t Calculating the pH of an Acid Buffer A buffer consists of a weak acid or base,
ID: 874362 • Letter: T
Question
t Calculating the pH of an Acid Buffer 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) H20 (l) A (aq) +H30+ (aq) A 1H30 Ka DHA] The H3O+ concentration of this buffer can be calculated using the Ka expression: KalHA LA 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 DHA] log H3O+] log Ka -log Since -loglH3 pH and -log Kal pKa this can be further simplified to LA 1 pH pKa log DHA] Part A A lactic acid/lactate ion buffer solution contains 0.40MHC3H5O3 and 0.90MC3H5O3 respectively. The Ka value of lactic acid is 1.4 x 10 Calculate the pH of this buffer. Express the pH numerically. pH Submit Hints My Answers Give Up Review Part Provide Feedback ContinueExplanation / Answer
Ka = 1.4 x 10^-4
pKa = -log(1.4 x 10^-4)
= 3.85
For acidic buffer
Henderson-Hasselbalch equation
pH = pKa + log[salt/acid]
pH = pKa + log[lactate/lactic acid]
pH = 3.85+ log[0.90/0.40]
= 4.20
pH of buffer = 4.20
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