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Acids, bases and equilibrium
8 MDCAT Chemistry questions with answers and explanations.
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What is the pH of 0.01 M hydrochloric acid?
- 1 1
- 2 2
- 3 7
- 4 12
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Correct answer: 2
HCl is a strong acid, so [H+] = 0.01 = 10^-2 and pH = 2.
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What is the pH of 0.001 M sodium hydroxide at 25 degrees C?
- 1 3
- 2 10
- 3 11
- 4 13
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What is the conjugate base of H2SO4?
- 1 SO4 2-
- 2 HSO4-
- 3 H3SO4+
- 4 OH-
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Correct answer: HSO4-
When H2SO4 gives away one proton it becomes HSO4-, which is its conjugate base.
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For N2 + 3H2 <-> 2NH3, increasing the pressure shifts the equilibrium:
- 1 To the left
- 2 To the right
- 3 It does not change
- 4 Only if a catalyst is added
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Correct answer: To the right
The forward reaction reduces 4 moles of gas to 2 moles. Higher pressure favours the side with fewer gas moles, so it shifts right.
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A buffer solution is made of:
- 1 A strong acid and a strong base
- 2 A weak acid and its salt
- 3 Two salts of strong acids
- 4 Pure water and a salt
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Correct answer: A weak acid and its salt
A weak acid and its conjugate base resist large changes in pH when small amounts of acid or base are added.
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What is the pOH of a solution whose pH is 4 at 25 degrees C?
- 1 4
- 2 7
- 3 10
- 4 14
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Which expression gives the solubility product Ksp of AgCl?
- 1 [AgCl]
- 2 [Ag+] x [Cl-]
- 3 [Ag+] / [Cl-]
- 4 [Ag+] + [Cl-]
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Correct answer: [Ag+] x [Cl-]
For a sparingly soluble salt, Ksp is the product of the ion concentrations at saturation.
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A larger value of Ka means that the acid is:
- 1 Weaker
- 2 Stronger
- 3 More basic
- 4 Unable to ionise
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Correct answer: Stronger
Ka measures how far an acid ionises. A larger Ka means more ionisation, so a stronger acid.