Question

A lactic acid/lactate ion buffer solution contains 0.42 m hc3h5o3 and 0.60 m c3h5o3−, respectively. the ka value of lactic acid is 1.4×10−4. calculate the ph of this buffer.

Answer 1

Answer is: the Ph of this buffer is 4.
c(lactic acid - C₃H₆O₃) = 0.42 M.
c(C₃H₅O₃⁻) = 0.60 M.
Ka(C₃H₆O₃) = 1.4·10⁻⁴.
pKa = -logKa = 3.85.
Henderson–Hasselbalch equation: pH = pKa + log(c(C₃H₅O₃⁻)/c(C₃H₆O₃)).
pH = 3.85 + log(0.60 M/0.42 M).
pH = 3.85 + 0.15.
pH = 4.00.