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Chapter 17: Problem 65

Hydrazine is somewhat toxic. Use the half-reactions shown below to explain why household bleach (a highly alkaline solution of sodium hypochlorite) should not be mixed with household ammonia or glass cleansers that contain ammonia. $$\begin{array}{c} \mathrm{ClO}^{-}+\mathrm{H}_{2} \mathrm{O}+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{OH}^{-}+\mathrm{Cl}^{-} \quad \quad \quad \mathscr{E}^{\circ}=0.90 \mathrm{V} \\ \mathrm{N}_{2} \mathrm{H}_{4}+2 \mathrm{H}_{2} \mathrm{O}+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{NH}_{3}+2 \mathrm{OH}^{-} \quad \mathscr{E}^{\circ}=-0.10 \mathrm{V} \end{array}$$

Short Answer

Expert verified
When household bleach (containing ClO⁻) is mixed with ammonia (NH₃) or cleansers containing ammonia, the reaction leads to the formation of toxic hydrazine (N₂H₄) in an alkaline environment: \[ \mathrm{ClO}^{-}+\mathrm{N}_{2} \mathrm{H}_{4}+2 \mathrm{H}_{2} \mathrm{O} \longrightarrow\mathrm{Cl}^{-}+2 \mathrm{NH}_{3}+4 \mathrm{OH}^{-} \] Hence, mixing bleach with ammonia-containing substances is hazardous and should be avoided.

Step by step solution

01

Balancing the electron transfer

Since the number of electrons in both half-reactions is equal (2), the reactions can be added directly without the need to multiply these reactions based on the least common multiple.
02

Combining the half-reactions

Combine the given half-reactions by adding them. Remember that the electrons will cancel each other out when combining them: \[\mathrm{ClO}^{-}+\mathrm{H}_{2} \mathrm{O}+2 \mathrm{e}^{-} \longrightarrow 2\mathrm{OH}^{-}+\mathrm{Cl}^{-}\] \[\mathrm{N}_{2} \mathrm{H}_{4}+2 \mathrm{H}_{2} \mathrm{O}+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{NH}_{3}+2 \mathrm{OH}^{-}\] Adding them together, we get: \[\mathrm{ClO}^{-}+\mathrm{N}_{2} \mathrm{H}_{4}+4 \mathrm{H}_{2} \mathrm{O} \longrightarrow 2\mathrm{OH}^{-}+\mathrm{Cl}^{-}+2 \mathrm{NH}_{3}+2 \mathrm{OH}^{-}\]
03

Simplifying the reaction

Now we can simplify the resulting equation by canceling out equal components on both sides of the reaction: \[\mathrm{ClO}^{-}+\mathrm{N}_{2} \mathrm{H}_{4}+2 \mathrm{H}_{2} \mathrm{O} \longrightarrow\mathrm{Cl}^{-}+2 \mathrm{NH}_{3}+4 \mathrm{OH}^{-}\]
04

Analyzing the products

In simpler terms, when household bleach (containing ClO⁻) is mixed with ammonia (NH₃) or cleansers containing ammonia, the reaction produces chloride ions (Cl⁻), ammonia (NH₃), and hydroxide ions (OH⁻): \[ \mathrm{ClO}^{-}+\mathrm{N}_{2} \mathrm{H}_{4}+2 \mathrm{H}_{2} \mathrm{O} \longrightarrow\mathrm{Cl}^{-}+2 \mathrm{NH}_{3}+4 \mathrm{OH}^{-} \] The product of concern is hydrazine (N₂H₄), which is a toxic compound. This reaction occurs in an alkaline environment, making this a hazardous outcome when bleach and ammonia-containing substances are mixed. In conclusion, household bleach should not be mixed with household ammonia or glass cleansers containing ammonia because the reaction produces toxic hydrazine in an alkaline environment.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Balancing Electron Transfer
To fully grasp the essence of redox reactions in chemistry, it's crucial to understand the principle of balancing electron transfer. The process involves ensuring that the electrons lost by the oxidizing agent are equal to the electrons gained by the reducing agent. In the context of our exercise, we look at two half-reactions involving hydrazine and sodium hypochlorite, each having a transfer of 2 electrons.

This balanced electron transfer signifies that the stoichiometry of the reaction is correct and no further adjustments are needed for the half-reactions to be combined. The alignment of electrons ensures the law of conservation of matter is met, as the total number of electrons remains consistent throughout the reaction.
Combining Half-Reactions
Once the electron transfer is balanced, the next step is combining half-reactions. This involves adding the two half-reactions together while ensuring that the electrons cancel out. In doing so, we're able to see the bigger picture: how reactants transform into products in a full redox reaction.

