5. If a buffer solution of acetic acid - acetate ion (pH=4.74) had equal moles of HCN and $CN-$ added to it, what would the pH of the resulting solution be? (pK$$_a of HCN=9.21)

a) pH = 4.74
b) pH = 9.21
c) pH cannot be determined
d) 4.74 < pH < 9.21

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