First slide

Acidic buffer

Question

Find the change in pH when 0.01 mole CH₃COONa is added to one litre of 0.01M CH₃COOH solution (pKa = 4.74 )

Easy

A

3.27
B

4.74
C

1.37
D

2.74

Solution

P^H of a 0.01 M CH₃CHOOH solution $= \frac{1}{2}\left[ {{P^{{K_a}}} - \log C} \right]$
P^H of a 0.01 M CH₃CHOOH solution $= \frac{1}{2}\left[ {4.74 + 2} \right]$
P^H of a 0.01 M CH₃CHOOH solution = 3.37
P^H of an acidic buffer $= {P^{{K_a}}} + \log \frac{{\left[ {salt} \right]}}{{\left[ {acid} \right]}}$
P^H of an acidic buffer $= {P^{{K_a}}} + \log \frac{{\left[ {salt} \right]}}{{\left[ {acid} \right]}}$
                                        $= 4.74 + \log \frac{{0.01}}{{0.01}}$
                                        $= 4.74$
Thus, change in P^H = 4.74 - 3.37 = 1.37

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