Question

On the basis of the general solubility rules given in Table 7.1 , predict the identity of the precipitate that forms when aqueous solutions of the following substances are mixed. If no precipitate is likely, indicate which rules apply. a. copper(II) chloride, \(\mathrm{CuCl}_{2}\), and ammonium sulfide, \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{~S}\) b. barium nitrate, \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2},\) and potassium phosphate, \(\mathrm{K}_{3} \mathrm{PO}_{4}\) c. silver acetate, \(\mathrm{AgC}_{2} \mathrm{H}_{3} \mathrm{O}_{2},\) and calcium chloride, \(\mathrm{CaCl}_{2}\) d. potassium carbonate, \(\mathrm{K}_{2} \mathrm{CO}_{3}\), and cobalt(II) chloride, \(\mathrm{CoCl}_{2}\) e. sulfuric acid, \(\mathrm{H}_{2} \mathrm{SO}_{4},\) and calcium nitrate, \(\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}\) f. mercurous acetate, \(\mathrm{Hg}_{2}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2},\) and hydrochloric acid, \(\mathrm{HCl}\)

Short answer

The precipitates formed when the given pairs of aqueous solutions are mixed are as follows: a. Copper(II) sulfide (CuS) b. Barium phosphate (Ba₃(PO₄)₂) c. Silver chloride (AgCl) d. Cobalt(II) carbonate (CoCO₃) e. Calcium sulfate (CaSO₄) f. Mercury(I) chloride (Hg₂Cl₂)

Step-by-step solution

Write the chemical formulas of the reactants

CuCl₂ and (NH₄)₂S

Analyze the solubility rules

Based on rule 6, most sulfides are insoluble except for those of alkali metals, ammonium, and groups 2A and 3A. Copper(II) sulfide is not an exception; thus, it is insoluble.

Write the chemical formulas of the products and predict the precipitate

The products will be Copper(II) sulfide (CuS) and ammonium chloride (NH₄Cl). CuS is expected to be the precipitate. The precipitate formed is copper(II) sulfide (CuS). #b. Barium nitrate and potassium phosphate#

Write the chemical formulas of the reactants

Ba(NO₃)₂ and K₃PO₄

Analyze the solubility rules

Based on rule 4, most phosphates are insoluble, except for those of alkali metals and ammonium. Barium phosphate is not an exception, so it's insoluble.

Write the chemical formulas of the products and predict the precipitate

The products will be Barium phosphate (Ba₃(PO₄)₂) and potassium nitrate (KNO₃). Ba₃(PO₄)₂ is expected to be the precipitate. The precipitate formed is barium phosphate (Ba₃(PO₄)₂). #c. Silver acetate and calcium chloride#

Write the chemical formulas of the reactants

AgC₂H₃O₂ and CaCl₂

Analyze the solubility rules

Based on rule 3, most chlorides are soluble, except for those of silver, lead, and mercury(I). Silver chloride is an exception, so it's insoluble.

Write the chemical formulas of the products and predict the precipitate

The products will be Silver chloride (AgCl) and calcium acetate (Ca(C₂H₃O₂)₂). AgCl is expected to be the precipitate. The precipitate formed is silver chloride (AgCl). #d. Potassium carbonate and cobalt(II) chloride#

Write the chemical formulas of the reactants

K₂CO₃ and CoCl₂

Analyze the solubility rules

Based on rule 4, most carbonates are insoluble, except for those of alkali metals and ammonium. Cobalt(II) carbonate is not an exception, so it's insoluble.

Write the chemical formulas of the products and predict the precipitate

The products will be Cobalt(II) carbonate (CoCO₃) and potassium chloride (KCl). CoCO₃ is expected to be the precipitate. The precipitate formed is cobalt(II) carbonate (CoCO₃). #e. Sulfuric acid and calcium nitrate#

Write the chemical formulas of the reactants

H₂SO₄ and Ca(NO₃)₂

Analyze the solubility rules

Based on rule 5, most sulfates are soluble, except for those of calcium, strontium, barium, and lead. Calcium sulfate is an exception, so it's insoluble.

