Problem 99 - Chemistry Matter and Change

Question

Write complete ionic and net ionic equations for each of the following reactions. a. \(\mathrm{K}_{2} \mathrm{S}(\mathrm{aq})+\mathrm{CoCl}_{2}(\mathrm{aq}) \rightarrow 2 \mathrm{KCl}(\mathrm{aq})+\mathrm{CoS}(\mathrm{s})\) b. \(\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq})+\mathrm{CaCO}_{3}(\mathrm{s}) \rightarrow\) \(\mathrm{H}_{2} \mathrm{O}(1)+\mathrm{CO}_{2}(\mathrm{g})+\mathrm{CaSO}_{4}(\mathrm{s})\) c. \(2 \mathrm{HClO}(\mathrm{aq})+\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq}) \rightarrow_{2 \mathrm{H}_{2} \mathrm{O}(1)+\mathrm{Ca}(\mathrm{ClO})_{2}(\mathrm{aq})}\)

Step-by-Step Solution

Answer

The short answer for the net ionic equations: a) \(S^{2-}(aq) + Co^{2+}(aq) \rightarrow CoS(s)\) b) \(2H^+(aq) + SO_4^{2-}(aq) + CaCO_3(s) \rightarrow H_2O(l) + CO_2(g) + CaSO_4(s)\) (no spectator ions) c) \(2H^+(aq) + 2OH^-(aq) \rightarrow 2H_2O(l)\)

Step 1: Write complete ionic equation

Split all aqueous substances into their constituent ions: \[2K^+(aq) + S^{2-}(aq) + Co^{2+}(aq) + 2Cl^-(aq) \rightarrow 2K^+(aq) + 2Cl^-(aq) + CoS(s)\]

Step 2: Write net ionic equation

Cancel out spectator ions and write the net ionic equation: \[S^{2-}(aq) + Co^{2+}(aq) \rightarrow CoS(s)\] For reaction (b) \(\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq})+\mathrm{CaCO}_{3}(\mathrm{s}) \rightarrow \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{CO}_{2}(\mathrm{g})+\mathrm{CaSO}_{4}(\mathrm{s})\)

Step 1: Write complete ionic equation

Split all aqueous substances into their constituent ions: Note that solids, liquids, and gases do not dissociate and are not split into ions. \[2H^+(aq) + SO_4^{2-}(aq) + CaCO_3(s) \rightarrow H_2O(l) + CO_2(g) + CaSO_4(s)\]

Step 2: Write net ionic equation

Cancel out spectator ions and write the net ionic equation: \[2H^+(aq) + SO_4^{2-}(aq) + CaCO_3(s) \rightarrow H_2O(l) + CO_2(g) + CaSO_4(s)\] In this case, there are no spectator ions, so the complete ionic equation is the same as the net ionic equation. For reaction (c) \(2 \mathrm{HClO}(\mathrm{aq})+\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq}) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{Ca}(\mathrm{ClO})_{2}(\mathrm{aq})\)

Step 1: Write complete ionic equation

Split all aqueous substances into their constituent ions: \[2H^+(aq) + 2ClO^-(aq) + Ca^{2+}(aq) + 2OH^-(aq) \rightarrow 2H_2O(l) + Ca^{2+}(aq) + 2ClO^-(aq)\]

Step 2: Write net ionic equation

Cancel out spectator ions and write the net ionic equation: \[2H^+(aq) + 2OH^-(aq) \rightarrow 2H_2O(l)\]

Key Concepts

Complete Ionic Equation

When a chemical reaction occurs in aqueous solution, compounds that dissolve in water split into ions. These are represented in complete ionic equations. The purpose of a complete ionic equation is to show all the ions in a solution before they react.
To write a complete ionic equation, follow these basic steps:

• Identify and separate all compounds in a reaction that dissolve in water, i.e., the aqueous compounds.
• Write each of these as individual ions, clearly showing their charges and physical states.
• Leave the substances that do not dissolve in water, such as solids, liquids, and gases, in their molecular form.

This way, you can clearly see all entities involved in the reaction, making it easier to identify which ions participate directly in the chemical transformation.

Net Ionic Equation

A net ionic equation zooms in on the essence of a chemical reaction by focusing only on the components that directly participate in the chemical change. This means it excludes the spectator ions that do not participate in the reaction.
To derive a net ionic equation, you should:

• Start with the complete ionic equation and observe which ions appear unchanged on both sides of the equation.
• Eliminate these spectator ions to simplify the equation.
• What remains will be the net ionic equation, showing only the ions that form the new compound or participate in the reaction itself.

This stripped-down version of the reaction is crucial for understanding the specific chemical changes, helping students focus on the actual transformation occurring.

Chemical Reactions

Chemical reactions involve the rearrangement of atoms to transform substances. In chemistry, reactions are usually represented by chemical equations that depict the conversion of reactants into products. Understanding these equations is essential to predict the products and the behavior of substances in a reaction.
In the context of aqueous reactions, it is important to be aware of what substances dissolve in water, which may affect how the reaction proceeds. Some reactions can have precipitates; others can produce gases or remain completely in solution.
Everything from identifying reactants and products to writing and balancing chemical equations forms fundamental skills in chemistry that allow students to predict reaction mechanisms effectively.

Spectator Ions

Spectator ions are ever-present in a chemical reaction but do not chemically change during the reaction process. They exist in the same state among the reactants and products. Essentially, they "watch" the reaction but don't participate.
To identify whether an ion is a spectator ion:

• Look for ions that appear identically on both sides of a complete ionic equation.
• These ions often stay dissolved in the solution and do not contribute to the formation of a precipitate or a new product.
• Understanding which ions are spectators helps in simplifying chemical equations to their net ionic forms.

Recognizing spectator ions is crucial for focusing on the true changes happening in the reaction and for understanding the chemistry behind the equations.