A buffer was made by mixing 0.1886 moles of CH3CH2CO2H with 0.1517 moles of KCH3CH2CO2 and diluting to exactly 1 liter. What will be the pH after addition of 10.00 mL of 0.2441 M HBr to 50.00 mL of the buffer? Ka(CH3CH2CO2H) = 1.300e-5
A buffer was made by mixing 0.1886 moles of CH3CH2CO2H with 0.1517 moles of KCH3CH2CO2 and diluting to exactly 1 liter. What will be the pH after addition of 10.00 mL of 0.2441 M HBr to 50.00 mL of the buffer? Ka(CH3CH2CO2H) = 1.300e-5. Note: only a portion of the original buffer is used in the second part of the problem.
Key Concept: Buffers resist pH change and are prepared by mixing the conjugate acid and base together. Addition of either a strong acid or a strong base will cause a small shift in pH to a lower or higher pH, respectively.
Strategy: Determine the moles of HA and A− the buffer prior to addition of either a strong acid or base by multiplying by the molarity and volume (50 mL) → determine mole of strong acidadded to the buffer. Adjust the moles to account for loss of conjugate base and formation of conjugate acid with addition of a strong acid or loss of conjugate acid and formation of conjugate base with addition of a strong base → use Henderson-Hasselbach equation to find the pH.
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