Question

1a) The concentrations of acid and conjugate base in a buffer are determined experimentally to be 0.062 M and 0.032 M, respectively. If the total buffer concentration given on the bottle (the true value) is 0.052 M, then what is the percent error of the experimental value?

b) A buffer solution is titrated with 0.027 M HCl solution. The initial volume of the buffer is 25.00 mL. The equivalence point of the titration is determined to be 4.47 mL. What is the concentration of conjugate base (in M) in the buffer solution? Assume the stoichiometry of acid to base is 1:1.

Answer 1

1a) The concentrations of acid and conjugate base in a buffer are determined experimentally to be 0.062 M and 0.032 M, respectively. If the total buffer concentration given on the bottle (the true value) is 0.052 M, then what is the percent error of the experimental value?

Solution :-

Experimental total concentration of the buffer = 0.062 M +0.032 M = 0.094 M

True value of the buffer concentration = 0.052 M

% error = [(experimental value – true value)/true value]*100%

             = [(0.094-0.052)/0.052] * 100 %

            = 80.8 %

b) A buffer solution is titrated with 0.027 M HCl solution. The initial volume of the buffer is 25.00 mL. The equivalence point of the titration is determined to be 4.47 mL. What is the concentration of conjugate base (in M) in the buffer solution? Assume the stoichiometry of acid to base is 1:1.

Solution :-

Using the molarity and volume of the   HCl needed to reach the equivalence point we can find the concentration of the conjugate base in the buffer

Moles of HCl = molarity x volume in liter

                        = 0.027 mol per L * 0.00447 L

                        = 0.000121 mol HCl

Stoichiometry of the base and HCl is 1 :1 therefore moles of base are same as moles of HCl

Hence moles of base are 0.000121 mol

Molarity of base = moles / volume

                              = 0.000121 mol / 0.025 L

                              = 0.00483 M

Therefore the molarity of the conjugate base in the buffer was 0.00483 M