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1 M benzoic acid `(pK_a=4.20)` and 1 M `C_6H_5COONa` solutions are given separately What is the volume of benzoic acid required to prepare a 300 ml buffer solution of pH =4.5 ? [log 2 =0.3]A. `200 ml`B. `150ml`C. `100ml`D. `50ml` |
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Answer» Correct Answer - C `pH=pK_(a)+log``(["Salt"])/([Acid])` `:. 4.5=4.2+log``(["Salt"])/([Acid])=log``(["Salt"])/([Acid])=0.3` (since `log 2=0.3`) `:. (["Salt"])/([Acid])=2` Let `Vml 1 M C_(6)H_(5)COOH` solution and `(300-V) 1 M C_(6)H_(5)COONa` solution be mixed together `[Acid]=(Vxx1)/(1000)xx(1000)/(300)` , `[Salt]=(300-V)/(1000)xx(1000)/(300)` `[Acid]=(V)/(300)`, `["Salt"]=(300-V)/(300)` `:. (300-V//300)/(V//300)=2=300-V=2V :. V=100 ml` |
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