An industrial fermentation produces lactic acid steadily at a rate that releases the…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
An industrial fermentation produces lactic acid steadily at a rate that releases the equivalent of 0.010 mol H⁺ per liter per hour. To keep the culture near pH 5.0, engineers consider the three citrate buffer systems listed below, each initially at 1.00 L and 25 °C. All buffers have the same total concentration of citrate species (0.50 M) but different component ratios.
Buffer X: 0.40 M H₂Cit⁻ and 0.10 M HCit²⁻ (pKₐ₂ = 4.77)
Buffer Y: 0.25 M H₂Cit⁻ and 0.25 M HCit²⁻
Buffer Z: 0.10 M H₂Cit⁻ and 0.40 M HCit²⁻
(a) Calculate the initial pH of each buffer.
(b) For each buffer, calculate the maximum number of hours the culture can run before its pH falls below 4.80, assuming no external pH control other than the buffer and negligible volume change.
(c) Based on your calculations, recommend which buffer the engineers should choose. Justify your recommendation quantitatively and qualitatively.
(d) Propose one practical modification to your chosen buffer system (other than changing temperature) that would extend the allowable operating time, and explain the chemical principles behind your proposal.