Write the chemical formulas of the products and predict the precipitate

The products will be Calcium sulfate (CaSO₄) and nitric acid (HNO₃). CaSO₄ is expected to be the precipitate. The precipitate formed is calcium sulfate (CaSO₄). #f. Mercurous acetate and hydrochloric acid#

Write the chemical formulas of the reactants

Hg₂(C₂H₃O₂)₂ and HCl

Analyze the solubility rules

Based on rule 3, most chlorides are soluble, except for those of silver, lead, and mercury(I). Mercury(I) chloride is an exception, so it's insoluble.

Write the chemical formulas of the products and predict the precipitate

The products will be Mercury(I) chloride (Hg₂Cl₂) and acetic acid (HC₂H₃O₂). Hg₂Cl₂ is expected to be the precipitate. The precipitate formed is mercury(I) chloride (Hg₂Cl₂).

Key concepts

Precipitation Reactions

Precipitation reactions are a fascinating chemical process where two soluble salts react in aqueous solutions to form one or more insoluble products, known as precipitates. These reactions are fundamental to many natural and industrial processes. The principle behind precipitation is straightforward: when two ionic compounds are mixed in water, their ions may recombine to form a product that does not dissolve in water. This product settles out of the solution as a solid. To better grasp precipitation reactions, one must understand:

• Exchange of Ions: When solutions are mixed, the ions swap to potentially form new combinations.
• Insolubility: If a new combination of ions forms an insoluble compound, a precipitate occurs.
• Observation: A solid appears in what was originally a clear solution.

Applying these concepts, when copper(II) chloride (\( \mathrm{CuCl_2} \)) is mixed with ammonium sulfide (\( (\mathrm{NH_4})_2 \mathrm{S} \)), copper(II) sulfide (\( \mathrm{CuS} \)) forms as an insoluble precipitate.

Insoluble Compounds

Insoluble compounds are substances that do not dissolve in a solvent, most commonly water. In the context of precipitation reactions, knowing which compounds are insoluble helps predict the formation of a precipitate. The solubility rules give guidance on what ions typically form insoluble compounds. Here are some key insights:

• Common Insoluble Substances: Sulfides, phosphates, carbonates, and hydroxides often form insoluble compounds, with exceptions for compounds with alkali metals or ammonium.
• Specific Exceptions: For example, although many sulfides are insoluble, those containing alkali metals, ammonium, and certain transition metals like calcium remain soluble.
• Practical Examples: In a reaction of barium nitrate (\( \mathrm{Ba(NO_3)_2} \)) with potassium phosphate (\( \mathrm{K_3PO_4} \)), barium phosphate (\( \mathrm{Ba_3(PO_4)_2} \)) is insoluble and precipitates out of solution.

These rules and exceptions enable chemists to foresee which combinations are likely to yield insoluble products, hence, leading to precipitation.

Chemical Formula Writing

Writing chemical formulas correctly is a foundational skill in chemistry that allows for accurate representation and understanding of chemical reactions. When predicting precipitation reactions, the skill ensures you start with the correct reactants and predict the right products. Here's what you should keep in mind:

• Ion Charges: Understanding the typical charges of ions helps in writing correct formulas. For instance, copper typically forms a \(+2\) ion.
• Compound Formation: Combine ions in ratios that balance their overall charges to zero, such as \( \mathrm{CaCl_2} \) for calcium chloride.
• Practice: Regular practice of writing and balancing chemical equations is crucial. For example, combining silver acetate \( \mathrm{AgC_2H_3O_2} \) with calcium chloride \( \mathrm{CaCl_2} \) forms silver chloride \( \mathrm{AgCl} \) and calcium acetate \( \mathrm{Ca(C_2H_3O_2)_2} \).

By mastering chemical formula writing, a student can predict chemical reactions accurately and understand how different substances interact to form new products.