Unit 15 - Electrolysis
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What is an electric current
An electric current is a flow of electrons or ions
What is electrolysis
Electrolysis is the formation of new substances when ionic compounds conduct electricity
Important uses of sodium hydroxide
Manufacture of bleach, paper, and soap
Important uses of chlorine
Sterilising public water supplies manufacture of bleach and hydrochloric acid
What is one faraday (1F)
1 faraday = 1 mole of electrons
Describe a simple electrolysis of a molten salt
• One the salt is molten there are free ions and a current can flow • electrodes are made of unreactive carbon • positive ions (cations) go to the negative electrode (cathode) • negative ions (anions) go to the positive electrode (anode)
Describe simple electrolysis using aqueous solutions
In aqueous solutions, as well as ions from the compound there are H+ and OH- ions At the cathode the metal will be formed only if it is LESS REACTIVE than hydrogen (otherwise H2 gas is formed) At the anode there will be water and oxygen formed from the OH- ions UNLESS there are hailide ions (Cl-, Br-, I-) present in which case molecules of them will be formed
The manufacture of of sodium hydroxide and chlorine by electrolysis
A sodium chloride solution called brine is put into the diaphragm cell and electrolysis is done on it Chlorine is made at the anode and hydrogen is made at the cathode, some NaCl is left in the solution at the end