NCERT SOLUTIONS OF CLASS 9th CHEMISTRY CHAPTER 2 IS MATTER AROUND US PURE ?

1. Which separation techniques will you apply for the separation of the following?

(a) Sodium chloride from its solution in water.

(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.

(c) Small pieces of metal in the engine oil of a car.

(d) Different pigments from an extract of flower petals.

(e) Butter from curd.

(f) Oil from water.

(g) Tea leaves from tea.

(h) Irons pins from sand.

(i) Wheat grains from husk.

(j) Fine mud particles are suspended in water.

ANS: 

(a) Evaporation

(b) Sublimation

(c) Filtration

(d) Chromatography

(e) Centrifugation

(f) Separating funnel

(g) Filtration

(h) Magnetic separation

(i) Winnowing or Gravity              separation

(j)  Filtration

2. Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate, and residue.

 ANS: Take 100 ml of water which acts as a solvent. Boil water on a gas stove or any other appliance. Add one teaspoon of sugar which acts as solute. Sugar gets dissolved in water and forms a solution. Now add about half a teaspoon of tea leaves which are insoluble in water. Boil the contents for 4-5 minutes and add half a cup of milk and allow it to boil again for 2-3 minutes. Filter the tea with the help of a sieve. Tea leaves will be left as residue while tea will be obtained as filtrate.

3. Pragya tested the solubility of three different substances at different temperatures and collected the data as given below.

(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313 K?

ANS: Solubility of potassium nitrate at 313 K = 62 g\100 g of water.100 g of water contains potassium nitrate = 62 g50 g of water will contain potassium nitrate = 62\100*50=31 g therefore, 31 g of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 g of water at 313 K(b) Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to cool at room temperature.

 

(b) What would she observe as the solution cools? Explain.

ANS: On cooling the saturated solution of potassium chloride in water at 353 K to room temperature, crystals of potassium chloride will be formed.

(c) What is the effect of change of temperature on the solubility of a salt?

ANS: The solubility of salts increases with an increase in temperature.

4.  Explain the following by giving examples:

(a) Saturated solution

(b) Pure substance

(c) Colloid

(d) Suspension

ANS: (a) Saturated solution. A solution in which no more solute can be dissolved in a given amount of solvent at a particular temperature is called a saturated solution. For example, if we dissolve 40 g sodium chloride in 100 g of water at 293 K, it will form a saturated solution because the solubility of sodium chloride at 293 K is 36 g per 100 g of water.

(b) Pure substance. A substance made up of only one kind of atoms or molecules is called a pure substance. A pure substance has the same color, taste, and texture at a given temperature and pressure. A pure substance also has a fixed melting and boiling point at a constant pressure. For example, hydrogen gas, sodium chloride, water, etc.

(c) Colloid. A substance is said to be a colloid if its particle size lies between 1 to 100 NM. A colloidal solution is heterogeneous and consists of two phases i.e., dispersed phase (colloidal particles) and dispersion medium in which colloidal particles are suspended. For example, a colloidal solution of Sulphur or starch, milk, etc.

(d) Suspension. It is a heterogeneous mixture in which the particles of the solute do not dissolve but remain suspended throughout the bulk of the solvent. The size of the suspension particles is more than   10^-7 m. For example, chalk powder in water is a suspension.

5. Classify each of the following  as a homogeneous or heterogeneous mixture:

ANS: Soda water: Homogeneous mixture

Wood: Heterogeneous mixture

Vinegar: Homogeneous mixture

Air: Homogeneous mixture

Filtered tea: Homogeneous mixture

6. How would you confirm that a colorless liquid given to you is pure water?

ANS: Determine the boiling point of the given liquid. If its boiling point is 100 ^o C at atmospheric pressure, then it is pure water because water has a boiling point of 100 ^o C.

7. Which of the following materials falls in the category of a " pure substance "?

(a) Ice                      

(b) Milk 

(c) Iron                     

(d) Hydrochloric acid 

(e) Calcium oxide    

(f) Mercury

(g) Brick                  

(h) Wood

(i) Air

ANS: 

(a) Ice

(c) Iron

(d) Hydrochloric acid      

(f) Mercury

These are the pure substances from the list given above in the question.

8. Identify the solutions among the following mixtures.

(a) soil               

(b) Seawater

(c) Air                

(d) Coal

(e) Soda water

ANS: The solutions in the above-given list are as under:(b) Seawater              (e) Soda water

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