NCERT Solutions For Class 9 Science Chapter 2 Is Matter Around Us Pure

Milk and starch solution will show Tyndall effect because they are colloidal solutions.

Sea water, air and soda water are solutions.

Growth of plant, rusting of iron, cooking of food, digestion of food and burning of a candle are chemical changes.

Every liquid has a characteristic boiling point. Pure water has boiling point of 100 °C (373 K) at 1 atmospheric pressure. Hence, the purity of water can be confirmed by determining its boiling point.

Ice, iron, hydrochloric acid, calcium oxide and mercury fall in the category of pure substance.

Homogeneous mixtures: Soda water, vinegar, filtered tea

Heterogeneous mixtures: Soil, wood

Air is a homogeneous mixture of different gases. However, if some dust or other particles are also present, then air becomes heterogeneous mixture.

Tea can be prepared by following steps:

1. Take some water as solvent in a kettle and boil it for few minutes.
2. Now add one tea spoon sugar, one tea spoon tea leaves and some milk as solute to water. They all together form a solution.
3. Now boil the solution again for few minutes so that sugar dissolves in solution as sugar is soluble in water.
4. Now filter the solution through a strainer. The insoluble tea leaves remain on the strainer as residue and the filtrate is collected in cup.

(a) Saturated solution: A solution in which no more solute can be dissolved at a particular temperature is called as saturated solution. For example: Soft drinks are saturated with carbon dioxide, hence it gives off carbon dioxide through bubbles, the Earth's soil is saturated with nitrogen.

(b) Pure Substance: A substance that shows same characteristics at a given temperature and pressure is called a pure substance. For example distilled water is a pure substance.

(c) Colloid: A colloid is a heterogeneous mixture that consists of particles bigger than that of a solution and smaller than that of suspension. For example: Smoke, butter, milk, etc. are colloids.

(d) Suspension: A suspension is a heterogeneous mixture in which solid is dispersed in liquid. The solute particles in suspension do not dissolve but remain suspended throughout the medium. The particles are large in size and visible to naked eye. For example: Chalk particles, muddy water etc.

\begin{array}{l}\text{(a) Solubility of potassium nitrate at 313 K =}\frac{\text{62}}{\text{100}}\\ \text{100 g of water contains potassium nitrate = 62 g }\\ \therefore \text{ 50 g of water contains potassium nitrate=}\frac{\text{62}}{\text{100}}\text{ x 50 = 31 g }\\ \text{Thus, 31 g potassium nitrate would be needed to}\\ \text{produce a saturated solution of potassium nitrate in }\\ \text{50 g of water at 313 K}\text{.}\end{array}

(b) On cooling the solubility of salt decreases with the falling temperature. Hence, the crystals of potassium chloride will separate out on cooling.

(c)  The maximum amount of the salt which is dissolved in 100 g of water to form a saturated solution at the given temperature is known as solubility. The solubilities of different salts at 293 K in 100g of water are given in column 2 in the table.
 

1. Solubility of potassium nitrate at 293K is 32g.
2. Solubility of sodium chloride at 293K is 36g.
3. Solubility of potassium chloride at 293K is 35g.
4. Solubility of ammonium chloride at 293K is 37g.                                                      

From the above data it is clear that ammonium chloride has the highest solubility at 293 K.

(d) Generally, the solubility of a salt increases with the increasing temperature. However, from the data given in the table, the increase is different for different salts. For example the solubility of potassium nitrate increases appreciably, that of ammonium chloride increases slightly, that of potassium chloride increases marginally while that of sodium chloride almost remains constant.

(a) Sodium chloride from its solution in water: Evaporation
(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride: Sublimation
(c) Small pieces of metal in the engine oil of a car: Filtration
(d) Different pigments from an extract of flower petals: Chromatography
(e) Butter from curd: Centrifugation
(f) Oil from water: Using separating funnel
(g) Tea leaves from tea: Filtration
(h) Iron pins from sand: Magnetic Separation
(i) Wheat grains from husk: Winnowing
(j) Fine mud particles suspended in water: Centrifugation