આપેલ : $K _{ a }\left( CH _{3} CH _{2} COOH \right)=1.3 \times 10^{-5}$
\(4=5-\log 1.3+\log \frac{\left[ CH _{3} CH _{2} COO ^{-}\right]}{\left[ CH _{3} CH _{2} COOH \right]}\)
\(\log \frac{\left[ CH _{3} CH _{2} COO ^{-}\right]}{\left[ CH _{3} CH _{2} COOH \right]}=\log 1.3-1=\log \frac{1.3}{10}\)
\(\frac{\left[ CH _{3} CH _{2} COO ^{-}\right]}{\left[ CH _{3} CH _{2} COOH ^{-}\right]}=0.13\)