Question

Give an example how each of the following insoluble ionic compounds could be produced using a precipitation reaction. Write the balanced formula equation for each reaction. a. \(\mathrm{Fe}(\mathrm{OH})_{3}(s)\) b. \(\mathrm{Hg}_{2} \mathrm{Cl}_{2}(s)\) c. \(\mathrm{PbSO}_{4}(s)\) d. \(\mathrm{BaCrO}_{4}(s)\)

Short answer

a. \( \mathrm{Fe(NO_{3})_{3}(aq) + 3NaOH(aq) \to Fe(OH)_{3}(s) + 3NaNO_{3}(aq)} \) b. \( \mathrm{Hg_{2}(NO_{3})_{2}(aq) + 2NaCl(aq) \to Hg_{2}Cl_{2}(s) + 2NaNO_{3}(aq)} \) c. \( \mathrm{Pb(NO_{3})_{2}(aq) + Na_{2}SO_{4}(aq) \to PbSO_{4}(s) + 2NaNO_{3}(aq)} \) d. \( \mathrm{Ba(NO_{3})_{2}(aq) + K_{2}CrO_{4}(aq) \to BaCrO_{4}(s) + 2KNO_{3}(aq)} \)

Step-by-step solution

a. Production of \(\mathrm{Fe}(\mathrm{OH})_{3}\)(s) by precipitation reaction

In order to produce \(\mathrm{Fe}(\mathrm{OH})_{3}\)(s), we will need an aqueous solution containing Fe(III) ions and another containing hydroxide ions. We can choose, for example, \(\mathrm{Fe}(\mathrm{NO}_{3})_{3}(\aq)\) as a source of Fe(III) ions and \(\mathrm{NaOH}(\aq)\) as a source of hydroxide ions. The reaction would be: \[\mathrm{Fe(NO_{3})_{3}(aq) + 3NaOH(aq) \to Fe(OH)_{3}(s) + 3NaNO_{3}(aq)}\]

b. Production of \(\mathrm{Hg_{2}Cl_{2}}\)(s) by precipitation reaction

In order to produce \(\mathrm{Hg_{2}Cl_{2}}\)(s), we will need an aqueous solution containing Hg(I) ions and another containing chloride ions. We can choose, for example, \(\mathrm{Hg_{2}(NO_{3})_{2}(\aq)}\) as a source of Hg(I) ions and \(\mathrm{NaCl(aq)}\) as a source of chloride ions. The reaction would be: \[\mathrm{Hg_{2}(NO_{3})_{2}(aq) + 2NaCl(aq) \to Hg_{2}Cl_{2}(s) + 2NaNO_{3}(aq)}\]

c. Production of \(\mathrm{PbSO_{4}}\)(s) by precipitation reaction

In order to produce \(\mathrm{PbSO_{4}}\)(s), we will need an aqueous solution containing Pb(II) ions and another containing sulfate ions. We can choose, for example, \(\mathrm{Pb(NO_{3})_{2}(aq)}\) as a source of Pb(II) ions and \(\mathrm{Na_{2}SO_{4}(aq)}\) as a source of sulfate ions. The reaction would be: \[\mathrm{Pb(NO_{3})_{2}(aq) + Na_{2}SO_{4}(aq) \to PbSO_{4}(s) + 2NaNO_{3}(aq)}\]

d. Production of \(\mathrm{BaCrO_{4}}\)(s) by precipitation reaction

In order to produce \(\mathrm{BaCrO_{4}}\)(s), we will need an aqueous solution containing Ba(II) ions and another containing chromate ions. We can choose, for example, \(\mathrm{Ba(NO_{3})_{2}(aq)}\) as a source of Ba(II) ions and \(\mathrm{K_{2}CrO_{4}(aq)}\) as a source of chromate ions. The reaction would be: \[\mathrm{Ba(NO_{3})_{2}(aq) + K_{2}CrO_{4}(aq) \to BaCrO_{4}(s) + 2KNO_{3}(aq)}\]

Key concepts

insoluble ionic compounds

Insoluble ionic compounds are substances that do not dissolve significantly in water. An ionic compound typically forms when a metal reacts with a non-metal, resulting in the formation of crystals held together by ionic bonds. However, not all of these compounds dissolve well in water. Their insolubility depends on the strength of the attraction between the ions compared to their interaction with water molecules.
When certain ions from different aqueous solutions combine, they may create a solid that does not dissolve, known as a precipitate. This is the essence of a precipitation reaction.
Some examples of insoluble ionic compounds include:

• Iron(III) hydroxide
• Mercury(I) chloride
• Lead(II) sulfate
• Barium chromate

These compounds are typically formed when solutions containing specific ions are combined, resulting in the formation of the solid precipitate.

balanced chemical equations

A balanced chemical equation accurately represents the conservation of mass in a chemical reaction. It ensures that the same number of each type of atom is on both sides of the equation, which reflects the law of conservation of mass.
In a precipitation reaction, it's important to write a balanced chemical equation to show the precise exchange of ions that leads to the formation of an insoluble product. For instance, while forming he chemical equation should reflect the precise stoichiometry: \[\text{Fe(NO}_3\text{)}_3(\text{aq}) + 3\text{NaOH(\text{aq})} \rightarrow \text{Fe(OH)}_3(\text{s}) + 3\text{NaNO}_3(\text{aq})\]Balancing chemical equations:

• Ensures that identical atoms feature equally on both sides.
• Creates clarity when predicting the amounts of reactants needed.
• Avoids errors in laboratory preparation through a clear depiction of reactions.

aqueous solutions

Aqueous solutions are mixtures where water is the solvent. They are essential in precipitation reactions because they allow ions to move freely and interact to form products. In such solutions, ionic compounds dissociate into their individual ions.
This dissociation is crucial for precipitation reactions, as it allows the necessary ions to meet and produce a precipitate. For example, in the formation of lead(II) sulfate:\[\text{Pb(NO}_3\text{)}_2(\text{aq}) + \text{Na}_2\text{SO}_4(\text{aq}) \rightarrow \text{PbSO}_4(\text{s}) + 2\text{NaNO}_3(\text{aq})\]In this process:

• Lead(II) nitrate dissociates to provide lead ions.
• Sodium sulfate dissociates to provide sulfate ions.
• These ions meet in the solution and form an insoluble precipitate of lead(II) sulfate.

The process also frequently releases heat as ions re-order from an aqueous environment to a solid state.

production of precipitates

The production of precipitates involves forming a solid from solution during a chemical reaction. This happens when the product of the ions' concentration in the solution exceeds the compound's solubility product constant. Essentially, when the solution can no longer keep the ionic products dissolved, they come together to form a solid precipitate.
Precipitation reactions are vital in many lab applications, including:

• Purification of elements or compounds.
• Removal of ions from water systems.
• Qualitative chemical analysis to identify components in a mixture.

For instance, combining barium nitrate and potassium chromate in aqueous solutions leads to the production of barium chromate precipitate:\[\text{Ba(NO}_3)_2(\text{aq}) + \text{K}_2\text{CrO}_4(\text{aq}) \rightarrow \text{BaCrO}_4(\text{s}) + 2\text{KNO}_3(\text{aq})\]In summary, precipitate formation occurs when the ions settle into a grid-like arrangement typical of a crystal structure, distinct and separate from the liquid medium.