A buffer consists of a weak acid or base, and the salt of that acid or base. Con
ID: 918948 • Letter: A
Question
A buffer consists of a weak acid or base, and the salt of that acid or base. Consider a buffer made by combining the weak acid HA with its salt, A: HA(aq)+H2O(l)A(aq)+H3O+(aq) Ka=[A][H3O+][HA] The H3O+ concentration of this buffer can be calculated using the Ka expression: [H3O+]=Ka[HA][A] You can use this expression when solving for pH, or you can simplify the expression even more. Taking the negative log of this expression, you have log[H3O+]=log[Ka]log[HA][A] Since log[H3O+]=pH and log[Ka]=pKa, this can be further simplified to pH=pKa+log[A][HA]
A lactic acid/lactate ion buffer solution contains 0.32 M HC3H5O3 and 0.86 M C3H5O3, respectively. The Ka value of lactic acid is 1.4×104. Calculate the pH of this buffer.
Express the pH numerically.
Explanation / Answer
pH = pka log(C3H5O3/HC3H5O3)
pka = -log ka = -log(1.4*10^(-4)) = 3.85
pH = 3.85+log(0.86/0.32)
= 4.28
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.