Question

Given the system at equilibrium:

H3PO4 + 3 H2O <-----> 3 H3O+ + PO4^3-
If Na3PO4(s) is added, there will be a decrease in the
concentration of

A) Na+
B) PO4^3–
C) H3O+
D) H2O

Answer 1

Adding Na3PO4(s) will introduce more PO4^3- ions into the solution, which will react with H3O+ ions to form more H3PO4 and H2O through the reverse reaction. This will shift the equilibrium to the left, decreasing the concentration of H3O+ ions and increasing the concentration of H3PO4 and H2O. Therefore, the concentration of H3O+ ions will decrease, and the correct answer is (C) H3O+.