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Aqueous Equilibria · Part 4 of 4
12 exam-style questions with model answers, plus 16 quick multi-choice questions — every question on this part of the standard, grouped by the 4 pages of notes they come from.
Write a full answer before you reveal the model one. That comparison is where the learning happens.
Write the equation for the equilibrium in a saturated solution of lead(II) iodide, PbI2, and the expression for its Ks.
Calculate the solubility of calcium fluoride, CaF2, in mol L−1, given Ks = 3.9 × 10−11, and state the concentration of each ion in the saturated solution.
A student is given Ks(AgCl) = 1.8 × 10−10 and Ks(Ag2CrO4) = 1.1 × 10−12. They conclude that silver chromate is about 160 times less soluble than silver chloride. Evaluate this conclusion, and explain the general circumstances under which Ks values may and may not be compared directly.
State what Q represents and the rule for using it to predict whether a precipitate will form.
20.0 mL of 0.0010 mol L−1 Pb(NO3)2 is mixed with 30.0 mL of 0.0020 mol L−1 KI. Predict by calculation whether a precipitate of PbI2 forms. Ks(PbI2) = 7.1 × 10−9
A student mixes 20.0 mL of 0.0188 mol L−1 AgNO3 with 30.0 mL of 0.0146 mol L−1 Al2(SO4)3 and calculates Q for Ag2SO4 as (0.0188)2(0.0146) = 5.16 × 10−6, concluding that since this is less than Ks = 1.20 × 10−5, no precipitate forms. Identify every error in this calculation, perform it correctly, and state the correct conclusion.
Explain what is meant by the common ion effect, and state its effect on the solubility of a sparingly soluble solid and on its Ks.
Calculate the solubility of Ag2CrO4 in 0.10 mol L−1 AgNO3, and compare it with its solubility in pure water. Ks(Ag2CrO4) = 1.1 × 10−12
A saturated solution of Ag2SO4 is prepared. Four solutions of equal concentration are available: HNO3, Na2SO4, NH3 and KNO3. Predict and justify the effect of adding each on the solubility of Ag2SO4, including any relevant equations.
State two ways of making a sparingly soluble solid dissolve further, and explain in one sentence why each works.
Explain, with equations, why silver chloride dissolves in aqueous ammonia but not in dilute nitric acid.
Sodium hydroxide solution is added dropwise to a solution containing Zn2+ ions. A white precipitate forms, which then dissolves as more NaOH is added. Explain both observations with equations, and explain why the same experiment with Mg2+ would give a precipitate that does not redissolve.