1) A 10 mL sample of 0.010 M HCl is diluted by adding distilled water at constant temperature.
Which one of the following items correctly shows the effect of the dilution on the concentrations of H+ and OH– ions
in the solution?
[H+] [OH–]
A. [H+]= decrease [OH–]=decrease
B. [H+]= decrease [OH–]=increase
C.[ H+]=increase [OH–]=decrease
D.[H+]= increase [OH–]=increase

Solution

2) A chemist prepares 0.10 M aqueous solutions of each of the following acids.
Which solution has the lowest pH?
A. CH₃COOH
B. HNO₂
C. HCN
D. HOCl

Solution

3) Barium hydroxide is soluble in water.
The pH at 25 °C of a 0.0050 M solution of Ba(OH)₂ is
A. 2.0
B. 2.3
C. 11.7
D. 12.0

Solution

4) Lactic acid, CH₃CH(OH)COOH, is a weak acid found in milk. The molar mass of lactic acid is 90.0 g mol^–1. In an experiment a student dissolved 4.50 g of lactic acid in 500.0 mL of water.
CH₃CH(OH)COOH(l) + H₂O(l) <=> CH₃CH(OH)COO^–(aq) + H₃O⁺(aq)
a) i) Calculate the equilibrium molar concentration of H₃O⁺ ions in the lactic acid solution.

b) Calculate the pH for the lactic acid solution.

Solution

c). Calculate the percentage ionisation of lactic acid in this experiment.

Solution

d). State one assumption that you made when calculating your answer to part i.

Solution

e) A 1.0 M solution of lactic acid is prepared at 25 °C.
When distilled water is added to this solution
i. the pH will increase decrease no change
ii. the percentage ionisation of the acid will increase decrease no change

iii. Provide an explanation for your answer to part ii.

Solution