Electrolysis (continued)
Overview
Electrolysing a molten salt is one thing, but most real electrolysis is done in water solutions, where there is an extra player: the water itself. This makes the products less obvious, because hydrogen and oxygen can appear alongside, or instead of, the ions you started with.
In this lesson you will build on the basics to predict the products of electrolysing aqueous solutions, learn the rules that decide what forms at each electrode, and see how electrolysis is used in electroplating to coat objects with metal.
Objectives
- Identify the products formed at the electrodes and describe the observations made during the electrolysis of: (a) molten lead(II) bromide (b) concentrated aqueous sodium chloride (c) dilute sulfuric acid using inert electrodes made of platinum or carbon / graphite.
- State that metals or hydrogen are formed at the cathode and that non-metals (other than hydrogen) are formed at the anode.
- Predict the identity of the products at each electrode for the electrolysis of a binary compound in the molten state.
- State that metal objects are electroplated to improve their appearance and resistance to corrosion.
- Describe how metals are electroplated.
- [Supplement] Identify the products formed at the electrodes and describe the observations made during the electrolysis of aqueous copper(II) sulfate using inert carbon / graphite electrodes and when using copper electrodes.
- [Supplement] Predict the identity of the products at each electrode for the electrolysis of a halide compound in dilute or concentrated aqueous solution.
- [Supplement] Construct ionic half-equations for reactions at the anode (to show oxidation) and at the cathode (to show reduction).
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Lesson Evaluation
Congratulations on completing the lesson on Electrolysis (continued). Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- Why can electrolysing a solution give different products from the molten compound? A. The current is higher B. Water provides extra hydrogen and hydroxide ions C. The temperature is lower D. The electrodes react Answer: B
- At the cathode, if the metal is very reactive (such as sodium), the product is: A. The metal B. Hydrogen C. Oxygen D. Chlorine Answer: B
- When concentrated sodium chloride solution is electrolysed, the anode product is: A. Oxygen B. Hydrogen C. Chlorine D. Sodium Answer: C
- When copper(II) sulfate solution is electrolysed with inert electrodes, the cathode product is: A. Hydrogen B. Copper C. Oxygen D. Sulfur Answer: B
- In electroplating, the object to be coated is made the: A. Anode B. Cathode C. Electrolyte D. Power supply Answer: B
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