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Need help with a chemistry question-electrolysis GCSE watch

    • Thread Starter

    I'm currently just revising topics of chemistry in the summer because its the only time I can get things done but I'm stuck on a question for Electrolysis.

    In what situation will hydrogen gas be given out during the electrolysis of an aqueous solution of an ionic solid?

    It depends on the relative reactivities of H+ (from the water) and any other cations present.

    Electrolysis of solutions:
    • Many ionic substances have very high melting points which takes a lot of energy to melt them and free the ions to move to electrodes in electrolysis. However, some ionic substances dissolve in water and when this happens, the ions also become free to move around.
    • In electrolysis only metal of very low reactivity, below hydrogen in the reactivity series are deposited from their aqueous solutions.
    • For example, when we electrolyse an aqueous solution of copper (ll) bromide, copper ions, Cu2+, move to the cathode and the bromide ions, Br–, move to the anode. Copper (ll) bromide is split into its elements at the electrodes shown in the figure below:

    Copper (ll) bromide → copper + bromide
    CuBr2 (l) → Cu (s) + Br2 (aq)
    The state symbols in the given equation shows that the copper bromide is dissolved in water and the copper formed is solid and the bromine formed dissolves in the water.
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