Class 9 Science

# Mixture

## NCERT Solution

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

1. Sodium chloride from its solution in water.
2. Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.
3. Small pieces of metal in the engine oil of a car.
4. Different pigments from an extract of flower petals.
5. Butter from curd.
6. Oil from water.
7. Tea leaves from tea.
8. Iron pins from sand.
9. Wheat grains from husk.
10. Fine mud particles suspended in water.

Answer: (a) Evaporation (b) Sublimation (c) Magnetic separation (d) Chromatography (e) Filtration (f) Separating funnel (g) Filtration (h) Magnetic separation (i) Winnowing (j) Sedimentation and decantation

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

Answer: Dissolve sugar in water by boiling, Sugar is soluble in water. Mix milk in water. Milk is miscible in water. Add tea leaves to boiling water. Tea leaves are insoluble in water. After boiling the mixture for a few minutes, separate tea leaves by filtration. The liquor in cup is the filtrate, while tea leaves in the strainer are residue.

Question 3. Pragya tested the solubility of three different substances at different temperatures and collected the data as given below (results are given in the following table, as grams of substance dissolved in 100 grams of water to form a saturated solution).

Substance DissolvedTemperature in K
283293313333353
Potassium nitrate213262106167
Sodium chloride3636363737
Potassium chloride3535404654
Ammonium chloride2437415556

(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?

Answer: Since 62 g of potassium nitrate is required to make saturated solution in 100 g water at 313 K. Hence, half of it, i.e. 31 g of potassium nitrate shall be required to make saturated solution 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. What would she observe as the solution cools? Explain.

Answer: We know that maximum concentration of a solute decreases with decrease in temperature. Hence, excess amount of potassium chloride will be seen settling down at the bottom.

(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?

Answer: Ammonium chloride has the highest solubility (37 g) at 293K. It is followed by sodium chloride (36 g), potassium chloride (35 g) and potassium nitrate (32 g).

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

Answer: Solubility of salt increases with increase in temperature.

Question 4. Explain the following giving examples.

(a) saturated solution

Answer: A solution in which no more solute can be dissolved at the given temperature is called a concentrated solution at that temperature.

(b) pure substance

Answer: If the components of a substance cannot be separated by any physical method, the substance is called a pure substance.

(c) Colloid

Answer: It is a heterogenous mixture in which particles are too small to be seen by naked eye, but are large enough to cause scattering of light to produce Tyndall effect.

(d) Suspension

Answer: It is a heterogeneous mixture in which particles are large enough to remain suspended in the medium. The particles settle down when the mixture is left undisturbed for some time.

Question 5. Classify each of the following as a homogeneous or heterogeneous mixture. (soda water, wood, air, soil, vinegar, filtered tea.)

Answer: Homogeneous Mixture (Soda water, air, vinegar, filtered tea) Heterogeneous mixture (wood, soil)

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

Answer: If the given liquid starts boiling at 100°C at normal temperature and pressure, it is pure water. It is important to keep in mind that pure substances have fixed boiling point at normal temperature and pressure.

Question 7. Which of the following materials fall in the category of a “pure substance”? (Ice, Milk, Iron, Hydrochloric acid, Calcium oxide, Mercury, Brick, Wood, Air.)

Answer: Iron, Hydrochloric acid, Calcium oxide, Mercury

Question 8. Identify the solutions among the following mixtures. (Soil, Sea water, Air, Coal, Soda water)

Answer: Sea water, soda water, air

Question 9. Which of the following will show “Tyndall effect”?

1. Salt solution
2. Milk
3. Copper sulphate solution
4. Starch solution.

Answer: (b) Milk and (d) Starch solution

Question 10. Classify the following into elements, compounds and mixtures. (Sodium, Soil, Sugar solution, Silver, Calcium carbonate, Tin, Silicon, Coal, Air, Soap, Methane, Carbon dioxide, Blood)

Answer: Elements (sodium, silver, tin, silicon)
Compound (calcium carbonate, methane, carbon dioxide)
Mixture (Soil, Sugar solution, Coal, Air, Soap, Blood)

Question 11. Which of the following are chemical changes? (Growth of a plant, Rusting of iron, Mixing of iron filings and sand, Cooking of food, Digestion of food, Freezing of water, Burning of a candle.)

Answer: Growth of a plant, Rusting of iron, Cooking of food, Digestion of food, Burning of a candle