Question

What is the hydrogen ion concentration of $0.1N$ ${CH}_{3}COOH$ solution. The ionisation constant of ${CH}_{3}COOH$ is $1.8\times {10}^{-5}$. What is the pH of the solution?

Answer 1

Let the degree of dissociation be '$\alpha$'
${CH}_{3}COOH$ is a weak electrolyte; thus
${\alpha }^{2}C=K_a$
${\alpha }^2\times 0.1=1.8\times {10}^{-5}$
$\alpha =1.34\times {10}^{-2}$
$\left[H^{+}\right]=\alpha C=1.34\times {10}^{-3}M$
$pH=-\log \left[H^{+}\right]=-\log 1.34\times {10}^{-3}=2.8729$