IGCSE Chemistry 0620/21/O/N/21 Q10

Question

10 Which statements about the products of electrolysis, using inert electrodes, are correct?

1. When molten lead(II) bromide is electrolysed, bromine is formed at the cathode.
2. When dilute sulfuric acid is electrolysed, oxygen is formed at the anode.
3. When concentrated aqueous sodium chloride is electrolysed, sodium is formed at
the cathode.
4. When concentrated hydrochloric acid is electrolysed, chlorine is formed at the
anode.

A 1 and 2     B 1 and 3     C 2 and 4     D 3 and 4

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Answer ( 1 )

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    2022-05-11T12:35:22+08:00
    This answer is edited.

    In electrolysis…

    – of molten lead (II) bromide, Pb2+ will go to the cathode, Br- will go to the anode. Hence, Br- ions discharge at the anode to become bromine gas, not at the cathode. (1 is false)

    – of dilute sulphuric acid,  H+ ions go to the cathode, OH- and SO4 2- ions move to the anode. OH- is chosen to discharge at the anode, hence oxygen gas is formed at the anode. (2 is true)

    – of concentrated aqueous sodium chloride, Na+ and H+ ions move to the cathode, OH- an Cl- ions move to the anode. H+ ions are chosen to gain electrons at the cathode to form hydrogen gas, not Na+ ions. Cl- ions are chosen to discharge at the anode to form chlorine gas.  Concentration of aqueous electrolyte doesn’t affect cations. (3 is false)

    – of concentrated hydrochloric acid, H+ ions move to the cathode, Cl- and OH- ions move to the anode. Cl- is chosen to discharge at the anode, forming chlorine gas. (4 is true)

    Ans: C 2 and 4

     

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