JEE Main 2023 · 1 February · morning · Numerical answer · +4 / −0

Sum of oxidation states of bromine in bromic acid and perbromic acid is ___________.

Answer and solution

Answer 12

Solution

Chemistry ma’am · 4 steps

Name to formula first, then let H at +1 and O at −2 fix the bromine.

  1. Write the formulae. Bromic acid is HBrO₃ and perbromic acid is HBrO₄. The prefix per- means one more oxygen than the "-ic" acid.
  2. Bromic acid. Each molecule is neutral, so all oxidation numbers add to zero. In HBrO₃: (+1) + x + 3(-2) = 0, so x = +5.
  3. Perbromic acid. In HBrO₄: (+1) + x + 4(-2) = 0, so x = +7.
  4. So. The sum is (+5) + (+7) = 12.

The common slip: 10. Taking bromic acid as HBrO₂ (that is bromous acid, Br at +3) gives 3 + 7 = 10, not 12.

The idea to keep. For the oxyacids of a halogen, hypo-ous, -ous, -ic and per-ic acids put the halogen at +1, +3, +5 and +7. Get the formula right and the rest is just adding to zero.

Answer from the NTA final answer key. Solution by PrepWiser.

Study Redox Reactions

Asked about 90 times in JEE Main since 2020. This question is from 2023.