If 50. 0 g of formic acid (HCHO2, ka = 1. 8 x 10^-4) and 30. 0 g of sodium formate (NaCHO2) are dissolved to make 500 ml. of solution, then the pH of this solution is 3.358.
Option C is correct option.
Given,
Given mass of formic acid = 50 g
Given mass of sodium formate = 30 g
Volume of formic acid = 500 ml
Volume of sodium formate = 500 ml
Molar mass of formic acid = 46 g
Molar mass of sodium formate = 68 g
<h3 /><h3>Calculation of concentration of formic acid and sodium formate</h3>
Molar concentration is defined as the ratio of number of moles and the volume of solution.
Concentration of formic acid
Ca = 50/(46×500)
= 0.00217 m
Concentration of sodium formate
Cb = 30/(68×500)
= 0.00088 m
Using Henderson Hesselbalch equation,
pH = pKa + log(Cb/Ca)
pKa = -log(1.8 × 10^(-4))
= 3.75
Substituting the value of pKa we get,
pH = 3.75 + log(0.00088/0.00217)
pH = 3.75-0.392
pH = 3.35
Thus the value of pH of solution containing formic acid and sodium formate is 3.35.
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