Acids, bases and equilibrium

Written by Dr. Ayesha Nadeem (Chemistry)

MDCAT · Chemistry · 11 questions

Name: ____________________ Date: ____________

What is the pH of 0.01 M hydrochloric acid?
- A 12
- B 7
- C 1
- D 2
What is the pH of 0.001 M sodium hydroxide at 25 degrees C?
- A 11
- B 10
- C 3
- D 13
What is the conjugate base of H2SO4?
- A SO4 2-
- B H3SO4+
- C OH-
- D HSO4-
For N2 + 3H2 <-> 2NH3, increasing the pressure shifts the equilibrium:
- A To the left
- B To the right
- C It does not change
- D Only if a catalyst is added
A buffer solution is made of:
- A A strong acid and a strong base
- B Pure water and a salt
- C Two salts of strong acids
- D A weak acid and its salt
What is the pOH of a solution whose pH is 4 at 25 degrees C?
- A 14
- B 4
- C 7
- D 10
Which expression gives the solubility product Ksp of AgCl?
- A [Ag+] x [Cl-]
- B [Ag+] / [Cl-]
- C [AgCl]
- D [Ag+] + [Cl-]
A larger value of Ka means that the acid is:
- A Weaker
- B Stronger
- C More basic
- D Unable to ionise
The pH of a solution with a hydrogen ion concentration of 1 × 10⁻³ mol/dm³ is:
- A 11
- B 3
- C −3
- D 7
A buffer solution is one that:
- A Changes colour at its end point
- B Resists a change in pH when small amounts of acid or base are added
- C Has a pH of exactly 7
- D Contains only a strong acid
For the reaction N₂ + 3H₂ ⇌ 2NH₃ (exothermic), increasing the pressure shifts the equilibrium:
- A Towards ammonia
- B Towards nitrogen and hydrogen
- C Not at all
- D Towards the side with more moles of gas

Answer key

1. D, 2. A, 3. D, 4. B, 5. D, 6. D, 7. A, 8. B, 9. B, 10. B, 11. A

HCl is a strong acid, so [H+] = 0.01 = 10^-2 and pH = 2.
[OH-] = 10^-3, so pOH = 3 and pH = 14 - 3 = 11.
When H2SO4 gives away one proton it becomes HSO4-, which is its conjugate base.
The forward reaction reduces 4 moles of gas to 2 moles. Higher pressure favours the side with fewer gas moles, so it shifts right.
A weak acid and its conjugate base resist large changes in pH when small amounts of acid or base are added.
pH + pOH = 14, so pOH = 14 - 4 = 10.
For a sparingly soluble salt, Ksp is the product of the ion concentrations at saturation.
Ka measures how far an acid ionises. A larger Ka means more ionisation, so a stronger acid.
pH = −log[H⁺] = −log(10⁻³) = 3.
A buffer contains a weak acid and its salt (or a weak base and its salt) and keeps the pH almost constant.
Four moles of gas on the left become two on the right, so higher pressure favours ammonia.