First slide

Acidic buffer

Question

20 ml of 0.1 M acetic acid is mixed with 50ml of potassium acetate. K_a of acetic acid = 1.8 × 10^–5 at 27⁰C. The concentration of potassium acetate if pH of the mixture is 4.8

Moderate

A

0.1M
B

0.04M
C

0.4M
D

0.02M

Solution

$\large {P^H} = {P^{Ka}} + \log \frac{{\left[ {Salt} \right]}}{{\left[ {Acid} \right]}}\$
$\large \Rightarrow 4.8 = 4.74 + \log \left( {\frac{{N \times 50}}{{0.1 \times 20}}} \right)\$
$\large Assuming4.74 \sim 4.8\$
$\large \log \left( {\frac{{N \times 50}}{{0.1 \times 20}}} \right) = 0$
$\large N \times 50 = 0.1 \times 20$
$\large N = \frac{2}{{50}}$
$\large N = 0.04M$

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