Question

1. A solution is made by mixing 50mL of 2.0M K2HPO4 and 25mL of 2.0M KH2PO4. The solution is diluted to a final volume of 200mL. what is the pH of the final solution

Answer 1

Answer:

The pH of the final solution is 7.15

Explanation:

50 mL of 2.0 M of $K_2HPO_4$ and 25 mL of 2.0 M of $KH_2PO_4$ were mixed to make a solution

Final volume of the solution after dilution = 200 mL

Final concentration of $K_2HPO_4, [K_2HPO_4] = \frac{50 mL\times 2 M}{200 mL} = 0.5 M$

Final concentration of$KH_2PO_4, [KH_2PO_4] = \frac{25 mL\times 2 M}{200 mL} = 0.25 M$

We use Hasselbach- Henderson equation:

$pH = pK_a+ log \frac{[salt]}{[acid]}pka of KH_2PO_4 = 6.85$

Substituting the values:

$pH = 6.85+ log \frac{0.5}{0.25}pH = 6.85+ log 2pH = 6.85+ 0.3 = 7.15$

Therfore,  the pH of the final solution is 7.15