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Chapter - 2, Is matter around us pure?, Science, Class 9

The document explains the concepts of pure substances, mixtures, solutions, and various types of mixtures, including homogeneous and heterogeneous mixtures. It details the properties of solutions, suspensions, and colloids, along with methods for separating mixture components. Additionally, it distinguishes between physical and chemical changes with relevant examples.

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CHAPTER - 2 IS MATTER AROUND US PURE? BY SHIVAM PARMAR (ENTREPRENEUR)
PURE SUBSTANCES • Pure substances are elements or compounds. • They are made up of only one kind of entity. • They cannot be broken down into simpler entities by chemical or physical methods. • They have a fixed composition. • Example: Diamond, carbon dioxide. • Matter can be classified into two types of substances – Pure substances and Mixtures
Mixtures are formed by just mixing two or more pure substances (components) such that each substance retains its own chemical identity. WHAT IS A MIXTURE?
1. HOMOGENEOUS MIXTURE • A mixture which has a uniform composition throughout is called a homogeneous mixture or solution. • Examples: sugar in water, salt in water.
2. HETEROGENEOUS MIXTURE • A mixture which contains physically distinct parts and has a non-uniform composition is called a heterogeneous mixture. • Examples: Mixture of sodium chloride (salt) and iron filings, sand and sugar.
DIFFERENCEBETWEEN MIXTURES AND COMPOUNDS
SOLUTION • A solution is homogeneous mixture of two or more substances. • Examples – Lemonade, soda water • In a solution there is homogeneity at the particle level. • Alloys – Solid solutions (mixtures of metals or a mixture of a metal and another element) • Air – Gaseous solutions • A solution has a solvent and solute as its components. • Solute (lesser quantity) • Solvent (larger quantity)
PROPERTIES OF SOLUTION • Homogeneous mixture. • Particles of a solution are smaller than 1nm (nano-meter). • Particles do not scatter a beam of light(path of light is not visible). • Solute particles cannot be separated by the process of filtration.
DIFFERENT TYPES OF SOLUTIONS • Dilute – A solution in which the concentration of the solute is much less than that of the solvent. For Example, If we mix 1gm of salt in 500 ml of water, the salt solution thus obtained will be diluted. If we keep on adding the solute in a solution there comes a point when no more solute dissolves in the solution. This is called the Saturation Point of a Solution.
• Unsaturated Solution – A solution, in which we can add more amount of solute as it has not achieved its saturation level yet, is called an Unsaturated Solution. A dilute solution can be called as an Unsaturated Solution.
• Concentrated Solution – A solution with a large amount of solvent is called a Concentrated Solution. • Saturated Solution – A solution in which no more solute can be added since it has already dissolved the maximum amount of solute it can is called a Saturated Solution.
CONCENTRATION • Concentration refers to the amount of a substanceper defined space or can be defined as the ratio of solute in a solution to either solvent or total solution. • To calculate the concentration consider the formulae below: • Mass by mass percentage = (Mass of solute / Mass of solution) X 100 • Mass by Volume percentage = (Mass of solute / Volume of solution) X 100 • Volume by volume percentage = (Volume of solute / Volume of solution) X 100
SUSPENSION • A suspension is formed when two or more substancesare mix in a non-uniform manner. • Properties of Suspensions: • A suspension is a heterogeneous mixture. • The particles of a suspension can be seen by the naked eyes. • Particles of a suspension scatter a beam of light passing through it (visible path). • The particles of suspension tend to settle down when left undisturbed. Then, they can be separated using filtration.
COLLOIDAL SOLUTION • A colloidal solution or a colloid is a uniform solution of two or more substances. • Due to relatively smaller size of particles, as compared to that of a suspension, the mixture appears to be homogeneous, but it is a heterogeneous mixture. For example - milk.
PROPERTIES OF COLLOIDS • Colloids are heterogeneous in nature. • The particles of a colloid cannot be seen through naked eyes. • The particles scatter a beam of light passed through a colloid and produce Tyndall effect.
Colloids are stable in nature. The particles of colloids do not settle down if left undisturbed. We cannot separate the particles of a colloid through filtration. We use a method called Centrifugation to separate the particles of a colloid.
• When a beam of light is passed through a colloid the particles of the colloid scatter the beam of light and we can see the path of light in the solution. • For Example, when a ray of light enters a dark room it is scattered by the dust particles present in the air and we can see the path of light clearly. TYNDALL EFFECT
COMPONENTS OF COLLOID Dispersed Phase – The dispersed particles or the solute-like components in a colloid. Dispersing Medium – The substance in which these solute- like particles are added.
Heterogeneous mixtures can be separated into their respective constituents by simple physical methods • Filtration • Hand-picking • Sieving SEPARATINGTHE COMPONENTS OF A MIXTURE
# The components of a mixture can be separated from each other using several other techniques like • Evaporation • Centrifugation
• Separation of two immiscible liquids • Sublimation
• Chromatography
• Distillation / Fractional Distillation • Crystallization
PHYSICAL CHANGE • The interconversion of states is a physical change because these changes occur without a change in composition and no change in the chemical nature of the substance. • Example – Melting of ice, cutting of trees.
CHEMICAL CHANGE • One substance reacts with another to undergo a change in the chemical composition. Chemical change brings change in the chemical properties. • Example – Burning of paper and wood, Souring of milk.
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