This question is about weak acids and buffer solutions.
Benzoic acid, C6H5COOH\text{C}_6\text{H}_5\text{COOH}C6H5COOH, is a weak monobasic acid.
Explain what is meant by the term weak monobasic acid.
A buffer solution is prepared by dissolving 0.80 g0.80\text{ g}0.80 g of sodium hydroxide, NaOH\text{NaOH}NaOH, in 400.0 cm3400.0\text{ cm}^3400.0 cm3 of 0.125 mol dm−30.125\text{ mol dm}^{-3}0.125 mol dm−3 benzoic acid.
This buffer solution has a pH of 4.024.024.02 at 25∘C25^\circ\text{C}25∘C.
Calculate the acid dissociation constant, KaK_aKa, of benzoic acid at 25∘C25^\circ\text{C}25∘C.
Assume that the volume of the solution remains constant at 400.0 cm3400.0\text{ cm}^3400.0 cm3 when the sodium hydroxide is dissolved. Give your answer to 3 significant figures.
Ka=K_a = Ka= ........................................ mol dm−3\text{mol dm}^{-3}mol dm−3
When a small volume of water is added to this buffer solution, the pH does not change.
Explain why the pH does not change.