Free Chemical Equilibrium MCQs with Answers
22 Chemical Equilibrium MCQs from Chemistry, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
22 questions · page 3 of 3
21. Which of the following is basic buffer?
- A. NH4OH/NH4Cl
- B. NaOH/NaCl
- C. NaOH/HCl
- D. H2CO3/NaHCO3
Explanation: A basic buffer needs a weak base together with the salt of that base, and ammonium hydroxide with ammonium chloride is the standard example, holding the pH around 9. Carbonic acid with sodium hydrogen carbonate is also a buffer but an acidic one, built from a weak acid and its salt. Sodium hydroxide is a strong base and is fully ionised, so it has no reservoir of un-ionised base and cannot buffer.
Correct answer: NH4OH/NH4Cl22. What happens when H+ is added to ammonium hydroxide and ammonium chloride buffer?
- A. More ammonium hydroxide is formed
- B. Reaction will move reverse
- C. Reaction will move forward
- D. No effect on equilibrium
Explanation: The added hydrogen ions are mopped up by the weak base ammonium hydroxide, which reacts forward to give ammonium ions and water, so the pH barely shifts. This is exactly what buffering means: the reservoir of base neutralises added acid. If alkali were added instead, the ammonium ions from the salt would supply protons to neutralise it.
Correct answer: Reaction will move forward