Question

Will precipitation occur when the following solutions are mixed? If so, write a balanced chemical equation for the reac- tion. (a) \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) and \(\mathrm{AgNO}_{3},\) (b) \(\mathrm{NaNO}_{3}\) and \(\mathrm{NiSO}_{4}\), (c) \(\mathrm{FeSO}_{4}\) and \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}\).

Short answer

(a) Yes, precipitation will occur, forming \(\mathrm{Ag}_{2}\mathrm{CO}_{3}\). The balanced equation is: \[\mathrm{2AgNO}_{3}(\mathrm{aq})+\mathrm{Na}_{2}\mathrm{CO}_{3}(\mathrm{aq})\rightarrow \mathrm{2NaNO}_{3}(\mathrm{aq})+\mathrm{Ag}_{2}\mathrm{CO}_{3}(\mathrm{s})\] (b) No precipitation will occur. (c) Yes, precipitation will occur, forming \(\mathrm{PbSO}_{4}\). The balanced equation is: \[\mathrm{FeSO}_{4}(\mathrm{aq})+\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})\rightarrow \mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+\mathrm{PbSO}_{4}(\mathrm{s})\]

Step-by-step solution

(a) Mixing \(\mathrm{Na}_{2}\mathrm{CO}_{3}\) and \(\mathrm{AgNO}_{3}\)

When the two solutions are mixed, the possible products are \(\mathrm{NaNO}_{3}\) and \(\mathrm{Ag}_{2}\mathrm{CO}_{3}\). According to the solubility rules, most nitrates are soluble, and most carbonates are insoluble except for those of Group 1A elements and \(\mathrm{NH}_{4}^{+}\). Therefore, \(\mathrm{NaNO}_{3}\) will be soluble, and \(\mathrm{Ag}_{2}\mathrm{CO}_{3}\) will be insoluble and form a precipitate. The balanced chemical equation for this reaction is: \[\mathrm{2AgNO}_{3}(\mathrm{aq})+\mathrm{Na}_{2}\mathrm{CO}_{3}(\mathrm{aq})\rightarrow \mathrm{2NaNO}_{3}(\mathrm{aq})+\mathrm{Ag}_{2}\mathrm{CO}_{3}(\mathrm{s})\]

(b) Mixing \(\mathrm{NaNO}_{3}\) and \(\mathrm{NiSO}_{4}\)

When the two solutions are mixed, the possible products are \(\mathrm{Na}_{2}\mathrm{SO}_{4}\) and \(\mathrm{Ni}\left(\mathrm{NO}_{3}\right)_{2}\). According to the solubility rules, most nitrates and most sulfates are soluble. Both \(\mathrm{Na}_{2}\mathrm{SO}_{4}\) and \(\mathrm{Ni}\left(\mathrm{NO}_{3}\right)_{2}\) are soluble, so no precipitate will form in this reaction. Since there is no precipitation, we do not need to write a balanced chemical equation for this reaction.

(c) Mixing \(\mathrm{FeSO}_{4}\) and \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}\)

When the two solutions are mixed, the possible products are \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}\) and \(\mathrm{PbSO}_{4}\). According to the solubility rules, most nitrates are soluble, and most sulfates are soluble except for those of \(\mathrm{Ba^{2+}}\), \(\mathrm{Pb^{2+}}\), \(\mathrm{Hg_{2}^{2+}}\), and \(\mathrm{Sr^{2+}}\). Therefore, \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}\) will be soluble, and \(\mathrm{PbSO}_{4}\) will be insoluble and form a precipitate. The balanced chemical equation for this reaction is: \[\mathrm{FeSO}_{4}(\mathrm{aq})+\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})\rightarrow \mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+\mathrm{PbSO}_{4}(\mathrm{s})\]

Key concepts

Precipitation Reaction

Understanding precipitation reactions is key to mastering the interactions in aqueous solutions. In a precipitation reaction, two soluble salts are mixed together to form at least one insoluble product, known as the precipitate.

For example, when a solution of sodium carbonate ((Na_{2}CO_{3})) and silver nitrate (AgNO_{3}) are mixed, a white solid of silver carbonate (Ag_{2}CO_{3}) forms as the precipitate. This type of chemical process is critical in various fields, including environmental science for water purification, and in industries such as pharmaceutical production where purity is essential.

In the exercise given, the formation of Ag_{2}CO_{3} indicates a classic precipitation reaction. Similarly, the creation of an insoluble lead sulfate (PbSO_{4}) from the mixture of iron sulfate (FeSO_{4}) and lead nitrate (Pb(NO_{3})_2) backs up the occurrence of such a reaction. Identifying a precipitate depends on the solubility rules, which predict whether an ionic compound will dissolve or form a solid in water.

Balanced Chemical Equation

A balanced chemical equation is a representation that shows the exact proportions of reactants and products in a chemical reaction. It follows the law of conservation of mass, meaning the quantity of each element does not change in a chemical reaction. Thus, each element must have the same number of atoms on both sides of the equation.

When writing equations for precipitation reactions, balance is essential. As illustrated in the provided examples, the balanced equation for the reaction between sodium carbonate and silver nitrate is 2AgNO_{3}(aq) + Na_{2}CO_{3}(aq) ⟶ 2NaNO_{3}(aq) + Ag_{2}CO_{3}(s). It shows that two silver (Ag) atoms and one carbonate (CO_3^{2-}) pair with two nitrate (NO_3^-) groups and two sodium (Na) atoms to ensure mass is conserved.

The balanced equations provide a clear picture of the stoichiometry of a reaction, which is essential not only for understanding the reaction itself but also for making calculations related to yields and reactant consumption.

Soluble and Insoluble Compounds

The solubility rules are vital for determining which compounds will dissolve in water (soluble) and which will not (insoluble or slightly soluble). Soluble compounds will dissociate, forming ions in solution. Insoluble compounds, on the other hand, will not dissolve and often form a precipitate in a reaction.

For instance, most compounds of Group 1A elements and ammonium (NH_4^+) are soluble. In contrast, carbonates (CO_3^{2-}) and phosphates (PO_4^{3-}) are usually insoluble, with exceptions for compounds with Group 1A elements and ammonium. Compounds containing nitrate (NO_3^-) or sulfate (SO_4^{2-}) are generally soluble, with some exceptions, such as lead sulfate (PbSO_4), which is insoluble.

In the exercises, the nickel sulfate (NiSO_{4}) and sodium nitrate (NaNO_{3}) remain in solution since they follow the rule that most sulfates and nitrates are soluble. Meanwhile, silver carbonate (Ag_{2}CO_{3}) and lead sulfate (PbSO_{4}) are insoluble, leading to them forming a precipitate and hence a visible reaction. These rules help streamline the study of chemical reactions and allow prediction of outcomes before they are even mixed.