Certain polyprotic salts contain amphiprotic anions that can undergo both ionization to release and — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

$NaHCO_3$, $NaHS$, and $NaH_2PO_4$ contain amphiprotic anions ($HCO_3^-$, $HS^-$, and $H_2PO_4^-$). These ions can both donate a proton (behaving as an acid, $K_{a2}$) and accept a proton from water (hydrolysis, controlled by $K_{a1}$). Their pH is approximated as the average of the two $pK_a$ values. $CH_3COONH_4$ is a WA-WB salt; its pH is also independent of concentration, but its formula is $7 + \frac{1}{2}(pK_a - pK_b)$.