Ionic equilibria and pH

Written by Dr. Ayesha Nadeem (Chemistry)

NET · Chemistry · 5 questions

Name: ____________________ Date: ____________

Adding sodium chloride to a saturated solution of silver chloride will make the silver chloride:
- A More soluble
- B Turn into a gas
- C Less soluble
- D Unaffected
A buffer contains equal concentrations of acetic acid and acetate ion. The pKa of acetic acid is 4.76. What is the pH?
- A 7.00
- B 9.52
- C 2.38
- D 4.76
What is the pH of 0.05 M sulphuric acid, taking both protons as fully ionised?
- A 0.05
- B 1
- C 1.3
- D 2
What is the value of the ionic product of water, Kw, at 25 degrees C?
- A 1 x 10^-1
- B 1 x 10^14
- C 1 x 10^-14
- D 1 x 10^-7
An aqueous solution of ammonium chloride is:
- A Neutral
- B Basic
- C Strongly basic
- D Acidic

Answer key

1. C, 2. D, 3. B, 4. C, 5. D

This is the common ion effect. Extra chloride ions push the equilibrium towards the solid.
When [A-] = [HA], the log term is zero and pH = pKa = 4.76.
[H+] = 2 x 0.05 = 0.1 M, so pH = 1.
Kw = [H+][OH-] = 10^-7 x 10^-7 = 10^-14 at 25 degrees C.
It is a salt of a strong acid and a weak base. The ammonium ion releases protons in water.