Chemguide: Support for CIE A level Chemistry

Learning outcome 24: Electrochemistry

24.1: Electrolysis

Learning outcome 24.1.1

This statement is about what substances are produced during electrolysis.

Before you go on, you should find and read the statement in your copy of the syllabus.

You will find this on two Chemguide pages: Electrolysis of molten compounds and Electrolysis of solutions.

You will probably find a lot of this is familiar from courses you have done in the past.

Which equation you should use in reactions producing hydrogen or oxygen from the water?

I suggest that with CIE you should use the equations showing the hydrogen or oxygen coming directly from the water especially if they talk about, say, a "neutral solution of sodium chloride".

There was one question involving sodium chloride solution where they only gave the mark for this equation:

. . . and not for this one:

Similarly, you would probably be safer to use this equation for the discharge of hydrogen in the electrolysis of, say, magnesium sulfate solution:

. . . rather than this one:

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© Jim Clark 2020