Question

Which weak acid should be used to create a buffer at pH= 4.7

		"Carbonic, H2CO3, Ka = 4.30×10–7"
		"Hypochlorous Acid, HOCl, , Ka = 3.50×10–8"
		"Hypobromous Acid, HOBr, Ka = 2.00×10–9"
		"Chloroacetic Acid, CClH2O2H, Ka = 1.36×10–3"
		"Lactic Acid, C3H6O2, Ka = 1.38×10–4"
		"Acetic Acid, CH3O2H, Ka = 1.75×10–5"

Answer 1

For base buffer pH of the buffer should be closest to pKa of the acid.

So,
pKa should be closest to 4.7

Given:
pKa = 4.7

use:
pKa = -log Ka
4.7 = -log Ka
Ka = 2.0*10^-5

SO, Ka of the acid should be closest to 2.0*10^-5

This is true for acetic acid

Answer: acetic acid