The saturated CuSO 4(aq) shown above is leftuncovered on a lab bench at a constanttemperature. As the solution evaporates, 1.0 mLsamples of the solution are removed every threedays and the [SO42] in the samples is measured.It is observed that the [SO 42] in the solution didnot change over time. Which of the following besthelps to explain the observation?(A) As the solution evaporates, Cu 2+(aq) andSO42(aq) leave the beaker along with thewater molecules.(B) As the solution evaporates, the dissolution ofCuSO4(s) in the beaker decreases.(C) The evaporation of water is endothermic, somore CuSO4(s) dissolves exothermically inthe solution, which increases the [SO42].(D) As water evaporates, more CuSO 4(s)precipitates out of the solution in the beaker.Unauthorized copying or reuse ofany part of this page is illegal. GO ON TO THE NEXT PAGE.-17-
Question
The saturated CuSO 4(aq) shown above is leftuncovered on a lab bench at a constanttemperature. As the solution evaporates, 1.0 mLsamples of the solution are removed every threedays and the [SO42] in the samples is measured.It is observed that the [SO 42] in the solution didnot change over time. Which of the following besthelps to explain the observation?(A) As the solution evaporates, Cu 2+(aq) andSO42(aq) leave the beaker along with thewater molecules.(B) As the solution evaporates, the dissolution ofCuSO4(s) in the beaker decreases.(C) The evaporation of water is endothermic, somore CuSO4(s) dissolves exothermically inthe solution, which increases the [SO42].(D) As water evaporates, more CuSO 4(s)precipitates out of the solution in the beaker.Unauthorized copying or reuse ofany part of this page is illegal. GO ON TO THE NEXT PAGE.-17-
Solution
The best explanation for the observation that the concentration of SO4^2- does not change over time as the solution evaporates is (D) As water evaporates, more CuSO4(s) precipitates out of the solution in the beaker.
Here's why:
When a solution is saturated, it means that it contains the maximum amount of solute that can be dissolved in the solvent at a given temperature. In this case, the solution is saturated with CuSO4.
As the water (solvent) evaporates, the amount of CuSO4 that can be dissolved in the solution decreases. This is because the solubility of a solute in a solvent is dependent on the amount of solvent present.
Therefore, as the water evaporates, more CuSO4 will precipitate out of the solution to maintain the saturation point. This means that the concentration of CuSO4, and therefore SO4^2-, in the solution will remain constant as the solution evaporates.
This is why option (D) is the best explanation for the observation.
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