Ch.20 - Electrochemistry

Problem 98

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Chapter 20, Problem 98

What products are obtained in the electrolysis of a molten mixture of KI and KBr?

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Step 1: Understand the process of electrolysis. Electrolysis is a process that uses an electric current to drive a non-spontaneous chemical reaction. In this case, the electrolysis of a molten mixture of KI (potassium iodide) and KBr (potassium bromide) will produce elemental potassium, iodine, and bromine.

Step 2: Identify the ions present in the molten mixture. The molten mixture of KI and KBr will contain K+ ions, I- ions, and Br- ions.

Step 3: Determine the reactions at the electrodes. At the cathode (negative electrode), the K+ ions will gain electrons to form elemental potassium (K). This is a reduction reaction. At the anode (positive electrode), the I- and Br- ions will lose electrons to form elemental iodine (I2) and bromine (Br2). These are oxidation reactions.

Step 4: Write the half-reactions. The half-reaction at the cathode is K+ + e- -> K. The half-reactions at the anode are 2I- -> I2 + 2e- and 2Br- -> Br2 + 2e-.

Step 5: Combine the half-reactions to get the overall reaction. The overall reaction is 2K+ + 2I- + 2Br- -> 2K + I2 + Br2.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electrolysis

Electrolysis is a chemical process that uses electrical energy to drive a non-spontaneous reaction. In this process, an electric current is passed through an electrolyte, causing the decomposition of the compound into its constituent elements or ions. The products formed depend on the nature of the electrolyte and the electrodes used.

Ionic Compounds

Ionic compounds, such as potassium iodide (KI) and potassium bromide (KBr), consist of positively and negatively charged ions held together by ionic bonds. When molten, these compounds dissociate into their respective ions, allowing them to conduct electricity. The behavior of these ions during electrolysis is crucial for predicting the products formed.

Electrode Reactions

During electrolysis, reactions occur at the electrodes: oxidation at the anode and reduction at the cathode. For a molten mixture of KI and KBr, potassium ions (K+) migrate to the cathode to gain electrons, while bromide (Br-) and iodide (I-) ions migrate to the anode to lose electrons. The specific products formed depend on the relative reactivity of the ions involved.

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