Silver chromate, Ag2CrO4(s), is characterized by a very small solubility‐product constant, Ksp=1.1×10−12 at 25 °C. In an industrial quality‐control test, a solution that is 0.025 M in Na2CrO4 is used as the medium into which a small amount of solid Ag2CrO4 is introduced.
Use the information provided to answer the questions below. Show all work, include units, and explain the validity of any approximations employed.
(a) Write the dissolution equilibrium for Ag2CrO4 and express Ksp in terms of the molar solubility s when the salt dissolves in a solution that already contains chromate ion.
(b) A student first assumes that the change in chromate ion concentration upon dissolution is negligible compared with 0.025 M. Use this assumption to obtain an approximate value for s, and then calculate the percent error introduced by the assumption using the exact expression derived in part (a).
(c) Without making the approximation used in part (b), solve exactly for the molar solubility of Ag2CrO4 in the 0.025 M Na2CrO4 solution at 25 °C.
(d) Determine the equilibrium concentration of Ag+ in the solution, and comment on how the common‐ion effect has altered that concentration relative to its value in pure water.