Q38 / 160 · TS EAMCET 2004 · Chemistry

Study the following table: \begin{array}{c|c|c} \hline \begin{array}{c}\text { Buffer } \\ \text { Solution }\end{array} & \begin{array}{c}\text { Volume (in } \mathrm{mL} \text { ) of } \\ \text { 0.M Weak acid }\end{array} & \begin{array}{c}\text { Volume (in } \mathrm{mL} \text { ) of } \\ 0.1 \mathrm{M} \text { sodium salt of } \\ \text { weak acid }\end{array} \\ \hline I. & 4.0 & 4.0 \\ II. & 4.0 & 40.0 \\ III. & 40.0 & 4.0 \\ IV. & 0.1 & 10.0 \\ \hline \end{array} Which of the two sets of butter solutions have least $\mathrm{pH}$ ?

  • A
    I and II
  • Correct answer
    B
    I and III
  • C
    II and III
  • D
    II and IV

Solution

For a buffer solution, $\mathrm{pH}$ is given by Henderson, equation, $$ \mathrm{pH}=\mathrm{pKa}+\log \frac{[\text { salt }]}{[\text { acid }]} $$ Hence, $\mathrm{pH}$ is least when concentration of acid is higher than that of salt.

Hence, the correct answer is option: 'B'.

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