Question

Complete and balance each of the following molecular equations, including phase labels, if a reaction occurs. Then write the net ionic equation. If no reaction occurs, write \(N R\) after the arrow. (a) \(\mathrm{Sr}(\mathrm{OH})_{2}+\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2} \longrightarrow\) (b) \(\mathrm{NH}_{4} \mathrm{I}+\mathrm{CsCl} \longrightarrow\) (c) \(\mathrm{NaNO}_{3}+\mathrm{CsCl} \longrightarrow\) (d) \(\mathrm{NH}_{4} \mathrm{I}+\mathrm{AgNO}_{3} \longrightarrow\)

Short answer

(a) produces Sr(C2H3O2)2 and water; net ionic: OH⁻ + H⁺ → H2O. (b) and (c) have no reactions. (d) forms AgI; net ionic: Ag⁺ + I⁻ → AgI.

Step-by-step solution

Identify Types of Reactions

First, identify the types of chemical reactions by examining reactants: - (a) is a neutralization reaction between a base (Sr(OH)₂) and an acid (HC₂H₃O₂). - (b) may involve a possible double displacement between two ionic compounds. - (c) also suggests a double displacement between ionic compounds. - (d) indicates a possible precipitation reaction between NH₄I and AgNO₃.

Molecular Equation for Reaction (a)

Write the molecular equation for the neutralization reaction:\[\text{Sr(OH)}_2(aq) + 2 \text{HC}_2\text{H}_3\text{O}_2(aq) \rightarrow \text{Sr(C}_2\text{H}_3\text{O}_2)_2(aq) + 2 \text{H}_2\text{O}(l)\]

Net Ionic Equation for Reaction (a)

Identify and cancel the spectator ions to write the net ionic equation for reaction (a):\[\text{OH}^-(aq) + \text{H}^+(aq) \rightarrow \text{H}_2\text{O}(l)\]

Molecular Equation for Reaction (b)

Determine the products of the possible double displacement reaction:\[\text{NH}_4\text{I}(aq) + \text{CsCl}(aq) \rightarrow \text{NR}\]No precipitation occurs as all compounds are soluble.

Molecular Equation for Reaction (c)

Write the molecular equation for reaction (c):\[\text{NaNO}_3(aq) + \text{CsCl}(aq) \rightarrow \text{NR}\]No new insoluble products are formed, indicating no reaction occurs.

Molecular Equation for Reaction (d)

Predict the double displacement products:\[\text{NH}_4\text{I}(aq) + \text{AgNO}_3(aq) \rightarrow \text{AgI}(s) + \text{NH}_4\text{NO}_3(aq)\]

Net Ionic Equation for Reaction (d)

Write the net ionic equation for reaction (d), where the precipitate is formed:\[\text{Ag}^+(aq) + \text{I}^-(aq) \rightarrow \text{AgI}(s)\]

Key concepts

Net Ionic Equations

Net ionic equations simplify chemical equations by showing only the species that are involved in the actual chemical change. In these equations, spectator ions, which do not participate directly in the reaction, are left out. This makes it easier to understand what happens during a chemical process.

For example, in a reaction involving an acid and a base like Sr(OH)₂ and HC₂H₃O₂, we begin with the molecular equation and then identify spectator ions. In this neutralization reaction, the relevant part is the formation of water, H₂O, from hydroxide (OH⁻) ions and hydrogen ions (H⁺). By canceling out the other ions that do not play a role in this transition, we are left with the equation:

• OH⁻(aq) + H⁺(aq) → H₂O(l)

This is the net ionic equation and it succinctly captures the essence of the reaction.

Neutralization Reactions

Neutralization reactions involve an acid and a base reacting to form water and a salt. They are a subset of double displacement reactions and are most commonly seen with acids like hydrochloric acid (HCl) or acetic acid (HC₂H₃O₂) reacting with bases like sodium hydroxide (NaOH) or strontium hydroxide (Sr(OH)₂).

The reaction of Sr(OH)₂ with HC₂H₃O₂ is a prime example. The balanced molecular equation first identifies that for each strontium hydroxide molecule, two acetic acid molecules are needed to fully neutralize the hydroxide ions:

• Sr(OH)₂(aq) + 2 HC₂H₃O₂(aq) → Sr(C₂H₃O₂)₂(aq) + 2 H₂O(l)

This reaction is key in understanding how acids and bases interact, leading to the formation of water and a dissolved ionic salt.

Double Displacement Reactions

Double displacement reactions, sometimes called double replacement reactions, occur when parts of two ionic compounds are exchanged and form two new compounds. A characteristic feature of these reactions is the swapping of ions between the reacting compounds.

A perfect case is when discussing reaction (b) and (d) in the exercise. In reaction (b) with NH₄I and CsCl, no reaction occurs despite the potential double displacement setup. This means that no new compounds form that are less soluble than the reactants. However, reaction (d) featuring NH₄I with AgNO₃ leads to the formation of a precipitate, AgI:

• NH₄I(aq) + AgNO₃(aq) → AgI(s) + NH₄NO₃(aq)

These reactions highlight how solubility rules are crucial in predicting the occurrence of such reactions.

Precipitation Reactions

Precipitation reactions occur when two aqueous solutions react to form an insoluble substance, called a precipitate. This type of reaction is another common example of double displacement reactions.

In the case of reaction (d), we have NH₄I and AgNO₃ reacting to form AgI, a yellow solid precipitate. This formation of AgI can be predicted knowing the low solubility of silver iodide in water. The equation captures this effect:

• Ag⁺(aq) + I⁻(aq) → AgI(s)

Precipitation reactions are important in many fields, including analytical chemistry, where they help in determining the presence of certain ions in solution. Understanding this allows you to anticipate whether a visual change will occur, and if so, it signifies the formation of an insoluble product.