Problem 14 - Chemistry An Atoms First Approach

Question

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).

Step-by-Step Solution

Answer

The balanced equation for the electrolysis of aqueous sodium chloride is: \(2NaCl(aq) + 2H2O(ℓ) → Cl2(g) + H2(g) + 2NaOH(aq)\)

Step 1: Write the half-reactions

First, let's write the half-reactions that occur at the anode and cathode. At the anode, chloride ions are oxidized to produce chlorine gas: 2Cl^(-) → Cl2(g) + 2e^(-) At the cathode, hydrogen ions are reduced to produce hydrogen gas: 2H^(+)+ 2e^(-) → H2(g)

Step 2: Combine half-reactions

Now let's combine the two half-reactions to create the overall balanced equation. To do this, we need to ensure that the number of electrons in each half-reaction is equal. For the anode half-reaction, we have: 2Cl^(-) → Cl2(g) + 2e^(-) For the cathode half-reaction, we have: 2H^(+)+ 2e^(-) → H2(g) No adjustments are needed as the number of electrons is already equal.

Step 3: Write balanced overall equation

Now we will write the overall balanced equation by combining the half-reactions, remembering that the electrons should cancel out: 2Cl^(-) + 2H^(+) → Cl2(g) + H2(g) But we have left out the formation of sodium hydroxide, which also occurs during the electrolysis process. To include this, we need to add sodium ions and hydroxide ions as products to the overall balanced equation: 2Cl^(-) + 2H^(+) + 2Na^(+) → Cl2(g) + H2(g) + 2Na^(+) + 2OH^(-) However, this equation can be simplified by combining the sodium ions with the hydroxide ions, which will form sodium hydroxide: 2NaCl(aq) + 2H2O(ℓ) → Cl2(g) + H2(g) + 2NaOH(aq) This is the balanced equation for the electrolysis of aqueous sodium chloride, demonstrating the formation of chlorine, hydrogen gas, and sodium hydroxide.