Problem 122 - Chemistry Matter and Change

Question

Apply Write the chemical equations and net ionic equations for each of the following reactions that might occur in aqueous solutions. If a reaction does not occur, write \(N R\) in place of the products. Magnesium phosphate precipitates in an aqueous solution. $$\begin{array}{l}{\text { a. } \mathrm{KNO}_{3}+\mathrm{CsCl} \rightarrow} \\\ {\text { b. } \mathrm{Ca}(\mathrm{OH})_{2}+\mathrm{KCN} \rightarrow} \\\ {\text { c. } \mathrm{Li}_{3} \mathrm{PO}_{4}+\mathrm{MgSO}_{4} \rightarrow} \\\ {\text { d. } \mathrm{HBrO}+\mathrm{NaOH} \rightarrow}\end{array}$$

Step-by-Step Solution

Answer

Reactions (a) and (b) are NR; (c) forms Mg\(_3\)(PO\(_4\))\(_2\); (d) NaBrO and H\(_2\)O form.

Step 1: Assess Reaction Type

We need to determine the types of reactions involved in each case to check if any chemical reaction will occur. For instance, we assess if they are double displacement, precipitation, or neutralization reactions.

Step 2: Write the Chemical Equations

For each given reaction, identify the possible products by swapping the anions between the cations and determining solubility using solubility rules.

Step 2a: Reaction (a)

Reactants: KNO\(_3\) and CsCl. Both products, KCl and CsNO\(_3\), are soluble in water, so no reaction occurs. \(\text{KNO}_3 + \text{CsCl} \rightarrow NR\).

Step 2b: Reaction (b)

Reactants: Ca(OH)\(_2\) and KCN. Both products, Ca(CN)\(_2\) and KOH, remain in aqueous solution, with no precipitate formed. So, no reaction occurs. \(\text{Ca(OH)}_2 + \text{KCN} \rightarrow NR\).

Step 2c: Reaction (c)

Reactants: Li\(_3\)PO\(_4\) and MgSO\(_4\). This is a potential precipitation reaction. Mg\(_3\)(PO\(_4\))\(_2\) is insoluble and will precipitate. \(\text{3 Li}_3\text{PO}_4(aq) + \text{3 MgSO}_4(aq) \rightarrow \text{Mg}_3(\text{PO}_4)_2(s) + \text{9 Li}_2\text{SO}_4(aq)\).

Step 3: Write the Net Ionic Equations

Now, isolate the ions involved in forming the precipitate for any reactions that occur and write the net ionic equation.

Step 3a: Reaction (a)

Since no reaction occurs, there is no net ionic equation. \(NR\).

Step 3b: Reaction (b)

Since no reaction occurs, there is no net ionic equation. \(NR\).

Step 3c: Reaction (c)

The ions that form the precipitate are 3Mg\(^{2+}\) and 2PO\(^{3-}_4\). The net ionic equation is \(3\text{Mg}^{2+}(aq) + 2\text{PO}_4^{3-}(aq) \rightarrow \text{Mg}_3(\text{PO}_4)_2(s)\).

Step 3d: Reaction (d)

Reactants: HBrO and NaOH. This is a neutralization reaction forming NaBrO (aq) and H\(_2\)O (l). \(\text{HBrO} + \text{NaOH} \rightarrow \text{NaBrO} + \text{H}_2\text{O}\). The net ionic equation is \(\text{HBrO} + \text{OH}^- \rightarrow \text{H}_2\text{O} + \text{BrO}^- \).

Key Concepts

Chemical Reactions

Chemical reactions are processes where substances, known as reactants, transform into different substances, called products. In chemistry, reactions can occur in various ways, such as through combination, decomposition, combustion, or displacement. Understanding the nature of the reaction is key to predicting the products formed.
In this exercise, you can often identify reaction types by looking at the reactants involved. Common types include:

• Double Displacement Reactions: This occurs when parts of two compounds are swapped to form new compounds, as evaluated in reactions (a) and (b).
• Precipitation Reactions: These occur when an insoluble solid, known as a precipitate, forms from the solution's anions and cations.
• Neutralization Reactions: These involve an acid and a base reacting to form water and salt, like in reaction (d).

Knowing the specific type of chemical reaction helps in finding the appropriate chemical and net ionic equations, much like a roadmap guiding you through the solution.

Aqueous Solutions

Aqueous solutions are solutions where water acts as the solvent. In these solutions, substances dissolve and often dissociate into ions, making the solution conductive to electricity. It's crucial for understanding reactions happening in water, especially those involving salts, acids, and bases.
For any given reaction, discerning whether a substance is dissolved in water (aqueous) or is in a different state (solid, liquid, gas) is crucial for predicting the outcome.
Important aspects of aqueous solutions include:

• Solubility: Determines whether a substance remains dissolved or precipitates. Using solubility rules helps predict reaction outcomes, as seen in reactions (a) and (b).
• Dissociation into Ions: In an aqueous solution, many compounds separate into ions. This is key for writing net ionic equations, which focus only on the ions that partake in forming products, especially precipitates.
• Conductivity: Solutions with ions conduct electricity. The more ions present, the higher the conductivity, influencing the nature of the reaction.

Precipitation Reactions

Precipitation reactions occur when two aqueous solutions combine to form an insoluble salt, known as a precipitate. This solid settles out of the solution, and its formation often signals that a chemical reaction has taken place.
To predict if a precipitation reaction will occur, apply solubility rules:

• Identify Ions in Solution: Look at the cations and anions present in the aqueous solutions.
• Check Solubility Rules: Solubility rules help ascertain whether the product of the reaction will remain dissolved or form a precipitate.

For instance, in reaction (c), mixing lithium phosphate and magnesium sulfate results in magnesium phosphate, a compound that is insoluble, hence it precipitates. This leads to the net ionic equation focusing on the formation of this solid: \[3\text{Mg}^{2+}(aq) + 2\text{PO}_4^{3-}(aq) \rightarrow \text{Mg}_3(\text{PO}_4)_2(s)\].

Neutralization Reactions

Neutralization reactions are a specific type of double displacement reaction where an acid reacts with a base to form water and a salt. These reactions are integral to many processes, from digestion to industrial chemical production.
In a neutralization reaction:

• The acid provides hydrogen ions ( H extsuperscript{+}) that combine with the base's hydroxide ions ( OH extsuperscript{-}) to form water.
• The remaining ions form a salt, typically soluble in water.

In the given exercise, reaction (d) between HBrO and NaOH exemplifies a neutralization process. The net ionic equation simplifies to:\[\text{HBrO} + \text{OH}^- \rightarrow \text{H}_2\text{O} + \text{BrO}^- \].
Understanding how to recognize and balance these reactions is crucial for mastering basic chemistry principles.