If 1 mM solution of ethylamine produces pH = 9, then the ionization constant (Kb) of ethylamine

Question

If 1 mM solution of ethylamine produces \( \mathrm{pH}=9\), then the ionization constant \(\left(\mathrm{K}_{\mathrm{b}}\right)\) of ethylamine is \(10^{-x}\). The value of x is _____ (nearest integer).

[The degree of ionization of ethylamine can be neglected with respect to unity.]

Answer 1

Answer is : 7

pOH + pH = 14

pOH = 14 - 9

pOH = 5

\([OH^-] =10^{-5}\ m\) 

\([OH^-] = \sqrt{K_b.C}\) 

C = concentration of weak base = 1 mM = \(10^{-3} \ M\)

\(10^{-5} = \sqrt{K_b\times 10^{-3}}\)

\(10^{-10} = K_b\times 10^{-3}\)

\(K_b = 10^{-7}\)

\(x = 7\)