By combining the half-reactions from our given exercise, we observe that the electrons indeed cancel out, confirming that the previous balancing was done correctly. This step is akin to putting together pieces of a puzzle, ensuring that all components fit to display the complete chemical process.
Reaction Simplification
Reaction simplification serves to streamline the chemical equation, making it easier to interpret and understand. During this phase, we eliminate identical species from both sides of the equation to distill the reaction to its most fundamental components.

In our exercise, the simplification step cancels out water molecules and hydroxide ions that appear on both sides of the combined reaction. What remains is a more concise representation of the transformation, highlighting the key reactants and products without extraneous information. Simplification not only aids clarity but can also be essential in calculating quantities for the reaction.
Hazardous Chemical Reactions
Finally, recognizing hazardous chemical reactions is critical for safety in chemistry. In our textbook example, the mixing of household bleach and ammonia is exceptionally dangerous due to the production of toxic hydrazine.

This reaction underscores the importance of understanding chemical properties and the potential risks when certain substances interact. It's pivotal for students to learn not just the mechanics of chemical reactions, but also their real-world implications and the precautionary measures that should be taken to prevent harm.

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Most popular questions from this chapter

In the electrolysis of an aqueous solution of \(\mathrm{Na}_{2} \mathrm{SO}_{4},\) what reactions occur at the anode and the cathode (assuming standard conditions)? $$\begin{array}{lr} \mathrm{S}_{2} \mathrm{O}_{8}^{2-}+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{SO}_{4}^{2-} & 80^{\circ} \\ \mathrm{O}_{2}+4 \mathrm{H}^{+}+4 \mathrm{e}^{-} \longrightarrow_{2 \mathrm{H}_{2} \mathrm{O}} & 2.01 \mathrm{V} \\ 2 \mathrm{H}_{2} \mathrm{O}+2 \mathrm{e}^{-} \longrightarrow \mathrm{H}_{2}+2 \mathrm{OH}^{-} & -0.83 \mathrm{V} \\ \mathrm{Na}^{+}+\mathrm{e}^{-} \longrightarrow \mathrm{Na} & -2.71 \mathrm{V} \end{array}$$

An electrochemical cell consists of a standard hydrogen electrode and a copper metal electrode. If the copper electrode is placed in a solution of 0.10 \(M\) NaOH that is saturated with \(\mathrm{Cu}(\mathrm{OH})_{2},\) what is the cell potential at \(25^{\circ} \mathrm{C} ?\left[\mathrm{For} \mathrm{Cu}(\mathrm{OH})_{2}\right.\) \(K_{\mathrm{sp}}=1.6 \times 10^{-19} \cdot \mathrm{J}\)

An experimental fuel cell has been designed that uses carbon monoxide as fuel. The overall reaction is $$ 2 \mathrm{CO}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{CO}_{2}(g) $$ The two half-cell reactions are $$ \begin{array}{c} \mathrm{CO}+\mathrm{O}^{2-} \longrightarrow \mathrm{CO}_{2}+2 \mathrm{e}^{-} \\\ \mathrm{O}_{2}+4 \mathrm{e}^{-} \longrightarrow 2 \mathrm{O}^{2-} \end{array} $$ The two half-reactions are carried out in separate compartments connected with a solid mixture of \(\mathrm{CeO}_{2}\) and \(\mathrm{Gd}_{2} \mathrm{O}_{3}\). \(\mathrm{Ox}\) ide ions can move through this solid at high temperatures (about \(800^{\circ} \mathrm{C}\) ). \(\Delta G\) for the overall reaction at \(800^{\circ} \mathrm{C}\) under certain concentration conditions is -380 kJ. Calculate the cell potential for this fuel cell at the same temperature and concentration conditions.

The overall reaction and equilibrium constant value for a hydrogen-oxygen fuel cell at \(298 \mathrm{K}\) is $$ 2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(l) \quad K=1.28 \times 10^{83} $$ a. Calculate \(\mathscr{E}^{\circ}\) and \(\Delta G^{\circ}\) at \(298 \mathrm{K}\) for the fuel cell reaction. b. Predict the signs of \(\Delta H^{\circ}\) and \(\Delta S^{\circ}\) for the fuel cell reaction. c. As temperature increases, does the maximum amount of work obtained from the fuel cell reaction increase, decrease, or remain the same? Explain.

Copper can be plated onto a spoon by placing the spoon in an acidic solution of \(\mathrm{CuSO}_{4}(a q)\) and connecting it to a copper strip via a power source as illustrated below: a. Label the anode and cathode, and describe the direction of the electron flow. b. Write out the chemical equations for the reactions that occur at each electrode.
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