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Question: Which of the following acid/base pairs yields the most nearly neutral aqueous solution when mixed?

a) HCl/NaF

 b) H2CO3/2 NaOH

c) HCl/NaOH

d) HBr/NH3

Explanation:

a) incorrect, strong acid + weak base forms NaCl and HF, the HF hydrolyzes to H3O+ and F-, pH<7

b) incorrect, weak acid + strong base forms Na2CO3 + 2 H2O, and the CO32- ion autoionizes water, to create OH-  ions, pH>7

c) correct, strong acid + strong base forms NaCl + H2O and salt ions do not react with water to change pH, pH=7

d) incorrect, strong acid + weak base forms NH4Br, the NH4+ ions weakly dissociates to NH3 + H+ and Br- does not react with water, pH<7

Topics #Acid-base pairs #mcat #mcat questions #practice mcat questions