## JAC Class 9 Science Notes Chapter 2 Is Matter Around Us Pure

### JAC Board Class 9th Science Chapter 2 Notes Is Matter Around Us Pure

→ A pure substance consists of a single type of particles.

→ A mixture has more than one substance (element / compound) mixed in any proportion.

→ Mixtures can be separated into pure substances by appropriate separation techniques.

→ A solution is a homogeneous mixture of two or more substances. The major component of a solution is known as the solvent and the minor one is the solute. For example, sugar dissolved in water or alloy of copper and zinc or ethyl alcohol in water.

• Mass percentage of a solution
= $$\frac{\text { Mass of solute }}{\text { Mass of solution }}$$ × 100
• Volume percentage of a solution
= $$\frac{\text { Mass of solute }}{\text { Mass of solution }}$$ × 100

→ Materials which are insoluble in a solvent and have particles which are visible to naked eyes form a suspension. A suspension is a heterogeneous mixture.

→ When solids are dispersed in liquids to form a heterogeneous mixture or an opaque medium, it is called suspension.

→ Colloidal solutions are heterogeneous mixtures where particles of 1 × 109 to 1 × 10-6 m diameter, called dispersed phase, are distributed uniformly in a solvent, called dispersing medium.

→ Difference between true solutions, suspension and colloidal solutions.

 True Solution ColloidalSolution Suspension It is a homogeneous mixture of solute and solvent. It appears to be homogeneous but actually it is a heterogeneous mixture of dispersed phase and dispersing medium. It is a heterogeneous mixture. The solute particles are very small, i.e., less than 109 m in diameter. The solute particles are between 109 and 106 m in diameter. The solute particles are quite large, i.e., larger than 106 m in diameter. Particles of true solution are not visible to naked eye. Particles are not visible to naked eye but can be seen with ultra­microscope. Particles are big enough to be seen by naked eye. The entire solution passes through filter paper. The particles can pass through ordinary filter paper. The particles cannot pass through filter paper. The solute particles do not show Tyndall effect. The particles show Tyndall effect. The particles may or may not show Tyndall effect. The particles do not settle down. The particles do not settle down. The particles may settle due to gravity.

→ Different Types of Colloids

→ Separation of a mixture can be done by hand-picking, sieving, winnowing, sedimentation, decantation, filtration, evaporation, distillation, fractional distillation, centrifugation, crystallisation and chromatography.

→ A physical change brings about a change in the state of matter without change in the composition or chemical nature of the substance.

→ A chemical change brings about a change in chemical properties of matter because one or more substances are transformed into a new substance.

→ Pure substances can be elements or compounds.

→ An element is a form of matter which cannot be broken down by chemical reactions into simpler substances.

→ A compound is a substance composed of two or more different types of elements, chemically combined in a fixed proportion.

→ Properties of a compound are different from its constituent elements whereas a mixture shows the properties of its constituting elements or compounds.