Question

Which of the following solutions would be able to act as a buffer?

a) 15.0mL of 1.0M NaOH and 25.0mL of 1.0M HC₂H₃O₂ (This is the correct answer)

b) 30mL of 1M NaOH and 25mL of 1M HC₂H₃O₂

_{c) 25mL of 1M NaOH and 25mL of 1M}HC₂H₃O₂

_{d) 20mL of 1M NaOH and 25mL of 1M HBr}

Question: Why is A the correct answer, I was given the explaination that the strong should be the limiting reagent but D has the same outcome?

Answer 1

The solution will act as an acid buffer if the solution contains the mixture of a weak acid and the salt of the conjugate base of that weak acid.

a) Here after addition of 15mL of 1.0M NaOH to 25.0mL of 1.0M C2H3O2 there will be excess weak acid i.e. C2H3O2 and the salt NaC2H2O2. So this mixture will act as an acid buffer.

b) In case of option b there wil be salt but there will be excess base in the mixture. Hence it will not act as a buffer solution.

c) In case of option c there will only be the salt NaC2H2O2 but there is no weak acid in it. So it will also not act as a buffer.

d) In case of option d both the acid and base are strong. There will be salt NaBr and excess strong acid HBr. HBr is a strong acid that is why this mixture will not act as a buffer.