Equilibrium Question 395
A buffer solution with $ pH $ 9 is to be prepared by mixing $ NH_4Cl $ and $ NH_3 $. Calculate the number of moles of $ NH_4Cl $ that should be added to one litre of $ 1.0,M\ NH_3., $
$ [K_{b}=1.8\times {10^{-5}}] $ [UPSEAT 2001]
Options:
3.4
2.6
1.5
1.8
Show Answer
Answer:
Correct Answer: D
Solution:
$ pH=-logK_{b}+log\frac{[\text{ Base }]}{[\text{ Acid }]} $
$ pH=-log,[1.8\times {10^{-5}}]+log\frac{[\text{ Salt }]}{1\text{.0}} $
$ 9=4.7+\log \frac{[\text{ Salt }]}{1.0} $ ; $ \log \frac{[\text{ Salt }]}{1.0}=9-4.7=4.3 $
$ \frac{[\text{ Salt }]}{1.0}=Antilog\frac{1}{4.3};[S\text{alt }]=1.8 $
BETA
