First slide

Basic Buffer

Question

At 298 K, the p^H of mixture containing 1000 ml of 0.1 M H₂SO₄ and 500 ml of 1.2 M NH₄OH is (p^k_^b of NH₄OH = 4.77)

Moderate

A

8.929
B

9.23
C

9.531
D

4.469

Solution

$\begin{array}{l} V_{a} N_{a} = 1000 (0 .1) 2 = 200 meq \\ V_{b} N_{b} = 500 (1 .2) = 600 meq \\ \underset{}{SA + WB} \to salt + water \\ 200 meq 200 meq 200 meq \\ Left over WB = (600 - 200) meq = 400 meq; \end{array}$
This mixture contains WB and its salt of strong acid.
This mixture acts like a basic buffer.
$\begin{array}{l} ∴ p^{OH} = p^{K_{b}} + \log \frac{V_{S} N_{S}}{V_{a} N_{a}} \\ p^{OH} = 4 .77 + \log \frac{200}{400} \\ p^{OH} = 4 .77 - 0 .301 \\ p^{H} = 14 - 4 .77 + 0 .301 \\ p^{H} = 9 .531 \end{array}$

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