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Chapter 20: Problem 14

The electrolysis of aqueous sodium chloride (brine) is an important industrial process for the production of chlorine and sodium hydroxide. In fact, this process is the second largest consumer of electricity in the United States, after the production of aluminum. Write a balanced equation for the electrolysis of aqueous sodium chloride (hydrogen gas is also produced).

Short Answer

Expert verified
The balanced equation for the electrolysis of aqueous sodium chloride is: \(2Cl^-(aq) + 2H_2O(l) \rightarrow Cl_2(g) + H_2(g) + 2OH^-(aq)\).

Step by step solution

01

Identify the half-reactions

For the electrolysis of aqueous sodium chloride, two half-reactions occur - one at the anode where oxidation takes place and one at the cathode where reduction takes place. At the anode (the positively-charged electrode), chloride ions (Cl⁻) are oxidized to form chlorine gas (Cl₂). The half-reaction is: Cl⁻(aq) → 1/2 Cl₂(g) + e⁻ At the cathode (the negatively-charged electrode), water molecules (H₂O) are reduced to form hydrogen gas (H₂) and hydroxide ions (OH⁻): 2H₂O(l) + 2e⁻ → H₂(g) + 2OH⁻(aq)
02

Balance the half-reactions

The half-reactions above are already balanced in terms of mass and charge. Notice that each half-reaction has the appropriate number of electrons (e⁻) on each side of the reaction.
03

Combine the half-reactions

Now we need to combine the half-reactions to form the overall balanced equation for the electrolysis of aqueous sodium chloride. To do this, we must first make sure that the number of electrons in both half-reactions is equal. Currently, the anode half-reaction has 1 electron while the cathode half-reaction has 2 electrons. In order to balance the number of electrons, we will multiply the anode half-reaction by 2: 2Cl⁻(aq) → Cl₂(g) + 2e⁻ Now, we can add the two half-reactions together: 2Cl⁻(aq) + 2H₂O(l) + 2e⁻ → Cl₂(g) + 2e⁻ + H₂(g) + 2OH⁻(aq)
04

Simplify the equation

Lastly, simplify the equation by removing the electrons, as they are present on both sides of the equation: 2Cl⁻(aq) + 2H₂O(l) → Cl₂(g) + H₂(g) + 2OH⁻(aq) This is the balanced equation for the electrolysis of aqueous sodium chloride.

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Most popular questions from this chapter

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What is a disproportionation reaction? Use the following reduction potentials \(\mathrm{ClO}_{3}^{-}+3 \mathrm{H}^{+}+2 \mathrm{e}^{-} \longrightarrow \mathrm{HClO}_{2}+\mathrm{H}_{2} \mathrm{O} \quad \mathscr{E}^{\circ}=1.21 \mathrm{~V}\) \(\mathrm{HClO}_{2}+2 \mathrm{H}^{+}+2 \mathrm{e}^{-} \longrightarrow \mathrm{HClO}+\mathrm{H}_{2} \mathrm{O} \quad \mathscr{E}^{\circ}=1.65 \mathrm{~V}\) to predict whether \(\mathrm{HClO}_{2}\) will disproportionate.
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