Problem 73 - Chemistry: An Atoms-Focused Approach

Question

Which, if any, aqueous solutions of the following chloride compounds are acidic? (a) \(\mathrm{CaCl}_{2} ;\) (b) \(\mathrm{CrCl}_{3} ;\) (c) \(\mathrm{NaCl}\) (d) \(\mathrm{FeCl}_{3}\)

Step-by-Step Solution

Answer

Answer: The acidic aqueous solutions are formed by (b) CrCl₃ and (d) FeCl₃.

Step 1: (a) Analyzing \(\mathrm{CaCl}_{2}\)

For \(\mathrm{CaCl}_{2}\), Calcium (Ca²⁺) is not a highly electronegative ion, and its bond with chloride ions (Cl⁻) is an ionic bond. When dissolved in water, it forms: \(\mathrm{CaCl}_2 \rightarrow \mathrm{Ca^{2+}} + 2\mathrm{Cl^-}\) Neither the calcium nor the chloride ions can produce H₃O⁺ in water. Therefore, the solution will not create an acidic solution.

Step 2: (b) Analyzing \(\mathrm{CrCl}_{3}\)

For \(\mathrm{CrCl}_{3}\), Chromium (Cr³⁺) is a transition metal with higher electronegativity compared to \(\mathrm{Ca^{2+}}\). When dissolved in water, it forms: \(\mathrm{CrCl}_3 \rightarrow \mathrm{Cr^{3+}} + 3\mathrm{Cl^-}\) Chromium ions (\(\mathrm{Cr^{3+}}\)) can hydrolyze by removing protons (H⁺) from water molecules, which leads to an increase in H₃O⁺ concentration: \(\mathrm{Cr^{3+}} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{Cr}(\mathrm{OH})^{2+} + \mathrm{H_3O^+}\) Therefore, the solution of \(\mathrm{CrCl}_{3}\) will be acidic.

Step 3: (c) Analyzing \(\mathrm{NaCl}\)

For \(\mathrm{NaCl}\), Sodium (Na⁺) is not a highly electronegative ion, and its bond with chloride ions (Cl⁻) is an ionic bond. When dissolved in water, it forms: \(\mathrm{NaCl} \rightarrow \mathrm{Na^+} + \mathrm{Cl^-}\) Neither the sodium nor the chloride ions can produce H₃O⁺ in water. Therefore, the solution will not create an acidic solution.

Step 4: (d) Analyzing \(\mathrm{FeCl}_{3}\)

For \(\mathrm{FeCl}_{3}\), Iron (Fe³⁺) is a transition metal with higher electronegativity compared to \(\mathrm{Ca^{2+}}\). When dissolved in water, it forms: \(\mathrm{FeCl}_3 \rightarrow \mathrm{Fe^{3+}} + 3\mathrm{Cl^-}\) Iron ions (\(\mathrm{Fe^{3+}}\)) can hydrolyze by removing protons (H⁺) from water molecules, which leads to an increase in H₃O⁺ concentration: \(\mathrm{Fe^{3+}} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{Fe}(\mathrm{OH})^{2+} + \mathrm{H_3O^+}\) Therefore, the solution of \(\mathrm{FeCl}_{3}\) will be acidic. In conclusion, the aqueous solutions of \(\mathrm{CrCl}_{3}\) and \(\mathrm{FeCl}_{3}\) are acidic.