A laboratory technician must choose a phosphate buffer that most effectively resists…

CHEMISTRY · Single correct · A Level · Chemistry · Acids and bases · Acids and bases

Problem

A laboratory technician must choose a phosphate buffer that most effectively resists a sudden addition of strong acid. Each 0.20 L solution below contains a total of 0.40 M buffer components (H2_2PO4−_4^{−} + HPO42−_4^{2−}). Which choice provides the greatest protection against the acid? (a) [H2PO4−]=0.15 M;  [HPO42−]=0.25 M[\mathrm{H_2PO_4^-}] = 0.15\,\text{M};\;[\mathrm{HPO_4^{2-}}] = 0.25\,\text{M} (b) [H2PO4−]=0.20 M;  [HPO42−]=0.20 M[\mathrm{H_2PO_4^-}] = 0.20\,\text{M};\;[\mathrm{HPO_4^{2-}}] = 0.20\,\text{M} (c) [H2PO4−]=0.25 M;  [HPO42−]=0.15 M[\mathrm{H_2PO_4^-}] = 0.25\,\text{M};\;[\mathrm{HPO_4^{2-}}] = 0.15\,\text{M} (d) [H2PO4−]=0.10 M;  [HPO42−]=0.30 M[\mathrm{H_2PO_4^-}] = 0.10\,\text{M};\;[\mathrm{HPO_4^{2-}}] = 0.30\,\text{M}

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