A dilute solution of sulfuric acid contains hydrogen ions,
hydroxide ions and sulfate ions.
When this solution is electrolysed, hydrogen gas is formed
at the cathode and oxygen gas is formed at the anode.
(a) Explain why hydrogen is formed at the cathode.
(b) Write the ionic equation for the reaction at the anode.
Answers
Answer:
The electrolysis of acidified water
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2. Using an electrolysis cell - investigating the electrolysis of acidified water (dilute sulfuric acid)
AND the aqueous solutions of certain sulfate salts of reactive metals e.g. sodium sulfate, magnesium sulfate and strong alkalis like sodium hydroxide.
The electrolysis of dilute sulfuric acid is described and explained. This is the classic 'electrolysis of water' experiment and good introduction to electrolysis experiment. The electrode products and electrode equations for the electrolysis of water are quoted. What are the products of the electrolysis of water acidified with dil. sulfuric acid? All the electrode equations for the electrolysis of water are explained and diagrams of the apparatus.
Reminders: Electrolysis (of acidified water) is a way of splitting up (decomposition) of the compound (water) using electrical energy. The electrical energy comes from a d.c. (direct current) battery or power pack supply. A conducting liquid, containing ions, called the electrolyte (dilute sulfuric acid), must contain the compound (water) that is being broken down. The electricity must flow through electrodes dipped into the electrolyte to complete the electrical circuit with the battery. Electrolysis can only happen when the circuit is complete, and an electrical current (electricity) is flowing, then the products of electrolysing dil. sulfuric acid are released on the electrode surfaces where they can be collected. Electrolysis always involves a flow of electrons in the external wires and electrodes and a flow of ions in the electrolyte and there is always a reduction at the negative cathode electrode (which attracts positive ions, cations) and an oxidation at the positive anode electrode (which attracts negative ions, anions) and it is the ions which are discharged to give the products
Explanation:
Electrolysis of dilute sulfuric acid - the products of electrolysing water acidified with sulfuric acid are hydrogen gas and oxygen gas
Two experimental setups are described, the Hofmann voltammeter demonstration (left diagram) and a simple cell (right diagram) for use in schools and colleges for pupils to use. Dilute sulfuric acid is used as the electrolyte in this investigation. The Hofmann voltammeter is filled with the electrolyte (sulfuric acid) by opening the taps at the top of the outer tubes to allow any gas to escape. The gases formed on the electrolysis of the dilute sulfuric acid can be collected via the same taps. The platinum or carbon electrodes are inert.
You need inert (non–reactive) electrodes like platinum (left) and much cheaper carbon (graphite electrodes, right). In the simple electrolysis cell, the graphite (carbon) electrodes are, through a large rubber bung, 'upwardly' dipped into an solution of acidified water. In this cheap and simple apparatus the gaseous products (hydrogen and oxygen) are collected in small test tubes inverted over the carbon electrodes. You have to fill the little test tubes with the electrolyte (dil. sulfuric acid), hold the liquid in with your finger and carefully invert them over the nearly full electrolysis cell. The gases can be collected and tested.