Question

Determine the mass (ing) of sodium butanoate (NaC3H7COO) that must be added to 31.4 mL of 0.888 M butanoic acid to yield a pH of 5.73. Report your answer to 3 significant figures.

Calculate the buffer ratio (base/acid) required for a buffer of pH = 2.93 that is prepared by mixing benzoic acid and sodium benzoate. A table of pKa values can be found here. Report your answer to 2 significant figures in scientific notation.

Answer 1

pH = pka + log [ conjugate base] / [ acid]

where acid is HC3H7CO2 , ist conjugate base is NaC3H7CO2

5.73 = 4.745 + log ( [NaC3H7CO2] / 0.888)

[NaC3H7CO2] = 8.6

NaC3H7CO2 moles = M x V (inL) = 8.6 x 0.0314 = 0.26937

Mass of NaC3H7CO2 = moles x molar mass of NaC3H7CO2 = 0.26937 mol x 110 g/mol = 29.6g

2) using Henderon eq , we calculate the ratio , pka of benzoic acid is 4.2

hence 2.93 = 4.2 + log [ conjugate base] /[acid]

[conjugate base] /[acid] = 10^( 2.93-4.2) = 0.054