Question

Write a net ionic equation for any precipitation reaction that occurs when \(1 \mathrm{M}\) solutions of the following are mixed. (a) copper(II) sulfate and sodium chloride (b) manganese(II) nitrate and ammonium hydroxide (c) silver nitrate and hydrochloric acid (d) nickel(II) sulfate and potassium hydroxide (e) ammonium carbonate and sodium nitrate

Short answer

a) Copper(II) sulfate and sodium chloride b) Manganese(II) nitrate and ammonium hydroxide c) Silver nitrate and hydrochloric acid d) Nickel(II) sulfate and potassium hydroxide e) Ammonium carbonate and sodium nitrate Answer: The reactions that result in the formation of a precipitate are b, c, and d.

Step-by-step solution

(a) Identify possible products

First, we mix copper(II) sulfate \((CuSO_{4})\) and sodium chloride \((NaCl)\). The possible products formed are copper(II) chloride \((CuCl_{2})\) and sodium sulfate \((Na_{2}SO_{4})\).

(a) Determine insoluble products

According to solubility rules, both copper(II) chloride and sodium sulfate are soluble in water, so there is no precipitation reaction in this case.

(b) Identify possible products

Next, we mix manganese(II) nitrate \((Mn(NO_{3})_{2})\) and ammonium hydroxide \((NH_{4}OH)\). The possible products formed are manganese(II) hydroxide \((Mn(OH)_{2})\) and ammonium nitrate \((NH_{4}NO_{3})\).

(b) Determine insoluble products

According to solubility rules, manganese(II) hydroxide is insoluble, while ammonium nitrate is soluble. Therefore, a precipitation reaction occurs, and we need to write the net ionic equation for it.

(b) Write net ionic equation

The ionic equation is: \(Mn^{2+} + 2NO_{3}^{-} + 2NH_{4}^{+} + 2OH^{-} \rightarrow Mn(OH)_{2} + 2NH_{4}^{+} + 2NO_{3}^{-}\) The net ionic equation (removing spectator ions) is: \(Mn^{2+} + 2OH^{-} \rightarrow Mn(OH)_{2}\)

(c) Identify possible products

We mix silver nitrate \((AgNO_{3})\) and hydrochloric acid \((HCl)\). The possible products formed are silver chloride \((AgCl)\) and nitric acid \((HNO_{3})\).

(c) Determine insoluble products

According to solubility rules, silver chloride is insoluble, while nitric acid is soluble. Therefore, a precipitation reaction occurs, and we need to write the net ionic equation for it.

(c) Write net ionic equation

The ionic equation is: \(Ag^{+} + NO_{3}^{-} + H^{+} + Cl^{-} \rightarrow AgCl + H^{+} + NO_{3}^{-}\) The net ionic equation (removing spectator ions) is: \(Ag^{+} + Cl^{-} \rightarrow AgCl\)

(d) Identify possible products

We mix nickel(II) sulfate \((NiSO_{4})\) and potassium hydroxide \((KOH)\). The possible products formed are nickel(II) hydroxide \((Ni(OH)_{2})\) and potassium sulfate \((K_{2}SO_{4})\).

(d) Determine insoluble products

According to solubility rules, nickel(II) hydroxide is insoluble, while potassium sulfate is soluble. Therefore, a precipitation reaction occurs, and we need to write the net ionic equation for it.

(d) Write net ionic equation

The ionic equation is: \(Ni^{2+} + SO_{4}^{2-} + 2K^{+} + 2OH^{-} \rightarrow Ni(OH)_{2} + 2K^{+} + SO_{4}^{2-}\) The net ionic equation (removing spectator ions) is: \(Ni^{2+} + 2OH^{-} \rightarrow Ni(OH)_{2}\)

(e) Identify possible products

We mix ammonium carbonate \((NH_{4}_{2}CO_{3})\) and sodium nitrate \((NaNO_{3})\). The possible products formed are sodium carbonate \((Na_{2}CO_{3})\) and ammonium nitrate \((NH_{4}NO_{3})\).

(e) Determine insoluble products

According to solubility rules, both sodium carbonate and ammonium nitrate are soluble in water, so there is no precipitation reaction in this case.

Key concepts

Precipitation Reaction

A precipitation reaction occurs when two aqueous solutions react to form an insoluble solid, known as a precipitate. This type of reaction is a hallmark of double-displacement reactions, where the cations and anions of two different compounds exchange partners.

For example, consider the reaction between silver nitrate \(AgNO_3\) and hydrochloric acid \(HCl\). When these two solutions are mixed, silver ions \(Ag^+\) combine with chloride ions \(Cl^-\) to form silver chloride \(AgCl\), a white solid that precipitates out of the solution. The equation for this reaction is:

\[\begin{align*}AgNO_3 \text{ (aq) } + HCl \text{ (aq) } &\rightarrow AgCl \text{ (s) } + HNO_3 \text{ (aq) }\end{align*}\]

Precipitation reactions are not only essential in the laboratory for the removal of certain ions from a solution but also have practical applications such as in wastewater treatment, where unwanted dissolved substances are removed through precipitation.

Solubility Rules

Solubility rules are a set of guidelines used to predict whether a compound will dissolve in water, forming an aqueous solution, or remain undissolved as a solid precipitate. These rules play a significant role in determining the outcome of precipitation reactions.

Understanding solubility rules helps us foresee which combinations of ionic compounds will lead to the formation of a precipitate. For example, most sulfate salts are soluble, except for those of barium, lead(II), mercury(II), and calcium to some extent. This is why in the reaction between nickel(II) sulfate \(NiSO_4\) and potassium hydroxide \(KOH\), only nickel(II) hydroxide \(Ni(OH)_2\) precipitates, as hydroxides are mostly insoluble with a few exceptions such as those of the alkali metals.

There isn't a comprehensive rule that applies to all ionic compounds, which is why knowing the common solubility rules is indispensable for anyone studying chemistry and chemical reactions.

Spectator Ions

Spectator ions are ions that exist in the same form on both the reactant and product sides of a chemical equation. They do not participate in the chemical reaction and therefore do not affect the outcome of the reaction.

In the net ionic equation, we remove spectator ions to simplify the equation and highlight the actual chemical change. For instance, in the full ionic equation for the reaction between manganese(II) nitrate \(Mn(NO_3)_2\) and ammonium hydroxide \(NH_4OH\):

\[Mn^{2+} + 2NO_3^{-} + 2NH_4^{+} + 2OH^{-} \rightarrow Mn(OH)_2 + 2NH_4^{+} + 2NO_3^{-}\]

The ammonium \(NH_4^{+}\) and nitrate \(NO_3^{-}\) ions are spectator ions, as they do not change and remain in solution. Removing them provides the net ionic equation:

\[Mn^{2+} + 2OH^{-} \rightarrow Mn(OH)_2\]

It is the \(Mn^{2+}\) and \(OH^{-}\) ions that actually react to form the insoluble manganese(II) hydroxide \(Mn(OH)_2\). Identifying spectator ions is crucial in simplifying complex reactions and in understanding the reaction mechanics at the ionic level.