Explain how to prepare 1L of a buffer at pH 7.4 using 1M hypochlorous acid (Ka = 3.5 x 10-8) and a 1 M NaOH solution. Indicate the volume of hypochlorous acid and sodium hydroxide to use.

Answer 1

pka=-log(3.5 x 10^-8)=7.46

pH=pKa+ log ([A-]/[HA]),

solve for [A-]/[HJA]

10^(pH-pKa)=[A-]/[HJA]=0.879

1-0.879=0.121=[A-]

As Dr. Bob222 would say, add 121mL of NaOH solution to a volumetric flask, and add HClO to the 1,000mL mark of a 1,000mL volumetric flask.

Answer 2

Replace HJA with HA in the above post.