| Direction: Solution of an acid and its anion (that is its conjugate base) or of a base and its common cation is buffer. On adding small amount of acid or base, the pH of solution changes very little (negligible change). The pH of buffer solution is determined as follows: |
| ph of acidic in buffer \[=\,p{{K}_{a}}+\,\log \,\,\frac{[conjugate\,base]}{[acid]}\] |
| \[pOH\] of basic buffer \[=p{{K}_{b}}+\log \,\frac{[conjugate\,\,acid]}{[base]}\] |
| A buffer solution can work effectively provided the value of \[\frac{[conjugate\,\,base]}{[acid]}\] for acidic buffer or \[\frac{[conjugate\,\,acid]}{[acid]}\] for basic buffer lies within the range of 1 : 10 or 10 : 1. |
A) 5.40
B) 5.88
C) 4.92
D) None of these
Correct Answer: B
Solution :
\[BOH+HCl\,\,\,BCl+{{H}_{2}}O\] At equl. point \[{{N}_{1}}{{V}_{1}}={{N}_{2}}{{V}_{1}}\] \[[BCl]=\frac{20\times 0.08}{20+20}=0.04\] \[pH=7-\frac{1}{2}p{{K}_{b}}-\frac{1}{2}\,\log \,C\] \[\therefore \] \[p{{K}_{b}}=5.4\] \[{{B}^{+}}+O{{H}^{-}}\xrightarrow{\,}\,BOH,\] Intial 1.6 0.4 Final 1.2 _ 0.4 moles Basic buffer is formed. \[pOH=p{{K}_{b}}+\log \,\frac{[{{B}^{+}}]}{[BOH]}\] \[=5.4+\log \,\left( \frac{1.2}{0.4} \right)\] \[pOH=5.88\]
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