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Correct Answer: C
Correct Answer: C
Method / Topic: General Chemistry
The correct option matches the required rule and the given information.
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Correct Answer: C
Method / Topic: General Chemistry
Added H+ reacts with acetate: A− + H+ → HA. Acetate decreases from 0.100 to 0.090 mol, while acetic acid increases from 0.100 to 0.110 mol. Then pH = 4.76 + log(0.090/0.110) = 4.76 + log(0.818) ≈ 4.76 − 0.087 = 4.67. The buffer limits the pH decrease. This result follows from the balanced chemical relationship and the stated conditions; no unstated biological assumption is needed. On MCAT chemistry problems, first identify the governing principle, write the relevant equation with units, and only then substitute values. Check whether the
prevents dosage, dilution, and preparation errors.
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PASSAGE 3 — ACETATE BUFFER A researcher prepares 1.00 L of a buffer containing 0.100 mol CH3COOH and 0.100 mol CH3COO−. The acid dissociation constant of acetic acid is Ka = 1.8 × 10−5, so pKa ≈ 4.76. Volume changes after small additions may be neglected. The Henderson–Hasselbalch equation is pH = pKa + log([A−]/[HA]). QUESTION 7: What is the approximate pH after 0.010 mol HCl is added to the buffer?
Explanation
Correct Answer: C
Method / Topic: General Chemistry
The correct option matches the required rule and the given information.
Short Explanation
Detailed Explanation
Correct Answer: C
Method / Topic: General Chemistry
Added H+ reacts with acetate: A− + H+ → HA. Acetate decreases from 0.100 to 0.090 mol, while acetic acid increases from 0.100 to 0.110 mol. Then pH = 4.76 + log(0.090/0.110) = 4.76 + log(0.818) ≈ 4.76 − 0.087 = 4.67. The buffer limits the pH decrease. This result follows from the balanced chemical relationship and the stated conditions; no unstated biological assumption is needed. On MCAT chemistry problems, first identify the governing principle, write the relevant equation with units, and only then substitute values. Check whether the
prevents dosage, dilution, and preparation errors.
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