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Question:

Addition of sodium hydroxide solution to a weak acid (HA) results in a buffer of pH=6. If the ionization constant of HA is 10⁻⁵, the ratio of salt to acid concentration in the buffer solution will be:

1:10

10:1

5:4

4:5

Solution:

Ka=10⁻⁵
pKa=-logKa=-log10⁻⁵=5
pH=pKa+log[salt]/[acid]
6=5+log[salt]/[acid]
1=log[salt]/[acid]
[salt]/[acid]=10¹
Hence, the ratio of salt to acid concentration is 10:1. Therefore, the correct option is (B).