A space shuttle’s upward thrust came from the following reaction between aluminium and ammonium perchlorate.

$$\ce{10 Al + 6 NH4ClO4 → 4 Al2O3 + 2 AlCl3 + 12 H2O + 3 N2}$$

Which statements about this reaction are correct?

  1. Aluminium is oxidised.
  2. Chlorine is reduced.
  3. Nitrogen is oxidised.

I understand why aluminium is oxidized, but why are 2 and 3 wrong?

  • 4
    $\begingroup$ They aren't. Isn't there an "all of the above" answer? $\endgroup$
    – Ian Bush
    Aug 14, 2020 at 8:13
  • $\begingroup$ No there isn't. $\endgroup$
    – Jana
    Aug 14, 2020 at 8:17
  • 2
    $\begingroup$ Well the question as written does not require just one of them to be correct $\endgroup$
    – Ian Bush
    Aug 14, 2020 at 8:25
  • 1
    $\begingroup$ Notice there is "which statements ...are", not "which statement .. is". The question implies more than one possibility. $\endgroup$
    – Poutnik
    Aug 14, 2020 at 8:29
  • 1
    $\begingroup$ @andselisk this is straight from Cambridge so I don't think so $\endgroup$
    – Jana
    Aug 14, 2020 at 8:32

1 Answer 1



  1. The oxidation number of chlorine in the perchlorate radical is +7 whereas, in the product side, chlorine has an oxidation number of minus 1 in AlCl3. As the oxidation number is reduced by 8 here (gaining 8 electrons), chlorine is, indeed, reduced.

  2. Nitrogen has an oxidation state of minus 3 in NH4ClO4 whereas, it has an oxidation state of 0 in N2 molecule in the product side. Here, the oxidation number of nitrogen has increased by 3 via losing 3 electrons. So, Nitrogen here is oxidised.

Hence, all the options are correct.


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