Precipitation reactions and solubility rules Transitional Reasoning Download PDF

Questions

1. 1.

   An analytical chemist tests three candidate reagents—dilute $\text{NaCl}(aq)$, $\text{NaOH}(aq)$, and $\text{Na}_2\text{S}(aq)$—to selectively precipitate $\text{Ag}^+(aq)$ from an industrial solution containing equimolar amounts of $\text{Ag}^+$, $\text{Cu}^{2+}$, and $\text{Fe}^{3+}$ ions. The target reagent must remove silver ions as a solid precipitate while leaving both copper(II) and iron(III) ions completely dissolved in the solution. Based on standard solubility rules, which reagent achieves this selective separation, and what is the net ionic equation for the reaction?

   • A) $\text{NaCl}(aq)$, with the net ionic equation $\text{Ag}^+(aq) + \text{Cl}^-(aq) \rightarrow \text{AgCl}(s)$
   • B) $\text{NaOH}(aq)$, with the net ionic equation $\text{Ag}^+(aq) + \text{OH}^-(aq) \rightarrow \text{AgOH}(s)$
   • C) $\text{Na}_2\text{S}(aq)$, with the net ionic equation $2\text{Ag}^+(aq) + \text{S}^{2-}(aq) \rightarrow \text{Ag}_2\text{S}(s)$
   • D) $\text{NaCl}(aq)$, with the net ionic equation $\text{Ag}^+(aq) + \text{Na}^+(aq) + \text{Cl}^-(aq) \rightarrow \text{AgCl}(s) + \text{Na}^+(aq)$
2. 2.

   A student monitors the electrical conductivity of an aqueous solution while gradually adding an equimolar solution of another soluble compound. During the titration, the electrical conductivity drops to near zero at the stoichiometric equivalence point because both cation-anion combinations form insoluble precipitates, leaving virtually no spectator ions in the supernatant liquid. Based on standard solubility rules, which pair of aqueous solutions demonstrates this behavior?

   • A) $\text{AgNO}_3(aq)$ and $\text{KCl}(aq)$
   • B) $\text{CaCl}_2(aq)$ and $\text{Na}_2\text{CO}_3(aq)$
   • C) $\text{Ba(OH)}_2(aq)$ and $\text{CuSO}_4(aq)$
   • D) $\text{Pb(NO}_3)_2(aq)$ and $\text{K}_2\text{SO}_4(aq)$
3. 3.

   A laboratory technician performs separate qualitative tests on three aliquots of an unlabelled, clear aqueous solution containing a single dissolved nitrate salt. Adding aqueous $\text{Na}_2\text{SO}_4$ produces a dense white precipitate, whereas adding aqueous $\text{NaOH}$ produces no visible reaction. In the third test, adding aqueous $\text{Na}_2\text{CO}_3$ forms a white precipitate. Based on standard solubility rules, which compound is present in the unlabelled solution?

   • A) $\text{Mg(NO}_3)_2$
   • B) $\text{Pb(NO}_3)_2$
   • C) $\text{Ba(NO}_3)_2$
   • D) $\text{Fe(NO}_3)_3$
4. 4.

   A student mixes 50 mL of 0.20 M aqueous sodium phosphate, $\text{Na}_3\text{PO}_4(aq)$, with 50 mL of 0.30 M aqueous calcium chloride, $\text{CaCl}_2(aq)$, observing the immediate formation of a white precipitate. After the precipitate settles completely, the mixture is separated by filtration. Based on solubility rules and reaction stoichiometry, which option correctly identifies the chemical formula of the solid precipitate and the predominant ions remaining in the clear filtrate?

   • A) Precipitate: $\text{Ca}_3(\text{PO}_4)_2(s)$; Predominant ions in solution: $\text{Ca}^{2+}(aq)$, $\text{Na}^+(aq)$, and $\text{Cl}^-(aq)$
   • B) Precipitate: $\text{Ca}_3(\text{PO}_4)_2(s)$; Predominant ions in solution: $\text{Na}^+(aq)$ and $\text{Cl}^-(aq)$
   • C) Precipitate: $\text{CaPO}_4(s)$; Predominant ions in solution: $\text{Na}^+(aq)$ and $\text{Cl}^-(aq)$
   • D) Precipitate: $\text{NaCl}(s)$; Predominant ions in solution: $\text{Ca}^{2+}(aq)$ and $\text{PO}_4^{3-}(aq)$
5. 5.

   An environmental chemist analyzes an aqueous industrial runoff sample containing dissolved $\text{Ba(NO}_3)_2$ and $\text{Mg(NO}_3)_2$. The chemist first adds an excess of aqueous $\text{Na}_2\text{SO}_4$, producing a white precipitate that is completely separated by filtration. Next, an excess of aqueous $\text{NaOH}$ is introduced into the remaining clear filtrate, resulting in the formation of a second distinct precipitate. Based on solubility rules, which pair correctly identifies the first and second precipitates formed?

   • A) First: $\text{MgSO}_4$; Second: $\text{Ba(OH)}_2$
   • B) First: $\text{NaNO}_3$; Second: $\text{Mg(OH)}_2$
   • C) First: $\text{BaSO}_4$; Second: $\text{Mg(OH)}_2$
   • D) First: $\text{BaSO}_4$; Second: $\text{NaNO}_3$