Solutions Exam 1 and Problem Solutions

Solutions Exam 1 and Problem Solutions

1. X solid has ionic structure and solubility of it increases with increasing temperature. If solubility of X in water at 15 0C is 20g X/100 g water, find which ones of the following statements are true for solution prepared by using 10 g X and 50 g water at 15 0C;

I. This solution conducts electric current

II. If 30 g water and 5 g X are added to solution under constant temperature, some amount of X stays undissolved.

III. If solution is cooled from 15 0C to 10 0C, some amount of  crystallize.


I . Since structure of X is ionic, when it dissolves in water it decompose into its ions and we know that solutions including ions conduct electric current. I is true.

II. After addition of water and X we have;

Mass of water=50+30=80 g

Mass of X=10+5=15 g

At 15 0C;

100g water dissolves 20 g X

80g water dissolves ? g X


?=16 g X can be dissolved in 80 g water. Since we have 15 X, solution is unsaturated, so all X is dissolved. II is false.

III. At 15 0C;

100 g water dissolves 20 g X

50 g water dissolves ? g X


?=10 g X can be dissolved.

This solution is saturated. Thus, since it is endothermic solution ( solubility increases with increasing temperature), when we cool it some X crystallize. III is true.

2. There are equal amounts of water in given containers.

Solubility Example

Find relation between solubility of CO2 gas in water under given conditions.


Solubility of CO2 in water increases with increasing partial pressure of CO2 and decreasing in the temperature. I and II has equal temperature but partial pressure of CO2 in II is larger than I. So, solubility of II is larger than I.

I and III has equal partial pressure, but temperature of I is lower than III, so solubility of I is larger than III.Relation between them become;

II > I > III

3. Graph given below shows relation between solubility and temperature of X and Y solids.

Solubility Example

Which one of the following statements are false for this graph?

I. Dissolution of X in water is exothermic

II. When X solid and X-water solution in equilibrium is heated, amount of solid X decreases

III. When saturated Y solution is heated, it becomes unsaturated.


I . Since solubility of X decreases with increasing temperature, it is exothermic. I is true.

II. Since solution of X in water is exothermic, when solution is heated, some amount of X crystallize so amount of X solid increases. II is false.

III. As you can see from the graph, solubility of Y in water is endothermic. Increasing temperature increases its solubility and saturated solution becomes unsaturated. III is true.

4. 25 g salt and 125 g water are mixed and solution is prepared. Find concentration of solution by percent mass.


Mass of Solute: 25 g

Mass of Solution: 25 + 125 = 150 g

125 g solution includes 25 g solute

100 g solution includes X g solute


X=20 g %

Or using formula;

Percent by mass=25.100/125=20 %

5. How much water must be vaporized from 0,4 molar 200 mL H2SO4 solution to make it 1,6 molar at same temperature?


V=200 mL = 0,2 L

Mole of H2SO4;


n=M.V, M=n/V

1,6 molar=0,08/V=0,05L=50mL

200-50=150mL water must be vaporized.