Question

For each of the following precipitation reactions, complete and balance the equation, indicating clearly which product is the precipitate. If no reaction would be expected, so indicate. a. \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}(a q)+\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}(a q) \rightarrow\) b. \(\mathrm{H}_{2} \mathrm{~S}(a q)+\mathrm{NiSO}_{4}(a q) \rightarrow\) c. \(\mathrm{FeCl}_{3}(a q)+\mathrm{NaOH}(a q) \rightarrow\)

Short answer

a. \((NH_4)_{2}SO_4(aq) + Ba(NO_3)_2(aq) \rightarrow BaSO_4(s) + 2 NH_4NO_3(aq)\) b. \(H_2S(aq) + NiSO_4(aq) \rightarrow NiS(s) + H_2SO_4(aq)\) c. \(FeCl_3(aq) + 3 NaOH(aq) \rightarrow Fe(OH)_3(s) + 3 NaCl(aq)\)

Step-by-step solution

Predict the products

To predict the products of this reaction, we will exchange the cations and anions of the reactants: ammonium and sulfate will combine, and barium and nitrate will combine. This results in the formulas: \((NH_4)_{2}SO_4\) and \(Ba(NO_3)_2\).

Check the solubility of the products

Now, we need to check which product is soluble or insoluble using solubility rules. Most sulfates are soluble except those of barium, lead, or silver. So, \(BaSO_4\) is insoluble and will be the precipitate. On the other hand, all nitrates are soluble.

Write the balanced equation

The balanced chemical equation for this precipitation reaction is: \( (NH_4)_{2}SO_4(aq) + Ba(NO_3)_2(aq) \rightarrow BaSO_4(s) + 2 NH_4NO_3(aq) \) b. \(H_{2}S(aq)+NiSO_{4}(a q) \rightarrow\)

Predict the products

First, we'll exchange the cations and anions of the reactants: hydrogen and sulfate will combine, and nickel and sulfide will combine. This results in the formulas: \(H_2SO_4\) and \(NiS\).

Check the solubility of the products

Most sulfides are insoluble except those of group 1 and 2 elements and ammonium. So, \(NiS\) is insoluble and will be the precipitate. All sulfates are soluble except those of barium, lead, or silver; hence, \(H_2SO_4\) is soluble.

Write the balanced equation

The balanced chemical equation for this precipitation reaction is: \( H_2S(aq) + NiSO_4(aq) \rightarrow NiS(s) + H_2SO_4(aq) \) c. \(FeCl_{3}(a q)+NaOH(a q) \rightarrow\)

Predict the products

To predict the products of this reaction, we will exchange the cations and anions of the reactants: iron and hydroxide will combine, and sodium and chloride will combine. This results in the formulas: \(Fe(OH)_3\) and \(NaCl\).

Check the solubility of the products

Hydroxides are insoluble except those of group 1 and 2 elements and ammonium. So, \(Fe(OH)_3\) is insoluble and will be the precipitate. All chloride salts are soluble except those of silver, lead, and mercury; hence, \(NaCl\) is soluble.

Write the balanced equation

The balanced chemical equation for this precipitation reaction is: \(FeCl_3(aq) + 3 NaOH(aq) \rightarrow Fe(OH)_3(s) + 3 NaCl(aq)\)

Key concepts

Chemical Equation Balancing

Balancing chemical equations is akin to solving a puzzle where the number of atoms for each element must be the same on both sides of the equation. It ensures the law of conservation of mass is adhered to, indicating that no atoms are lost or gained in a chemical reaction.
For instance, in the reaction between ammonium sulfate and barium nitrate, the initial unbalanced equation is \( (NH_4)_2SO_4(aq) + Ba(NO_3)_2(aq) \rightarrow BaSO_4(s) + NH_4NO_3(aq) \). Here, we have two ammoniums (\(NH_4^+\)) on the left but only one on the right. By placing a coefficient of 2 in front of \(NH_4NO_3\), we balance the ammoniums and consequently the nitrogens and oxygens. This step is crucial and can be approached by systematically balancing each element and adjusting coefficients until the equation is balanced.

Solubility Rules

Understanding solubility rules enables us to predict whether a substance will dissolve in water, forming an aqueous solution, or form a precipitate. Solubility rules are general guidelines that help forecast the solubility of ionic compounds.

For example, most sulfates are soluble, but barium sulfate is an exception and is insoluble, hence it precipitates out of solution. Likewise, most sulfides are insoluble with a few exceptions, like those of group 1 and 2 elements. These rules help in determining the products in a precipitation reaction, a valuable tool to ensure students are able to accurately predict reaction products even before conducting the experiment.

Predicting Reaction Products

In chemistry, accurately predicting reaction products is a critical skill. When two solutions are mixed, a double displacement reaction often occurs, where the anions and cations exchange partners.

To predict the products, we use both the identities of the reactants and solubility rules. If a product formed is insoluble, it will precipitate out of the solution. For instance, in the equation \(FeCl_3(aq) + NaOH(aq) \rightarrow Fe(OH)_3(s) + NaCl(aq)\), iron(III) hydroxide is formed. Based on solubility rules, hydroxides of iron are insoluble, thus it is the precipitate in this reaction. Being able to predict these products and identify the precipitate is integral for understanding chemical reactions.