
• For example, a mixture of iron filings and salt. 🧲  

2.2 What is a Solution? 🥤

• A solution is a homogeneous mixture of two or more substances. 🧪  
• For example, lemonade and soda water are solutions. 🍹  
• A solution has two parts: solute and solvent. 🧪  
• The solute is the substance that dissolves in the solvent. 🧪  
• The solvent is the substance that dissolves the solute. 🧪  
• For example, in a saltwater solution, salt is the solute and water is the solvent. 🧪  

Properties of a Solution ✨

• A solution is a homogeneous mixture. 🧪  
• The particles in a solution are very small and cannot be seen with the naked eye. 🔬  
• The particles do not scatter a beam of light, so the path of light is not visible in a solution. 🔦  
• The solute particles cannot be separated by filtration. 🧪  
• A solution is stable, meaning the particles do not settle down when left undisturbed. 🧪  

2.2.1 Concentration of a Solution 🧪

• Concentration is the amount of solute present in a given amount of solution. 🧪  
• It can be expressed in different ways, such as mass by mass percentage, mass by volume percentage, and volume by volume percentage. 🧪  
• A saturated solution is a solution that has dissolved the maximum amount of solute at a given temperature. 🧪  
• Solubility is the amount of solute present in a saturated solution at a given temperature. 🧪  
• An unsaturated solution is a solution that has dissolved less than the maximum amount of solute at a given temperature. 🧪  

2.2.2 What is a Suspension? 🥛

• A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. 🧪  
• For example, a mixture of chalk powder and water is a suspension. 🧪  

Properties of a Suspension 🥛

• A suspension is a heterogeneous mixture. 🧪  
• The particles in a suspension are large enough to be seen with the naked eye. 🔬  
• The particles scatter a beam of light, making its path visible (Tyndall effect). 🔦  
• A suspension is unstable, meaning the particles settle down when left undisturbed. 🧪  
• The solute particles can be separated by filtration. 🧪  

2.2.3 What is a Colloidal Solution? 🥛

• A colloidal solution or colloid is a heterogeneous mixture in which the size of solute particles is intermediate between those in a solution and those in a suspension. 🧪  
• For example, milk is a colloidal solution. 🥛  

Properties of a Colloid 🥛

• A colloid is a heterogeneous mixture. 🧪  
• The particles in a colloid are small enough that they cannot be seen with the naked eye. 🔬  
• The particles scatter a beam of light, making its path visible (Tyndall effect). 🔦  
• A colloid is stable, meaning the particles do not settle down when left undisturbed. 🧪  
• The solute particles cannot be separated by filtration but can be separated by centrifugation. 🧪  

2.3 Physical and Chemical Changes 🔄

• Physical changes are changes that do not alter the chemical composition of a substance. 🔄  
• For example, melting, boiling, and changes in state. 💧❄️  
• Chemical changes are changes that alter the chemical composition of a substance. 🔄  
• For example, burning and rusting. 🔥  

2.4 What are the Types of Pure Substances? 🧪

• Elements are pure substances that cannot be broken down into simpler substances by chemical reactions. 🧪  
• For example, oxygen, hydrogen, and iron are elements. 🧪  
• Compounds are pure substances formed when two or more elements chemically combine in a fixed ratio. 🧪  
• For example, water (H2O) is a compound formed from hydrogen and oxygen. 💧  

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