Sodium carbonate (kc = 3.67 *10^-3) is a weak base that can react with two moles of water according to the following equilibrium:


Na2Co3 (aq) + 2 H2O yields H2CO3 + 2 NaOH

if 8.14 mMol of sodium carbonate is dissolved in 100ml of water and allowed to reach equilibrium, what will the concentration of its conjugate acid (H2CO3) be?

1 answer

8.14 mmol/0.100L = 81.4 mM = 0.0814M
.........Na2SO3 + 2H2O ==> H2CO3 + 2NaOH
initial 0.0814M...............0.......0
change...-x..................x........x
equil...0.814-x..............x........x

Substitute into the Kc expression and solve for x.