Problem 23 - Chemistry: The Central Science

Question

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

Step-by-Step Solution

Answer

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

Step 1: (a) Identify possible products

First, identify the cations and anions in the given solutions for (a): \(\mathrm{Na}_{2}\mathrm{CO}_{3}\) and \(\mathrm{AgNO}_{3}\). For \(\mathrm{Na}_{2}\mathrm{CO}_{3}\), the cation is \(\mathrm{Na}^{+}\) and the anion is \(\mathrm{CO}_{3}^{2-}\). For \(\mathrm{AgNO}_{3}\), the cation is \(\mathrm{Ag}^{+}\) and the anion is \(\mathrm{NO}_{3}^{-}\).

Step 2: (a) Check solubility rules and identify precipitate

According to the solubility rules, \(\mathrm{CO}_{3}^{2-}\) and most of the \(\mathrm{NO}_{3}^{-}\) salts are soluble, except for the salts containing \(\mathrm{Ag}^+\). Therefore, a possible precipitate contains \(\mathrm{Ag}^+\) and \(\mathrm{CO}_{3}^{2-}\), resulting in \(\mathrm{Ag}_{2}\mathrm{CO}_{3}\), which is an insoluble product.

Step 3: (a) Write balanced chemical equation

Write the balanced chemical equation for the precipitation reaction between \(\mathrm{Na}_{2}\mathrm{CO}_{3}\) and \(\mathrm{AgNO}_{3}\): \[2\,\mathrm{AgNO}_{3}(aq) + \mathrm{Na}_{2}\mathrm{CO}_{3}(aq) \rightarrow \mathrm{Ag}_{2}\mathrm{CO}_{3}(s) + 2\,\mathrm{NaNO}_{3}(aq)\]

Step 4: (b) Identify possible products

First, identify the cations and anions in the given solutions for (b): \(\mathrm{NaNO}_{3}\) and \(\mathrm{NiSO}_{4}\). For \(\mathrm{NaNO}_{3}\), the cation is \(\mathrm{Na}^{+}\) and the anion is \(\mathrm{NO}_{3}^{-}\). For \(\mathrm{NiSO}_{4}\), the cation is \(\mathrm{Ni}^{2+}\) and the anion is \(\mathrm{SO}_{4}^{2-}\).

Step 5: (b) Check solubility rules and identify precipitate

According to the solubility rules, most \(\mathrm{NO}_{3}^{-}\) and \(\mathrm{SO}_{4}^{2-}\) salts are soluble. Therefore, a reaction does not occur because neither \(\mathrm{Na}_{2}\mathrm{SO}_{4}\) nor \(\mathrm{Ni}\left(\mathrm{NO}_{3}\right)_{2}\) are insoluble salts.

Step 6: (c) Identify possible products

First, identify the cations and anions in the given solutions for (c): \(\mathrm{FeSO}_{4}\) and \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}\). For \(\mathrm{FeSO}_{4}\), the cation is \(\mathrm{Fe}^{2+}\) and the anion is \(\mathrm{SO}_{4}^{2-}\). For \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}\), the cation is \(\mathrm{Pb}^{2+}\) and the anion is \(\mathrm{NO}_{3}^{-}\).

Step 7: (c) Check solubility rules and identify precipitate

According to the solubility rules, most \(\mathrm{NO}_{3}^{-}\) salts are soluble; however, some \(\mathrm{SO}_{4}^{2-}\) salts are insoluble. Therefore, a possible precipitate contains \(\mathrm{Pb}^{2+}\) and \(\mathrm{SO}_{4}^{2-}\), resulting in \(\mathrm{PbSO}_{4}\), which is an insoluble product.

Step 8: (c) Write balanced chemical equation

Write the balanced chemical equation for the precipitation reaction between \(\mathrm{FeSO}_{4}\) and \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}\): \[\mathrm{FeSO}_{4}(aq) + \mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(aq) \rightarrow \mathrm{PbSO}_{4}(s) + \mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}(aq)\]

Key Concepts

Precipitation Reactions

Precipitation reactions occur when two aqueous solutions are mixed, and an insoluble solid, known as a precipitate, forms. This is often the result of an exchange of ions between the reacting solutions.
Such reactions are a key part of many analysis methods in chemistry, enabling the separation and identification of different substances.When two solutions containing soluble salts are mixed, there can be various outcomes:

• If no combination of ions forms an insoluble compound, no precipitate occurs.
• If a combination of ions results in an insoluble compound, that compound will precipitate.

In the presented exercise, precipitation took place in the cases involving \(\text{AgNO}_{3}\) with \(\text{Na}_{2}\text{CO}_{3}\), where \(\text{Ag}_{2}\text{CO}_{3}\) forms, and \(\text{FeSO}_{4}\) with \(\text{Pb}\left(\text{NO}_{3}\right)_{2}\), resulting in \(\text{PbSO}_{4}\).Identifying whether a reaction will form a precipitate is often aided by the application of solubility rules, which can predict the solubility of various ionic compounds.

Solubility Rules

Solubility rules are guidelines that chemists use to predict whether an ionic compound will dissolve or form a precipitate in water.
While there are many specific rules, some general ones are particularly helpful.Key solubility rules include:

• Most nitrates (NO₃^-) are soluble.
• Most salts containing alkali metal cations (such as Na⁺, K⁺) and ammonium ion (NH₄⁺) are soluble.
• Most carbonate (CO₃^2-), phosphate (PO₄^3-), oxide (O^2-), and hydroxide (OH^-) salts are insoluble, except when paired with alkali metals or ammonium.
• All common lead, silver, and mercury salts are generally insoluble, except for their nitrates, and perchlorates.
• Most sulfates (SO₄^2-) are soluble, except for those of barium, calcium, lead, and strontium.

These rules help in determining the outcome of potential precipitation reactions. For instance, in the given exercise, the solubility rules helped illustrate why \(\text{Ag}_{2}\text{CO}_{3}\) and \(\text{PbSO}_{4}\) precipitated from their respective reactions.

Balanced Chemical Equations

A balanced chemical equation represents a chemical reaction using the formulas of the reactants and products. It provides insight into the stoichiometry of the reaction, ensuring the conservation of mass by having the same number of each type of atom on both sides of the equation.
In the context of precipitation reactions, a balanced equation also reflects which compounds are dissolved in water (aqueous) and which form a solid precipitate.Balanced equations are structured as follows:

• Reactants are placed on the left, products on the right.
• Coefficients in front of formulas ensure equal numbers of atoms for each element on both sides.
• State symbols (such as (aq) for aqueous and (s) for solid) indicate the states of substances.

The provided solutions included these balanced chemical equations:\[2\,\text{AgNO}_{3}(aq) + \text{Na}_{2}\text{CO}_{3}(aq) \rightarrow \text{Ag}_{2}\text{CO}_{3}(s) + 2\,\text{NaNO}_{3}(aq)\]\[\text{FeSO}_{4}(aq) + \text{Pb}\left(\text{NO}_{3}\right)_{2}(aq) \rightarrow \text{PbSO}_{4}(s) + \text{Fe}\left(\text{NO}_{3}\right)_{2}(aq)\]Such equations not only reflect the substances involved but also guide in quantitative analysis for reactions, helping students internalize the crucial skill of equation balancing in chemistry.