Question

If 50 ml of 0.2 M KOH is added to 40 ml of 0.5 M HCOOH. the pH of the resulting solution is: (Ka = 1.8 × 10–4, log 18 = 1.26)

• A. 3.74
• B. 5.64
• C. 7.57
• D. 3.42

Answer 1

Answer: (A)

3.74

Answer 2

HCOOH + KOH $\longrightarrow$HCOOK + H2O

milimole 20 10

10 – 10

pH = pKa + log $\frac{\lbrack HCOO^{-}\rbrack}{\lbrack HCOOH\rbrack}$ = 3.74 + log $\left( \frac{10}{10} \right)$

$\Rightarrow$ pH = 3.74