Answer
$pH \approx 2.938$
Work Step by Step
1. Calculate the concentration values:
Furoic Acid:
$C_1*V_1 = C_2*V_2$
$0.25*0.030 = C_2*0.125 $
$C_2 = \frac{0.0075}{0.125}$
$C_2 = 0.06M$
Sodium Furoate:
$C_1*V_1 = C_2*V_2$
$0.22*0.020 = C_2 * 0.125$
$C_2 = \frac{0.0044}{0.125}$
$C_2 = 0.0352M$
2. Use the Henderson-Hassebalch's formula to find the pH:
$pH = pKa + log(\frac{[Salt]}{[Acid]})$
*As we calculated in 17.85a, the pKa value is 3.170;
$pH = 3.170 + log(\frac{0.0352}{0.06})$
$pH \approx 3.170 + (-0.232)$
$pH \approx 2.938$
