What volume of 0.10 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 ? pK_(a) for formic acid is 3.80 .

What volume of 0.10 M sodium formate solution should be added to 50 ml

1.	What volume of 0.10 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 ? pK_(a) for formic acid is 3.80 .
Answer» Solution :`pH=pK_(a) + log.(["SALT"])/(["Acid"]) :. 4=3.8+log.(["Salt"])/(["Acid"]) ORLOG.(["Salt"])/(["Acid"]) = 0.2 or(["Salt"])/(["Acid"])=1.5849` or `("No. of moles of salt")/("No. of moles of acid")=1.5849`(`:'` Volume is same for both) No. of moles of acid PRESENT `=(0.05)/(1000)xx50=2.5xx10^(-3)` `:.` No. of moles of salt `=1.5849 xx 2.5xx10^(-3)=3.962xx10^(-3)` Hence, volume of 0.1 M sodiumformate required `=(1000)/(0.1) xx 3.962xx10^(-3)=39.62 ml`