Question

Aqueous solutions of phosphoric acid and sodium nitrite are combined, and the following equilibrium is established. H3PO4(aq) + NO2-(aq) H2PO4-(aq) + HNO2(aq) The equilibrium constant Kc for this reaction is greater than one. Based on this information, which of the following statements is correct?

a) Phosphoric acid is a weaker acid than nitrous acid.

b) Nitrous acid is a weaker acid than water.

c) The nitrite anion is a weaker base than the dihydrogen phosphate anion.

d) The dihydrogen phosphate anion is a stronger acid than nitrous acid.

e) Phosphoric acid is a stronger acid than nitrous acid.

I think the correct answer is E. Can anyone confirm?

Answer 1

The expression for K_c = [product]/[reactant]

Since the equilibrium constant is greater than 1, the favored towards the products.

Remember that the equilibrium favors reaction of the strong aid and strong base and formation of the weak acid and weak base.

So, phosphoric acid is strong acid and nitrate is strong base.

Dihydrogen phosphate is weak base and nitrous acid is a weak acid.

So, the following statements are correct:

e) Phosphoric acid is a stronger acid than nitrous acid.