EXERCISES: ( Text book )
1: Which separation techniques will 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) Iron pins from sand.
(i) Wheat grains from husk.
(j) Fine mud particles suspended in water.
Ans: (a) Crystallization or Evaporation. (b) Sublimation.
(c) Centrifugation or Sedimentation. (d) Chromatography.
(e) Centrifugation. (f) Separating funnel.
(g) Hand-picking. (h) Magnetic separation.
(i) Winnowing. (j) Centrifugation
2: Write the steps you would use for making tea. Use the words – solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.
Ans: Take the solvent, water, in a kettle. Heat it. When the solvent boils, add the solute, milk. Milk and water forms a solution. Then pour some tea leaves over a sieve. Pour slowly hot solution of milk over tea leaves. Colour of tea leaves goes into solution as filtrate. The remaining tea leaves being insoluble remains as residue. Add requisite sugar which dissolves and the tea is ready.
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).
Temperature in K
(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.
(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.
(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature.
(d) What is the effect of change of temperature on the solubility of a salt.
Ans: 1. At 313 K, Potassium nitrate saturated solution or 100 grams of water = 62g
∴ Potassium nitrate for saturated solution of 50 grams of water = 31 g
2. Some amount of dissolved Potassium Chloride will reappear as undissolved solid as solubility of solute decreases with the decrease of temperature.
3. Solubility of each salt at 393 K are as follows: Potassium nitrate 32 Sodium chloride 36 Potassium chloride 35 Ammonium chloride 37 Ammonium chloride salt has the highest solubility at this temperature.
4. Solubility of salt increases with the increase in temperature.
4: Explain the following giving examples.
(a) Saturated solution, (b) Pure substance, (c) Colloid, (d) Suspension.
Ans: (a) Saturated Solution: A solution in which no more of the solid (solute) can be dissolved at a given temperature is called a saturated solution. Suppose 50 gm of a solute is the maximum amount that can be dissolved in 100 gm water at 298 K. Then 150 gm of solution so obtained is the saturated solution at 298 K.
(b) Pure Substance: Pure substances always have the same colour, taste and texture at a given temperature and pressure. For example, Distill water.
(c) Colloid: A heterogeneous mixture where size of particles lies between 1 – 100 nm and cannot be seen by naked eyes. e.g. smoke, milk, fog, cloud etc.
(d) Suspension: A ‘suspension’ is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. Eg: muddy water, saw dust- water mixture.
5: Classify each of the following as a homogeneous or heterogeneous mixture: soda water, wood, air, soil, vinegar, filtrated tea.
Ans:
Homogeneous mixture − soda water, air, vinegar, filtered tea.
Heterogeneous mixture − wood, soil.
6: How would you confirm that a colourless liquid given to you is pure water.
Ans: Every liquid has a characteristic boiling point at 1 atmospheric pressure. If the given colourless liquid boils exactly at 373 K at 1 atmospheric pressure, then it is pure water. If the boiling point is different, then the water is contaminated.
7: Which of the following materials fall 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: Ice, Iron, Hydrochloric acid, Calcium oxide and Mercury are pure substances.
8: Identify the solutions among the following mixtures.
(a) Soil (b) Sea water (c) Air (d) Coal (e) Soda water.
Ans: Solutions among the following mixtures are sea water and soda water.
9: Which of the following will show “Tyndall effect”.(a) Salt solution(b) Milk(c) Copper sulphate solution(d) Starch solution.
Ans: (b) and (d) are colloids and will show Tyndall Effect.
10: Classify the following into elements, compounds and mixtures.
(a) Sodium (b) Soil (c) Sugar solution (d) Silver (e) Calcium carbonate (f) Tin
(g) Silicon (h) Coal (i) Air (j) Soap (k) Methane (l) Carbon dioxide (m) Blood
Ans: Elements − sodium, silver, tin, silicon. Compounds − calcium carbonate, methane, carbon dioxide Mixtures − soil, sugar solution, coal, air, soap, blood.
11: Which of the following are chemical changes.
(a) Growth of a plant (b) Rusting of iron (c) Cooking of food (d) Mixing of iron filings and sand (e) Digestion of food (f) Freezing of water (g) Burning of a candle.
Ans: Following are Chemical changes.
(a) Growth of a plant (b) Rusting of iron (c) Cooking of food
(d) Digestion of food (e) Burning of a candle.