Question

State whether \(1 \mathrm{M}\) solutions of the following salts in water would be acidic, basic, or neutral. (a) \(\mathrm{FeCl}_{3}\) (b) \(\mathrm{BaI}_{2}\) (c) \(\mathrm{NH}_{4} \mathrm{NO}_{2}\) (d) \(\mathrm{Na}_{2} \mathrm{HPO}_{4}\) (e) \(\mathrm{K}_{3} \mathrm{PO}_{4}\)

Short answer

Answer: (a) FeCl3 - Acidic, (b) BaI2 - Neutral, (c) NH4NO2 - Acidic, (d) Na2HPO4 - Slightly Basic, (e) K3PO4 - Basic.

Step-by-step solution

Dissociation of the Salt in Water

When a salt is dissolved in water, it dissociates completely into its constituent ions. Write down the dissociation equation for each salt. (a) \(\mathrm{FeCl}_{3} \rightarrow \mathrm{Fe}^{3+} + 3\mathrm{Cl}^-\) (b) \(\mathrm{BaI}_{2} \rightarrow \mathrm{Ba}^{2+} + 2\mathrm{I}^-\) (c) \(\mathrm{NH}_{4} \mathrm{NO}_{2} \rightarrow \mathrm{NH}_{4}^{+} + \mathrm{NO}_{2}^{-}\) (d) \(\mathrm{Na}_{2} \mathrm{HPO}_{4} \rightarrow 2\mathrm{Na}^+ + \mathrm{HPO}_{4}^{2-}\) (e) \(\mathrm{K}_{3} \mathrm{PO}_{4} \rightarrow 3\mathrm{K}^+ + \mathrm{PO}_{4}^{3-}\)

Analyze Interaction with Water

Analyze the ability of the ions produced in Step 1 to react with water and form either H+ or OH- ions. (a) \(\mathrm{Fe}^{3+}\) is a metal ion with high charge density, and it will strongly attract water molecules, which can release \(\mathrm{H}^+\) ions and form \(\mathrm{Fe(OH)}_{n}^{3-n}\) species. The \(\mathrm{Cl}^-\) does not hydrolyze. So, \(\mathrm{FeCl}_{3}\) solution would be acidic. (b) \(\mathrm{Ba}^{2+}\), a group 2 metal ion, does not hydrolyze water significantly, and \(\mathrm{I}^-\) is a weak base. Therefore, \(\mathrm{BaI}_{2}\) has negligible interaction with water, and its solution would be neutral. (c) \(\mathrm{NH}_{4}^{+}\) undergoes hydrolysis reaction with water, releasing \(\mathrm{H}^+\) ions to form \(\mathrm{NH}_{3}\), making the solution acidic. On the other hand, \(\mathrm{NO}_{2}^{-}\) is a weak base and doesn't hydrolyze enough to neutralize the solution completely, keeping it acidic. (d) \(\mathrm{Na}^+\) does not hydrolyze, and \(\mathrm{HPO}_{4}^{2-}\) is a weak base, taking an \(\mathrm{H}^+\) from water and forming \(\mathrm{OH}^{-}\) ions making the solution slightly basic. (e) \(\mathrm{K}^+\) does not hydrolyze, and \(\mathrm{PO}_{4}^{3-}\) is a weak base, taking \(\mathrm{H}^+\) from water and forming \(\mathrm{OH}^{-}\) ions making the solution basic.

Determine According to Interaction with Water

Based on the ions released, determine whether the salt solution will be acidic, basic, or neutral. (a) \(\mathrm{FeCl}_{3}\) - Acidic (b) \(\mathrm{BaI}_{2}\) - Neutral (c) \(\mathrm{NH}_{4} \mathrm{NO}_{2}\) - Acidic (d) \(\mathrm{Na}_{2} \mathrm{HPO}_{4}\) - Slightly Basic (e) \(\mathrm{K}_{3} \mathrm{PO}_{4}\) - Basic