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NEET 2011
Exam
NEET
Year
2011
Subject
Chemistry
Chapter
Ionic Equilibrium

NEET 2011 · Chemistry · Ionic Equilibrium

A buffer solution is prepared in which the concentration of NH_3 is...

A buffer solution is prepared in which the concentration of NH3\mathrm{NH}_3 is 0.30M0.30 \mathrm{M} and the concentration of NH4+\mathrm{NH}_4^{+}is 0.20M0.20 \mathrm{M}. If the equilibrium constant, KbK_b for NH3\mathrm{NH}_3 equals 1.8×10−51.8 \times 10^{-5}, what is the pH\mathrm{pH} of this solution? (log⁡2.7=0.43)(\log 2.7=0.43)

Options

  1. A9.43
  2. B11.72
  3. C8.73
  4. D9.08

Correct answer

A. 9.43

Step-by-step solution

pOH=pKb+log⁡[ Salt ][ Base ]=−log⁡Kb+log⁡[ Salt ][ Base ]=−log⁡1.8×10−5+log⁡0.200.30=5−0.25+(−0.176)=4.75−0.176=4.57∴pH=14−4.57=9.43\begin{aligned}\mathrm{pOH}& =\mathrm{p}K_{\mathrm{b}}+\log\frac{[\text{ Salt }]}{[\text{ Base }]}\\ & =-\log K_{\mathrm{b} }+\log\frac{[\text{ Salt }]}{[\text{ Base }]}\\ & =-\log 1 .8 \times10^{-5}+\log \frac{0.20}{0.30}\\ & =5-0.25+(-0.176) \\ & =4.75-0.176=4.57 \\ \therefore \mathrm{pH}& =14-4.57=9.43 \end{aligned}
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