Question

# (a) Al3+, Cu2+, Na+, Zn2+ ions are present in an aqueous solution, such that the concentration of ions is same. write the order of discharge of ions. (b) Amongst the OH− ions and Br− ions which are likely to discharge first?

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Solution

## (a) The order of discharge of metallic ions (cations) depends on their position in the electrochemical series. If the concentration of the ions is equal, the cation located lower in the electrochemical series gets discharged first (as it easily gains electrons) at the respective electrodes, followed by the other cations in the series, in decreasing order. Since the order of reactivity of cations is Na+ >Al3+>Zn2+>Cu2+, thus, Cu2+ion being at the lowest position of the electrochemical series would get discharged first and Na+ ion, being at the top, gets discharged last. (b) The order of discharge of anions depends on the position of the anions in the electrochemical series. The anion located lower in the electrochemical series gets discharged first (as these easily lose electrons) at the respective electrodes, followed by the other anions in the series, in decreasing order. ${\mathrm{OH}}^{-}$ ion is placed below bromide ion in the series, hence it easily loses electrons and is likely to discharge earlier than bromide ion.

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