Problem 99 - Chemistry Matter and Change

Question

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

Step-by-Step Solution

Answer

Net ionic equations: (a) \( \mathrm{S}^{2-}(\mathrm{aq}) + \mathrm{Co}^{2+}(\mathrm{aq}) \rightarrow \mathrm{CoS}(\mathrm{s}) \); (b) \( 2\mathrm{H}^+(\mathrm{aq}) + \mathrm{CaCO}_{3}(\mathrm{s}) \rightarrow \mathrm{H}_{2} \mathrm{O}(1) + \mathrm{CO}_{2}(\mathrm{g}) + \mathrm{CaSO}_{4}(\mathrm{s}) \); (c) \( 2\mathrm{HClO}(\mathrm{aq}) + 2\mathrm{OH}^-(\mathrm{aq}) \rightarrow 2\mathrm{H}_2\mathrm{O}(1) + 2\mathrm{ClO}^-(\mathrm{aq}) \).

Step 1: Identify the Dissolved Ionic Compounds

For each reaction, identify which compounds are dissolved in water (aqueous, \(aq\)), since these will dissociate into their ions.

Step 2: Write the Complete Ionic Equation for Reaction (a)

For the reaction \( \mathrm{K}_{2} \mathrm{S}(\mathrm{aq})+\mathrm{CoCl}_{2}(\mathrm{aq}) \rightarrow 2 \mathrm{KCl}(\mathrm{aq})+\mathrm{CoS}(\mathrm{s}) \), break down the aqueous compounds into ions. This yields:\[2\mathrm{K}^+(\mathrm{aq}) + \mathrm{S}^{2-}(\mathrm{aq}) + \mathrm{Co}^{2+}(\mathrm{aq}) + 2 \mathrm{Cl}^-(\mathrm{aq}) \rightarrow 2\mathrm{K}^+(\mathrm{aq}) + 2 \mathrm{Cl}^-(\mathrm{aq}) + \mathrm{CoS}(\mathrm{s})\]

Step 3: Write the Net Ionic Equation for Reaction (a)

Cancel out spectator ions (ions that appear on both sides of the equation), which are \(\mathrm{K}^+\) and \(\mathrm{Cl}^-\). The net ionic equation is:\[\mathrm{S}^{2-}(\mathrm{aq}) + \mathrm{Co}^{2+}(\mathrm{aq}) \rightarrow \mathrm{CoS}(\mathrm{s})\]

Step 4: Write the Complete Ionic Equation for Reaction (b)

For the reaction \( \mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq})+\mathrm{CaCO}_{3}(\mathrm{s}) \rightarrow \mathrm{H}_{2} \mathrm{O}(1)+\mathrm{CO}_{2}(\mathrm{g})+\mathrm{CaSO}_{4}(\mathrm{s}) \), only \(\mathrm{H}_2\mathrm{SO}_4\) is in aqueous form and dissociates:\[2\mathrm{H}^+(\mathrm{aq}) + \mathrm{SO}_4^{2-}(\mathrm{aq}) + \mathrm{CaCO}_{3}(\mathrm{s}) \rightarrow \mathrm{H}_{2} \mathrm{O}(1) + \mathrm{CO}_{2}(\mathrm{g}) + \mathrm{CaSO}_{4}(\mathrm{s})\]

Step 5: Write the Net Ionic Equation for Reaction (b)

Since \(\mathrm{CaCO}_3\), \(\mathrm{H_2O}\), \(\mathrm{CO_2}\), and \(\mathrm{CaSO}_4\) do not dissociate into ions, the equation remains the same without spectator ions:\[2\mathrm{H}^+(\mathrm{aq}) + \mathrm{CaCO}_{3}(\mathrm{s}) \rightarrow \mathrm{H}_{2} \mathrm{O}(1) + \mathrm{CO}_{2}(\mathrm{g}) + \mathrm{CaSO}_{4}(\mathrm{s})\]

Step 6: Write the Complete Ionic Equation for Reaction (c)

