Chemistry
A solution of a solid in a liquid (such as water) can be prepared by adding the solid to water with constant stirring at a particular temperature. If the addition process is continued, a stage is ultimately reached in the dissolution process when no more of the solid dissolves. The solution at this stage is said to be saturated. The solubility of a solute is always expressed with respect to the saturated solution. It may be defined as the maximum amount of the solute that can be dissolved in 100 g of the solvent to form a saturated solution at a given temperature.
The solution becomes unsaturated if the temperature is increased. In case the temperature is decreased, the solution becomes supersaturated and crust of the solute gets deposited on the surface.
(a) A student studied the solubility of three substances in water at different temperatures and collected the following data.
| Temperature (°C) | 286 | 300 | 320 | 350 |
|---|---|---|---|---|
| Substance dissolved | Solubility | |||
| X | 20 | 24 | 26 | 30 |
| Y | 30 | 36 | 48 | 54 |
| Z | 24 | 20 | 18 | 14 |
The correct order of the solubilities of these substances in water is :
(i) Y > X > Z
(ii) X > Y > Z
(iii) Z > X > Y
(iv) Y > Z > X
(b) 10 g of a solute is dissolved in 250 g of a solvent. The solubility of the solute is:
(i) 4 g
(ii) 40 g
(iii) 10 g
(iv) 20 g
(c) A saturated solution becomes unsaturated by :
(i) Heating the solution
(ii) Cooling the solution
(iii) Adding more of the solute
(iv) Adding more of the solvent
(a) (i) and (iii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (iii) and (iv)
(d) Solubility of a solute in a solvent may be defined as:
(i) Dissolution of 1 g of solute in one kg of solvent at a given temperature.
(ii) Dissolution of 1 g of solute in 100 g of the solvent at a given temperature.
(iii) Dissolution of 1 g of solute in 100 mL of the solvent at a given temperature.
(iv) The maximum amount of solute which can be dissolved in 100 g of the solvent to form a saturated solution at a given temperature.
Water
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Answer
(a) Y > X > Z
Reason - Solubility is increasing with increase in temperature in case of X and Y but solubility is decreasing with increase in temperature in case of Z.
Y is highest and Z is the lowest with X in middle.
Therefore, Y > X > Z is the correct option.
(b) 10 g solute in 250 g solvent
Solubility =
= 4 g
(c) (i) and (iv)
Reason - Heating the solution increases the solubility.
Adding more of the solvent so that more solute can dissolve.
Cooling the solution decreases the solubility. A saturated solution cannot dissolve more solute at that temperature. Any extra solute added will simply remain undissolved at the bottom.
(d) The maximum amount of solute which can be dissolved in 100 g of the solvent to form a saturated solution at a given temperature.
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