An aqueous solution of ammonium nitrate,

CHEMISTRY · Multi-part · AP · Chemistry · Acids and Bases · Acids and Bases

Problem

0.20\,\text{M}

aqueous solution of ammonium nitrate,

\mathrm{NH_4NO_3}

, is prepared at

25\;^{\circ}\text{C}

. The base-dissociation constant of ammonia is

K_b(\mathrm{NH_3})=1.8\times10^{-5}

. Parts (a) Write the principal proton-transfer equilibrium that occurs when the

\mathrm{NH_4^+}

ion is present in water. (b) Set up a concentration-based ICE (Initial–Change–Equilibrium) table for the reaction written in part (a) and define the equilibrium expression for the associated acid-dissociation constant

K_a

\mathrm{NH_4^+}

in terms of equilibrium concentrations. (c) Calculate

K_a(\mathrm{NH_4^+})

by using the relationship between

K_a

K_b

, and

K_w

for a conjugate acid–base pair. (d) Use your ICE table and the value of

K_a

from part (c) to determine the equilibrium hydronium-ion concentration and the pH of the

0.20\,\text{M}

\mathrm{NH_4NO_3}

solution. Report the pH to two decimal places. (e) Indicate whether water acts as an acid or as a base in the equilibrium you analyzed and support your answer with evidence from your calculations.

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