For \( 2\mathrm{HClO}(\mathrm{aq})+\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq}) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(1)+\mathrm{Ca}(\mathrm{ClO})_{2}(\mathrm{aq}) \), both reactants and \(\mathrm{Ca}(\mathrm{ClO})_{2}\) are aqueous and dissociate:\[2\mathrm{HClO}(\mathrm{aq}) + \mathrm{Ca}^{2+}(\mathrm{aq}) + 2\mathrm{OH}^-(\mathrm{aq}) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(1) + \mathrm{Ca}^{2+}(\mathrm{aq}) + 2\mathrm{ClO}^-(\mathrm{aq})\]

Step 7: Write the Net Ionic Equation for Reaction (c)

Remove the spectator ions, which are \(\mathrm{Ca}^{2+}\). The net ionic equation is:\[2\mathrm{HClO}(\mathrm{aq}) + 2\mathrm{OH}^-(\mathrm{aq}) \rightarrow 2\mathrm{H}_2\mathrm{O}(1) + 2\mathrm{ClO}^-(\mathrm{aq})\]

Key Concepts

Net Ionic Equations

A net ionic equation is a simplified version of a full chemical equation. It shows only the particles that take part in the reaction. Imagine you have a huge party and only invite the people who'll join in the games, that's a bit like net ionic equations!

In any chemical reaction, some compounds disassociate into their constituent ions when dissolved in water. A net ionic equation focuses solely on these active participants, ignoring the ones that do not change during the reaction, known as spectator ions.

• For example, consider the reaction of potassium sulfide (\( \mathrm{K}_2\mathrm{S} \)) and cobalt chloride (\( \mathrm{CoCl}_2 \)). The net ionic equation focuses only on \( \mathrm{S}^{2-} \) and \( \mathrm{Co}^{2+} \) forming solid cobalt sulfide (\( \mathrm{CoS} \)).
• This is helpful for highlighting how substances react, providing insight into what forms the final product.

Spectator Ions

Spectator ions are like the people at a party who are just there to watch, they don't actively participate in the process. In chemical reactions occurring in aqueous solutions, these ions appear on both the reactant and product sides of the equation without changing.

• For example, in the reaction of \( \mathrm{K}_{2}\mathrm{S} \) and \( \mathrm{CoCl}_2 \), the potassium \( \mathrm{K}^+ \) and chloride \( \mathrm{Cl}^- \) ions are spectator ions. They are present but do not take part in forming the product, \( \mathrm{CoS} \).
• Identifying spectator ions is crucial as it helps in reducing a complete ionic equation into a net ionic equation, simplifying the analysis of the reaction.

Spectator ions maintain neutrality in charge throughout the chemical reaction, and though they don't partake in the formation of products, they provide a balanced medium for the reaction to occur.

Aqueous Solutions

Aqueous solutions are a type of chemical system where water acts as the solvent. When substances dissolve in water, they often separate into ions, making the solution able to conduct electricity.

• In reactions, we add the '(aq)' symbol to label substances that dissolve in water. This denotes that they exist as ions in solution.
• For instance, when \( \mathrm{H}_{2} \mathrm{SO}_{4} \) is in an aqueous solution, it dissociates into \( \mathrm{H}^+ \) and \( \mathrm{SO}_{4}^{2-} \) ions.

Aqueous solutions are crucial due to their properties. They facilitate the movement of ions and allow for reactions to occur more rapidly and efficiently. This makes them integral to many processes in both domestic and industrial chemistry.

Chemical Reactions

Chemical reactions are processes where substances change into new substances. They occur all around us, even within our bodies!

• They involve the breaking and forming of bonds, which transforms reactants into products.
• Take for instance, the reaction \(\mathrm{H}_{2}\mathrm{SO}_{4} + \mathrm{CaCO}_{3} \). Here, the acid-base reaction results in the formation of water, carbon dioxide, and calcium sulfate.

In chemical reactions, the law of conservation of mass holds, which means atoms are neither created nor destroyed. It's important to write and balance chemical equations to ensure this principle is maintained, reminding us of the constancy of substance in the universe.