Problem 54 - Chemistry The Central Science In Si Units

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

For each part, write out the net ionic equation by identifying, balancing, and simplifying the redox reaction components.

Step 1: Identify the Reaction Components

For each subproblem, identify the reactants and products in the chemical reaction to understand the changes taking place. For example, in (a), the reactants are dilute nitric acid (\( \text{HNO}_3 \)) and zinc metal (\( \text{Zn} \)); the products include nitrous oxide (\( \text{N}_2\text{O} \)).

Step 2: Write the Molecular Equation

Write out the balanced molecular equation for each reaction. Taking (a) as an example, the molecular equation is: \[ 4 \text{HNO}_3 (aq) + \text{Zn}(s) \rightarrow \text{N}_2\text{O}(g) + 2 \text{H}_2\text{O}(l) + \text{Zn}^{2+}(aq) \].

Step 3: Separate into Ions: Ionic Equation

For each molecular equation, break down the soluble reactants and products into their ionic forms. For example, for (a): \[ 4 \text{H}^{+}(aq) + 4 \text{NO}_3^{-}(aq) + \text{Zn}(s) \rightarrow \text{N}_2\text{O}(g) + 2 \text{H}_2\text{O}(l) + \text{Zn}^{2+}(aq) \].

Step 4: Identify and Cancel Spectator Ions

Remove ions that appear unchanged on both sides of the ionic equation. In reaction (a), \( \text{NO}_3^{-} \) is cancelled out as it is a spectator ion.

Step 5: Write the Net Ionic Equation

For each reaction, write the balanced net ionic equation after removing the spectator ions. The net ionic equation for (a) is: \[ 4 \text{H}^{+}(aq) + \text{Zn}(s) \rightarrow \text{N}_2\text{O}(g) + 2 \text{H}_2\text{O}(l) + \text{Zn}^{2+}(aq) \].

Step 6: Apply Similar Steps to Remaining Reactions

Repeat Steps 1-5 for each of the other reactions, ensuring that each net ionic equation accurately reflects the overall change in oxidation states and mass balance.

Key Concepts

Balancing Chemical Equations

Balancing chemical equations is a critical aspect of chemistry, ensuring that the same number of each type of atom is present on both sides of the reaction. This reflects the fundamental conservation of mass, as matter cannot be created or destroyed.

To balance a chemical equation, start by writing the unbalanced equation that reflects the reactants and products. Then, count the number of atoms of each element on both sides. Adjust the coefficients (numbers in front of compounds or elements) to ensure that each element has the same number of atoms on each side of the equation.

Here are a few tips to help balance chemical equations easily:

• Begin by balancing elements that appear in only one reactant and one product.
• Balance polyatomic ions as a unit if they appear unchanged on both sides.
• Adjust coefficients progressively, reviewing one element at a time.
• Reassess all elements after balancing to confirm all atoms are balanced.

Effective balancing is essential for accurately representing chemical reactions and is the starting point for understanding reaction dynamics.

Oxidation-Reduction Reactions

Oxidation-reduction, or redox reactions, involve the transfer of electrons between substances. At their core, one substance is oxidized (loses electrons), and another is reduced (gains electrons).

To identify redox reactions, look for changes in oxidation states of elements from reactants to products. Remember these key points:

• The substance that loses electrons undergoes oxidation and its oxidation state increases.
• The substance that gains electrons undergoes reduction and its oxidation state decreases.
• Recognize agents in redox reactions: the oxidizing agent is the substance that gets reduced, while the reducing agent is the one that gets oxidized.

Redox reactions are fundamental in numerous natural processes and practical applications, such as metabolism, combustion, and corrosion. Understanding redox reactions helps in writing balanced net ionic equations by tracking electron movement, ensuring the same number of electrons are gained and lost throughout the reaction.

Chemical Reaction Writing

Chemical reaction writing involves creating symbolic representations of chemical processes. This includes writing molecular, ionic, and net ionic equations.

Here's how to approach writing chemical reactions:

• Molecular Equations: These show all reactants and products as if they were intact compounds. They provide an overview of the overall reaction.
• Ionic Equations: Break down soluble ionic compounds into their constituent ions. This emphasizes the ions that participate in the reaction, which could vary depending on the solution's phase or state.
• Net Ionic Equations: These strip away the spectator ions, showing only the chemical species that undergo a change. This helps in focusing on the actual chemical change occurring in the reaction.

Writing these equations correctly ensures an accurate depiction of the reaction dynamics and is a crucial step in understanding chemical processes, particularly when dealing with complex reactions, such as those involving metals and acids.