Problem 54 - Chemistry and Chemical Reactivity

Question

Balance the following equations, and then classify each as a precipitation, acid-base, or gas-forming reaction. Show states for the products (s, \(\ell, \mathrm{g},\) aq), and then balance the completed equation. Write the net ionic equation. (a) \(\mathrm{Fe}(\mathrm{OH})_{3}(\mathrm{s})+\mathrm{HNO}_{3}(\mathrm{aq}) \rightarrow \mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{3}+\mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{FeCO}_{3}(\mathrm{s})+\mathrm{HNO}_{3}(\mathrm{aq}) \rightarrow \mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}+\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

(a) is an acid-base reaction; (b) is a gas-forming reaction.

Step 1: Determine States for Products

Identify the states of the products based on their chemical nature. - For (a), Fe(NO₃)₃ is aqueous (aq) because it is a soluble salt, and H₂O is liquid (ℓ). - For (b), Fe(NO₃)₂ is aqueous (aq), CO₂ is a gas (g), and H₂O is liquid (ℓ).

Step 2: Balance the Equations

Balance each equation considering the conservation of mass. - For (a), Fe(OH)₃(s) + 3HNO₃(aq) → Fe(NO₃)₃(aq) + 3H₂O(ℓ) - For (b), FeCO₃(s) + 2HNO₃(aq) → Fe(NO₃)₂(aq) + CO₂(g) + H₂O(ℓ)

Step 3: Classify the Reaction

Classify each reaction based on the products formed. - (a) is an acid-base reaction: Fe(OH)₃ reacts with HNO₃ to form Fe(NO₃)₃ and water. - (b) is a gas-forming reaction: FeCO₃ reacts with HNO₃ to form CO₂ gas.

Step 4: Write the Full Ionic Equation

Convert balanced molecular equations to full ionic equations by dissociating all aqueous compounds into their respective ions. - (a) Fe(OH)₃(s) + 3H⁺(aq) + 3NO₃⁻(aq) → Fe³⁺(aq) + 3NO₃⁻(aq) + 3H₂O(ℓ) - (b) FeCO₃(s) + 2H⁺(aq) + 2NO₃⁻(aq) → Fe²⁺(aq) + 2NO₃⁻(aq) + CO₂(g) + H₂O(ℓ)

Step 5: Write the Net Ionic Equation

Simplify by canceling out spectator ions to find the net ionic equation. Spectator ions do not participate in the reaction itself. - (a) Fe(OH)₃(s) + 3H⁺(aq) → Fe³⁺(aq) + 3H₂O(ℓ) - (b) FeCO₃(s) + 2H⁺(aq) → Fe²⁺(aq) + CO₂(g) + H₂O(ℓ)

Key Concepts

Acid-Base Reactions

Acid-base reactions are fundamental chemical processes in which an acid reacts with a base, typically producing water and a salt. A classic example of this type of reaction is the neutralization of acids by bases.
In the reaction provided, Fe(OH)₃, which is a base, reacts with HNO₃, an acid. During this reaction, a salt, Fe(NO₃)₃, and water, H₂O, are formed:

• Reactants: Fe(OH)₃(s) + 3HNO₃(aq)
• Products: Fe(NO₃)₃(aq) + 3H₂O(ℓ)

Here, Fe(OH)₃, a solid, dissolves by reacting with HNO₃, leading to the formation of Fe³⁺ ions in solution, water (liquid), and NO₃⁻ ions. This change represents a dynamic shift from solid to liquid and aqueous states, exemplifying the transformation typical in acid-base reactions.

Gas-Forming Reactions

Gas-forming reactions are another important concept to understand in the realm of chemical reactions. These involve a chemical reaction where a gas is formed as one of the products. These reactions often occur when carbonates react with acids.
In the example reaction FeCO₃(s) + 2HNO₃(aq) → Fe(NO₃)₂(aq) + CO₂(g) + H₂O(ℓ), we observe:

• FeCO₃, a carbonate compound, reacts with nitric acid, HNO₃.
• One of the key products is carbon dioxide gas (CO₂), which is easily identifiable as it escapes as bubbles during the reaction.

The presence of CO₂ signifies that a gas is forming in the reaction, classifying it as a gas-forming reaction. This type is very common when carbonates and bicarbonates come into contact with acids.

Net Ionic Equations

Net ionic equations provide a simplified way to represent reactions by only focusing on the components that undergo a chemical change. To achieve this, one must remove the spectator ions—ions that appear unchanged on both the reactant and product sides.
For example, in the given reactions:

• The full ionic equation for reaction (a) includes spectator ions: Fe(OH)₃(s) + 3H⁺(aq) + 3NO₃⁻(aq) → Fe³⁺(aq) + 3NO₃⁻(aq) + 3H₂O(ℓ)
• By removing the NO₃⁻, which remains unchanged, the net ionic equation becomes: Fe(OH)₃(s) + 3H⁺(aq) → Fe³⁺(aq) + 3H₂O(ℓ)

The simplification helps highlight the essence of the chemical change. Similarly, grasping the net ionic equation for gas-forming reactions aids in quickly identifying the participating ions and molecules, making complex reactions easier to understand.

States of Matter in Reactions

Understanding the states of matter in a reaction is essential, as it provides crucial insight into the physical changes that accompany a chemical process. These states include solid (s), liquid (ℓ), gas (g), and aqueous (aq)—where aqueous refers to a substance dissolved in water.
In the given reactions:

• The reactants Fe(OH)₃ and FeCO₃ are initially in solid (s) state.
• HNO₃ is in aqueous (aq) solution, indicating it's dissolved in water.
• Reaction products like H₂O appear as a liquid (ℓ), and CO₂ is released as a gas (g).

Recognizing these states can help predict the behavior of substances during the reaction, such as precipitation formation, gas evolution, or solid dissolution. By understanding the implications of each state, students can better visualize and anticipate the outcome of the reaction.