CHEMISTRY [3 Mark Question Answer]

(a) oceans–oceans hold about 96.5 percent of all Earth’s water
(b) glaciers and ice caps– About 2.1% of all of Earth’s water is frozen in glaciers
(c) in streams and rivers — only 0.3% left for lakes, rivers, streams, and swamps.

(a) The solubility of a solid in a solution increases with increasing temperature. If the temperature of a saturated solution is increased, the solution will become unsaturated. Thus, the temperature plays an important role in specifying whether a solution is saturated or not.
(b) two ways, by which a saturated solution can be changed to unsaturated solution.
• On heating, a saturated solution becomes unsaturated and more solute can be dissolved in the solution.
• By adding more solvent, a saturated solution can be made unsaturated.

(i) Boiling--boiling the water causes the precipitation of solid calcium carbonate or solid magnesium carbonate. This removes the calcium ions or magnesium ions from the water, and so removes the temporary hardness
(ii) Addition of washing soda--Permanent hardness of water is due to dissolved salts of chlorides and sulphates of calcium and magnesium which can be removed by adding sodium carbonate (Na2CO3) (washing soda or soda ash) which reacts with these dissolved salts to form insoluble carbonates that can be removed by filtration and then water becomes soft