Question

What is the pH of 0.40M of H3PO4? Assume full dissociation.

Answer 1

$H_3PO_4 ⇌ H+ (aq) + H_2PO_4$

K_a = 7.2 x 10^-3

After dissociation $H_3PO_4 ⇌ H+ (aq) + H_2PO_4$

$\implies$

[H⁺] = 0.16

$P_H = - log[H^+]$

$P_H =0.79$