Dihydrogen phosphate ion can transfer a proton to ammonia in water

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

Problem

Dihydrogen phosphate ion H2PO4−\mathrm{H_2PO_4^-} can transfer a proton to ammonia in water. Which choice gives both the correct balanced net ionic equation and the correct identification of the resulting conjugate acid–base pairs? (a) Equation: H2PO4−(aq)+NH3(aq)⇌HPO42−(aq)+NH4+(aq)\mathrm{H_2PO_4^-(aq) + NH_3(aq) \rightleftharpoons HPO_4^{2-}(aq) + NH_4^+(aq)}; Conjugate pairs: H2PO4−/NH4+\mathrm{H_2PO_4^- / NH_4^+} and NH3/HPO42−\mathrm{NH_3 / HPO_4^{2-}} (b) Equation: H2PO4−(aq)+NH3(aq)⇌PO43−(aq)+NH4+(aq)\mathrm{H_2PO_4^-(aq) + NH_3(aq) \rightleftharpoons PO_4^{3-}(aq) + NH_4^+(aq)}; Conjugate pairs: H2PO4−/PO43−\mathrm{H_2PO_4^- / PO_4^{3-}} and NH3/NH4+\mathrm{NH_3 / NH_4^+} (c) Equation: H2PO4−(aq)+NH3(aq)⇌HPO42−(aq)+NH4+(aq)\mathrm{H_2PO_4^-(aq) + NH_3(aq) \rightleftharpoons HPO_4^{2-}(aq) + NH_4^+(aq)}; Conjugate pairs: H2PO4−/HPO42−\mathrm{H_2PO_4^- / HPO_4^{2-}} and NH3/NH4+\mathrm{NH_3 / NH_4^+} (d) Equation: H2PO4−(aq)+NH3(aq)⇌HPO42−(aq)+NH4+(aq)+H2O(l)\mathrm{H_2PO_4^-(aq) + NH_3(aq) \rightleftharpoons HPO_4^{2-}(aq) + NH_4^+(aq) + H_2O(l)}; Conjugate pairs: H2PO4−/HPO42−\mathrm{H_2PO_4^- / HPO_4^{2-}} and NH3/NH4+\mathrm{NH_3 / NH_4^+}

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