Problem 32 - Chemistry and Chemical Reactivity

Question

Balance the following reactions and then classify each as a precipitation, acid-base, or gas-forming reaction. Write the net ionic equation. (a) \(\mathrm{Fe}(\mathrm{OH})_{3}(\mathrm{s})+\mathrm{HNO}_{3}(\mathrm{aq}) \longrightarrow \mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{3}+\mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{FeCO}_{3}(\mathrm{s})+\mathrm{HNO}_{3}(\mathrm{aq}) \longrightarrow \mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}+\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

(a) Acid-base; Net ionic: \( \mathrm{Fe(OH)_3(s) + 3H^+(aq) \rightarrow \mathrm{Fe^{3+}(aq) + 3H_2O(l)}} \). (b) Gas-forming; Net ionic: \( \mathrm{FeCO_3(s) + 2H^+(aq) \rightarrow \mathrm{Fe^{2+}(aq) + CO_2(g) + H_2O(l)}} \).

Step 1: Analyze Reaction (a) - Unbalanced Equation

The unbalanced reaction given is \( \mathrm{Fe(OH)_3(s) + HNO_3(aq) \rightarrow \mathrm{Fe(NO_3)_3(aq) + H_2O(l)} \). This is a neutralization reaction between iron hydroxide and nitric acid.

Step 2: Balance Reaction (a) - Balancing Atoms

To balance the equation, balance the number of each type of atom on both sides of the reaction:1. Iron: 1 on each side.2. Nitrate: Add 3 \( \mathrm{HNO_3} \) to get 3 nitrate ions on the right.3. Balancing hydrogens: 3 molecules of \( \mathrm{HNO_3} \) provide 3 H to react with 3 OH from \( \mathrm{Fe(OH)_3} \) forming 3 water molecules.Balanced equation: \[ \mathrm{Fe(OH)_3(s) + 3HNO_3(aq) \rightarrow \mathrm{Fe(NO_3)_3(aq) + 3H_2O(l)}} \]

Step 3: Identify the Reaction Type (a)

This reaction is a neutralization (acid-base) reaction where an acid reacts with a base to form water and a salt.

Step 4: Write the Net Ionic Equation (a)

The net ionic equation is formed by removing spectator ions. As this is a neutralization reaction, we consider only these forms:\[ \mathrm{Fe(OH)_3(s) + 3H^+(aq) \rightarrow \mathrm{Fe^{3+}(aq) + 3H_2O(l)}} \]

Step 5: Analyze Reaction (b) - Unbalanced Equation

The unbalanced reaction given is \( \mathrm{FeCO_3(s) + HNO_3(aq) \rightarrow \mathrm{Fe(NO_3)_2(aq) + CO_2(g) + H_2O(l)} \). This involves the reaction of an acid with a carbonate, which is a typical gas-forming reaction.

Step 6: Balance Reaction (b) - Balancing Atoms

To balance the atoms in the equation:1. Carbon: 1 on each side.2. Iron: 1 on each side.3. Oxygen and Hidrogen: Add 2 \( \mathrm{HNO_3} \) to the reactants and equalize water molecules to balance hydrogen and oxygen.Balanced equation: \[ \mathrm{FeCO_3(s) + 2HNO_3(aq) \rightarrow \mathrm{Fe(NO_3)_2(aq) + CO_2(g) + H_2O(l)}} \]

Step 7: Identify the Reaction Type (b)

This reaction is a gas-forming reaction as it produces carbon dioxide gas when an acid reacts with a carbonate compound.

Step 8: Write the Net Ionic Equation (b)

To find the net ionic equation, remove the spectator ions:\[ \mathrm{FeCO_3(s) + 2H^+(aq) \rightarrow \mathrm{Fe^{2+}(aq) + CO_2(g) + H_2O(l)}} \]

Key Concepts

Reaction Balancing

When you're given a chemical reaction, you'll often need to ensure that it is balanced. Balancing a chemical reaction involves making sure that the number of atoms for each element is the same on both sides of the equation. This process follows the law of conservation of mass, which states that mass cannot be created or destroyed in a chemical reaction. To balance a reaction, you need to:

• Count the number of atoms for each element in the reactants and products.
• Add coefficients (numbers in front of the chemical formulas) to balance the number of atoms of each element on both sides of the equation.
• Never change the subscript numbers within a chemical formula to balance the equation.

For example, in Reaction (a) \[\mathrm{Fe(OH)_3(s) + HNO_3(aq) \rightarrow \mathrm{Fe(NO_3)_3(aq) + H_2O(l)}}\] you need to balance the nitrates and water by ensuring three molecules of nitric acid react with one molecule of iron hydroxide to form one molecule of iron(III) nitrate and three water molecules. Balanced chemical reactions are fundamental as they accurately depict the conservation of matter.

Net Ionic Equations

Once a chemical equation is balanced, you can write the net ionic equation. This type of equation only shows the chemical species that take part in the reaction, excluding spectator ions that do not participate. The goal is to simplify the chemical equation, highlighting the actual chemistry involved.To write a net ionic equation:

• Start with a balanced molecular equation.
• Separate the aqueous solutions into their respective ions (only strong electrolytes dissociate into ions).
• Identify and remove the spectator ions (ions that appear identical on both sides of the reaction).
• Write down what remains, ensuring all remaining components are balanced.

For Reaction (a), the net ionic equation is:\[\mathrm{Fe(OH)_3(s) + 3H^+(aq) \rightarrow \mathrm{Fe^{3+}(aq) + 3H_2O(l)}}\]This shows that iron(III) hydroxide reacts with hydrogen ions to form iron ions and water, without including the nitrate ions.

Acid-Base Reactions

Acid-base reactions are a key category in chemistry where an acid and a base react to neutralize each other, forming water and a salt. These reactions are fundamental because they occur frequently in chemistry and are essential for understanding how substances interact.In an acid-base reaction:

• The acid donates a proton (H⁺).
• The base provides a hydroxide ion (OH^-) or accepts a proton.
• Neutralization results in the formation of water and an ionic compound.

For Reaction (a), this is illustrated as:\[\mathrm{Fe(OH)_3(s) + 3HNO_3(aq) \rightarrow \mathrm{Fe(NO_3)_3(aq) + 3H_2O(l)}}\]The nitric acid donates protons to the iron hydroxide base, forming water. Knowledge of acid-base reactions helps predict product formation.

Gas-Forming Reactions

Gas-forming reactions are another type of chemical reaction where a gas is one of the products. These reactions usually occur when acids react with carbonates or bicarbonates to release carbon dioxide gas. Recognizing gas-forming reactions is important for understanding chemical processes and predicting physical changes like bubbling or effervescence in the solution.In these reactions:

• Acids react with carbonates or bicarbonates.
• Carbon dioxide gas and water are formed as typical products.
• These reactions often result in visible gas bubbles escaping from the solution.

For Reaction (b), the gas-forming reaction can be seen as:\[\mathrm{FeCO_3(s) + 2HNO_3(aq) \rightarrow \mathrm{Fe(NO_3)_2(aq) + CO_2(g) + H_2O(l)}}\]Carbonate reacts with nitric acid causing the release of CO₂. Such reactions are pivotal for processes like rock weathering and antacid function.