21. Solving a chemistry problem

Test 1. A saturated solution over the precipitate of which substance contains the most C2O42- ions:
a) MgC2O4 PR=8.6 * 10-5 b) NiC2O4 PR=4.0 * 10-10
c) FeC2O4 PR=2.0 * 10-7 d) CaС2O4 PR=6.0 * 10-8
2. Which reagent is the best precipitator of SO42- ions from solutions:
a) Pb(NO3)2 PR PbSO4 = 1.6  10-8 b) CaCl2 PR CaSO4 = 1.0 * 10-5
c) SrCl2 PR SrSO4 = 3.2  10-7 g) Ba(NO3)2 PR BaSO4 = 1.1  10-10
3. Which salt will begin to precipitate earlier when hydrogen sulfide is passed through, if the solution contains Zn2, Hg2, Cd2 and Cu2 ions in equal molar concentrations:
a) ZnS PR=1.610-24 b) HgS PR=1.610-52
c) СdS PR=7.910-27 d) CuS PR=6.0 10-36
4. The solution contains magnesium and calcium ions. With the introduction of which anion in the system will be observed: a) isolated heterogeneous equilibrium; b) combined heterogeneous equilibrium. Which of the two competing processes will prevail (in case b)? (use the tables: “Solubility of bases, acids and salts in water”, “Solubility products of some sparingly soluble electrolytes”.
5. To a saturated aqueous solution of lead (II) sulfide was added:
a) a solution of copper (II) nitrate; b) iron (II) nitrate solution.
Describe possible changes in both cases.
a) PbS PR=1.0*10-27 b) CuS PR=6.0*10-36
c) FeS PR \u003d 5.0 * 10-18