Chemistry
The following figure shows the solubility curves of NaCl, KNO3 and hydrated calcium sulphate.
(a) Identify and label the curves with the salt it represents.
(b) State the factors on which the solubility depends.
(c) Solubility of which salt(s) shows :
(i) Endothermic process
(ii) Exothermic process?
Answer
(a) The labelled curves are shown below:
(b) Solubility of a solid in a solvent depends on the following factors:
- Size of solute particles — The smaller the size of the solute particles, the greater is its total surface area exposed to the solvent. Therefore, greater is the solubility of that solute.
- Stirring — This brings more of the solvent in contact with the solute and thus increases the rate of formation of solution.
- Temperature — The solubility of a gas in a liquid always decreases with rise in temperature. But the solubility of most solids in water usually increases with rise in temperature.
In case of NaCl, solubility increases only a little with increase in temperature.
In case of KNO3, solubility increases considerably with increase in temperature.
In case of calcium sulphate, solubility decreases (after attaining a certain temperature) with further rise in temperature.
(c) (i) In an endothermic process, the solubility of a solute increases with an increase in temperature.
For example: solubility of KNO3 increases with rise in temperature and solubility of NaCl increases only a little with increase in temperature.
(ii) In an exothermic process, the solubility increases on lowering the temperature.
For example: solubility of calcium sulphate in water decreases on increasing the temperature.
Related Questions
Explain:
(a) The use of lead pipes for drinking water supply is being discontinued.
(b) Chalk hills dissolve in rain water.
(c) Hard water is unfit for boilers.
(d) Iron chloride forms a saturated solution when exposed to the atmosphere.
(e) A bottle containing concentrated H2SO4 should be stoppered.
Some salts while crystallising out from their solutions, combine with a definite quantity of water. Some of these salts lose this water on exposure to dry air. Certain water soluble substances, when exposed to atmosphere at ordinary temperatures, absorb moisture from atmospheric air forming a saturated solution.
(a) State the term used for a 'definite quantity of water' combined with a salt.
(b) What type of salts lose their water molecules ? Give two examples.
(c) Table salt forms a solution on exposure to air during rainy season. Explain.
(d) How can pure sodium chloride be obtained from the above table salt solution in (c) ?
Assertion (A): Water is a universal solvent.
Reason (R): Water dissolves all substances except noble metals and glass.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Assertion (A): A saturated solution becomes unsaturated on heating.
Reason (R): More amount of solute can dissolve in a solvent upon heating.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.