What will be the effect of adding 0.5 mL of 0.1 M HCl to 100 mL of a phosphate buffer in which [H₂PO₄^-] = [HPO₄^2-] = 0.35 M? A) The pH will increase slightly. B) The pH will increase significantly. C) The pH will decrease slightly. D) The pH will decrease significantly. E) Since it is a buffer solution, the pH will not be affected.

Question

Quizplus · Accepted Answer

HCl is an acid, so it will react with the base in the buffer, which is HPO42-. The equation for this reaction is:
HPO42- + H+ -> H2PO4-
This reaction consumes H+, which will cause the pH to increase. However, the increase will be slight because the buffer system will resist the change in pH due to the presence of both the acid and its conjugate base. Therefore, the correct answer is (C) the pH will decrease slightly.

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