Problem 54 - Chemistry: The Central Science in SI Units, Global Edition

Question

Write a balanced net ionic equation for each of the following reactions: (a) Dilute nitric acid reacts with zinc metal with formation of nitrous oxide. (b) Concentrated nitric acid reacts with sulfur with formation of nitrogen dioxide. (c) Concentrated nitric acid oxidizes sulfur dioxide with formation of nitric oxide. (d) Hydrazine is burned in excess fluorine gas, forming \(\mathrm{NF}_{3}\). (e) Hydrazine reduces \(\mathrm{CrO}_{4}^{2-}\) to \(\mathrm{Cr}(\mathrm{OH})_{4}^{-}\) in base (hydrazine is oxidized to \(\mathrm{N}_{2}\) ).

Step-by-Step Solution

Answer

\(a) Zn + 10H^+ \rightarrow 2Zn^{2+} + N_2O + 6H_2O\) \(b) S + 2H^+ \rightarrow SO_4^{2-} + 6NO_2\) \(c) 2SO_2 \rightarrow 4NO + 2SO_4^{2-}\) \(d) N_2H_4 + 3F_2 \rightarrow 4NF_3\) \(e) N_2H_4 + CrO_4^{2-} + 4H_2O \rightarrow N_2 + Cr(OH)_4^-\)

Step 1: Write the unbalanced chemical equation

Identify the reactants and products of the reaction: Zn + HNO3 -> Zn(NO3)2 + N2O + H2O

Step 2: Balance the chemical equation

Balance the equation by adjusting the coefficients of the reactants and products: 2Zn + 5HNO3 -> 2Zn(NO3)2 + N2O + 3H2O

Step 3: Write the net ionic equation

Break down the ionic compounds and eliminate spectator ions (NO₃⁻): Zn + 10H⁺ + 6NO₃⁻ -> 2Zn²⁺ + 12NO₃⁻ + N₂O + 6H₂O The net ionic equation will be: Zn + 10H⁺ -> 2Zn²⁺ + N₂O + 6H₂O ---------------------------------------------------------------- #b) Concentrated nitric acid reacts with sulfur#

Step 1: Write the unbalanced chemical equation

Identify the reactants and products of the reaction: S + HNO3 -> H2SO4 + NO2

Step 2: Balance the chemical equation

Balance the equation by adjusting the coefficients of the reactants and products: S + 6HNO3 -> H2SO4 + 6NO2

Step 3: Write the net ionic equation

Break down the ionic compounds and eliminate spectator ions (NO₃⁻): S + 6H⁺ + 6NO₃⁻ -> 2H⁺ + SO₄²⁻ + 6NO₂ The net ionic equation will be: S + 6H⁺ -> SO₄²⁻ + 6NO2 + 4H⁺ Simplifying, we have: S + 2H⁺ -> SO₄²⁻ + 6NO₂ ---------------------------------------------------------------- #c) Concentrated nitric acid oxidizes sulfur dioxide#

Step 1: Write the unbalanced chemical equation

Identify the reactants and products of the reaction: SO2 + HNO3 -> NO + H2SO4

Step 2: Balance the chemical equation

Balance the equation by adjusting the coefficients of the reactants and products: 2SO2 + 4HNO3 -> 4NO + 2H2SO4

Step 3: Write the net ionic equation

Break down the ionic compounds and eliminate the spectator ions (NO₃⁻): 2SO₂ + 4H⁺ + 4NO₃⁻-> 4NO + 4H⁺ + 2SO₄²⁻ The net ionic equation will be: 2SO₂ -> 4NO + 2SO₄²⁻ ---------------------------------------------------------------- #d) Hydrazine is burned in excess fluorine gas#

Step 1: Write the unbalanced chemical equation

Identify the reactants and products of the reaction: N2H4 + F2 -> NF3

Step 2: Balance the chemical equation

Balance the equation by adjusting the coefficients of the reactants and products: N2H4 + 3F2 -> 4NF3

Step 3: Write the net ionic equation

There are no ionic compounds in this reaction, so the net ionic equation is the same as the balanced chemical equation: N2H4 + 3F2 -> 4NF3 ---------------------------------------------------------------- #e) Hydrazine reduces CrO4 2- in base#

Step 1: Write the unbalanced chemical equation

Identify the reactants and products of the reaction: N2H4 + CrO4 2- -> N2 + Cr(OH)4^-

Step 2: Balance the chemical equation

Balance the equation by adjusting the coefficients of the reactants and products (balance the oxygens using water molecules): N2H4 + CrO4 2- + 4H2O -> N2 + Cr(OH)4^-

Step 3: Write the net ionic equation

The net ionic equation will be: N2H4 + CrO₄²⁻ + 4H2O -> N2 + Cr(OH)₄⁻

Key Concepts

Understanding Chemical Reactions

Chemical reactions are processes where reactants transform into one or more new products. These transformations involve breaking bonds in reactants and forming new bonds in products.
The process can be represented by a chemical equation, which not only shows substances involved but also their coefficients.

• Reactants are on the left side.
• Products are on the right side.

For example, in the reaction of zinc with nitric acid: Zn + HNO₃ → Zn(NO₃)₂ + N₂O + H₂O.
Understanding what happens in a reaction helps us predict product formation and understand the reaction mechanism.

Balancing Chemical Equations

Balancing chemical equations is a crucial step in understanding chemical reactions. A balanced equation has equal numbers of each type of atom on both sides. This ensures the law of conservation of mass is followed.
To balance a chemical equation:

• Write the unbalanced equation.
• Adjust coefficients to have the same number of each atom on both sides.

For instance, consider the unbalanced equation used earlier: Zn + HNO₃ → Zn(NO₃)₂ + N₂O + H₂O. We balance each atom, resulting in: 2Zn + 5HNO₃ → 2Zn(NO₃)₂ + N₂O + 3H₂O.
Balancing equations helps predict the amount of reactants needed or products formed.

Oxidation-Reduction Reactions

Oxidation-reduction reactions, or redox reactions, are processes where electrons are transferred between substances. These reactions consist of two parts: oxidation, where a substance loses electrons, and reduction, where a substance gains electrons.
Consider this in the context of hydrazine reducing chromate ( CrO₄^{2-} ). Here, hydrazine ( N_{2}H_{4} ) is oxidized to nitrogen ( N_{2} ), and chromate is reduced to Cr(OH)₄⁻.

• The oxidizing agent is the substance that gets reduced.
• The reducing agent is the substance that gets oxidized.

Net ionic equations provide a clear picture of redox processes by showing only those entities that participate in the electron transfer.