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  • What volume of 0.1 M sodium formate solution should be added to 50 ml of 0.05 M formic acid to produce a buffer solution of pH = 4.0; pKa of formic acid is 3.80?<div class='qna-

What volume of 0.1 M sodium formate solution should be added to 50 ml of 0.05 M formic acid to produce a buffer solution of pH = 4.0; pKa of formic acid is 3.80?

Option: 1

39.62 mL


Option: 2

39.62 L


Option: 3

396.2 mL


Option: 4

396.3 L


Answers (1)

best_answer

\begin{array}{l}{\text { Suppose, } \mathrm{V} \mathrm{ml} \text { of } 0.1 \mathrm{M} \text { HCOONa is }}{\text {mixed to } 50 \mathrm{ml} \text { of } 0.05 \mathrm{\: M\: HCOOH}}\end{array}

\begin{array}{l}{\text { [Molarity ] = } \frac{\text { Total millimole }}{\text { Total volume }}} \\\\ {\text { In mixture }[\mathrm{HCOONa}]=\frac{0.1 \times \mathrm{V}}{(\mathrm{V}+50)}} \\\\ {[\mathrm{HCOOH}]=\frac{50 \times 0.05}{\mathrm{V}+50}}\\\\\mathrm{pH}=-\log \mathrm{Ka}+\log \frac{[\mathrm{Salt}]}{[\mathrm{Acid}]} \\\\ {\text { 4.0 }=3.80+\log _{10} \frac{(0.1 \times \mathrm{V})}{(\mathrm{V}+50) / 2.5 /(\mathrm{V}+50)}} \\\\ {\mathrm{V}=39.62 \mathrm{ml}}\end{array}

Therefore, option(1) is correct

Posted by

Ritika Harsh

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