Problem 73 - Chemistry and Chemical Reactivity

Question

Write the net ionic equation and identify the spectator ion or ions in the reaction of nitric acid and magnesium hydroxide. What type of reaction is this? $$\begin{array}{r} 2 \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})+2 \mathrm{NO}_{3}^{-}(\mathrm{aq})+\mathrm{Mg}(\mathrm{OH})_{2}(\mathrm{s}) \rightarrow 4 \mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{Mg}^{2+}(\mathrm{aq})+2 \mathrm{NO}_{3}^{-}(\mathrm{aq}) \end{array}$$

Step-by-Step Solution

Answer

Net ionic equation: \[ 2 \text{H}_3\text{O}^+(\text{aq}) + \text{Mg(OH)}_2(\text{s}) \rightarrow 4 \text{H}_2\text{O}(\ell) + \text{Mg}^{2+}(\text{aq}) \] Spectator ion: \( \text{NO}_3^- \) Reaction type: Acid-base reaction.

Step 1: Write the Balanced Molecular Equation

The balanced equation for the reaction of nitric acid, which dissociates into hydronium ions \( \text{H}_3\text{O}^+ \) and nitrate ions \( \text{NO}_3^- \), with magnesium hydroxide \( \text{Mg(OH)}_2 \) is given as:\[ 2 \text{H}_3\text{O}^+(\text{aq}) + 2 \text{NO}_3^-(\text{aq}) + \text{Mg(OH)}_2(\text{s}) \rightarrow 4 \text{H}_2\text{O}(\ell) + \text{Mg}^{2+}(\text{aq}) + 2 \text{NO}_3^-(\text{aq}) \]

Step 2: Identify Aqueous Compounds and Break Them into Ions

We'll split the aqueous compounds into their ions, while leaving solids, liquids, and gases in their molecular form. The equation becomes:\[ 2 \text{H}_3\text{O}^+(\text{aq}) + 2 \text{NO}_3^-(\text{aq}) + \text{Mg(OH)}_2(\text{s}) \rightarrow 4 \text{H}_2\text{O}(\ell) + \text{Mg}^{2+}(\text{aq}) + 2 \text{NO}_3^-(\text{aq}) \]

Step 3: Cancel Spectator Ions

Spectator ions appear on both sides of the equation unchanged. In this reaction, \( \text{NO}_3^- \) ions are present on both sides, so they are the spectator ions. Cancel them out to simplify the equation.

Step 4: Write the Net Ionic Equation

After removing the spectator ions, the net ionic equation is left with just the ions that participate:\[ 2 \text{H}_3\text{O}^+(\text{aq}) + \text{Mg(OH)}_2(\text{s}) \rightarrow 4 \text{H}_2\text{O}(\ell) + \text{Mg}^{2+}(\text{aq}) \]

Step 5: Identify the Type of Reaction

This is an acid-base reaction, where the hydronium ions from nitric acid react with the hydroxide ions (from \( \text{Mg(OH)}_2 \)) to form water, and magnesium ions are dissolved.

Key Concepts

Spectator Ions

Spectator ions are ions that appear on both the reactant and product sides of a chemical reaction without undergoing any change themselves. They don't participate in the actual chemical reaction but are present in the solution to maintain electrical neutrality. In the given chemical reaction of nitric acid and magnesium hydroxide, the nitrate ions ( NO_3^- ) are the spectator ions. When writing a net ionic equation, spectator ions are removed, allowing you to focus on the ions and molecules that undergo change. Identifying and removing spectator ions helps to simplify chemical equations and highlights the actual chemical transformation occurring.

• Spectator ions do not affect the overall chemical process.
• They can be 'cancelled out' from both sides of the equation.
• Recognizing these ions can make balancing equations simpler.

Recognizing spectator ions is important in grasping essential reaction details and focusing on the chemistry that's truly happening.

Acid-Base Reactions

Acid-base reactions are a crucial aspect of chemistry, involving the transfer of protons (H+) between reactants. In the reaction you're examining, nitric acid acts as the acid and magnesium hydroxide as the base. This particular reaction takes place as follows: - Nitric acid provides the hydronium ions (H_3O^+).- These hydronium ions interact with the hydroxide ions from magnesium hydroxide to form water.The general form of an acid-base reaction is: \[ ext{Acid} + ext{Base} ightarrow ext{Water} + ext{Salt} \]In your exercise, the water is formed as a result of hydronium ions combining with the hydroxide ions. The remaining components form a salt, which is dissociating magnesium ions in this example. Such reactions are common and play a significant role in maintaining pH balance in various systems, including biological ones.

Chemical Reaction Types

Chemical reactions can be classified into different types based on their characteristics. Several major types include synthesis, decomposition, single replacement, double replacement, and combustion. The one demonstrated here, between nitric acid and magnesium hydroxide, is categorized as a double replacement and more specifically an acid-base reaction. To determine the type of reaction:

• Look at the reactants and products.
• Identify reactant and product composition changes.
• Observe the swapping of ions.

In acid-base reactions like this, the general principle involves proton donation and acceptance, resulting in the formation of water and a salt. By identifying the nature of reactants, such as acids and bases, one can use known reaction patterns to predict products and balance equations efficiently.