Problem: Consider a solution consisting of the following two buffer systems: H2CO3    ⇌ HCO3 - + H +          pKa = 6.4 H2PO4 -   ⇌ HPO4-2 + H +         pKa = 7.2 At pH 6.4, which one of the following is TRUE of the relative amounts of acid and conjugate base present? A) [H2CO3] = [HCO3 - ] and [H2PO4 - ] > [HPO4 -2 ] B) [H2CO3] > [HCO3 - ] and [H2PO4 - ] > [HPO4 -2 ] C) [H2CO3] = [HCO3 - ] and [HPO4 -2 ] > [H2PO4 - ] D) [HCO3 - ] > [H2CO3] and [HPO4 -2 ] > [H2PO4 - ]  E) [H2CO3] > [HCO3 - ] and [HPO4 -2] > [H2PO4 -]

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Problem Details

Consider a solution consisting of the following two buffer systems:

H2CO3    ⇌ HCO3 - + H +          pKa = 6.4

H2PO4 -   ⇌ HPO4-2 + H +         pKa = 7.2

At pH 6.4, which one of the following is TRUE of the relative amounts of acid and conjugate base present?

A) [H2CO3] = [HCO3 - ] and [H2PO4 - ] > [HPO4 -2 ]

B) [H2CO3] > [HCO3 - ] and [H2PO4 - ] > [HPO4 -2 ]

C) [H2CO3] = [HCO3 ] and [HPO4 -2 ] > [H2PO4 ]

D) [HCO3 ] > [H2CO3] and [HPO4 -2 ] > [H2PO4

E) [H2CO3] > [HCO3 - ] and [HPO4 -2] > [H2PO4 -]

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