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Redox Reactions

AIPMT 2015MCQMedium📈 Topic in 12% papers+4−1
Ques. 1AIPMT 2015

Assuming complete ionisation, same moles of which of the following compounds will require the least amount of acidified KMnO4 for complete oxidation?

  1. FeSO3
  2. FeC2O4
  3. Fe(NO2)2
  4. FeSO4

Answer

(4) FeSO4

Solution

Acidified KMnO4 oxidises every reducing species present; the amount needed is proportional to the total loss of electrons (n-factor) per mole.

FeSO3: Fe2+ Fe3+ (1 e-) and SO32- SO42- (2 e-) ⇒ n = 3

FeC2O4: Fe2+ Fe3+ (1 e-) and C2O42- 2CO2 (2 e-) ⇒ n = 3

Fe(NO2)2: Fe2+ Fe3+ (1 e-) and 2NO2- 2NO3- (2 2 = 4 e-) ⇒ n = 5

FeSO4: only Fe2+ Fe3+ (1 e-); SO42- cannot be oxidised further ⇒ n = 1

∴ FeSO4 has the smallest n-factor and needs the least KMnO4.

Answer: (4)

Keep practising — Redox Reactions

Ques. 2AIPMT 2015 (Cancelled)

Which of the following processes does not involve oxidation of iron?

  1. Formation of Fe(CO)5 from Fe.
  2. Liberation of H2 from steam by iron at high temperature.
  3. Rusting of iron sheets.
  4. Decolourisation of blue CuSO4 solution by iron.
Ques. 3AIPMT 2014

The pair of compounds that can exist together is

  1. FeCl3, SnCl2
  2. HgCl2, SnCl2
  3. FeCl2, SnCl2
  4. FeCl3, KI
Ques. 4AIPMT 2014

In acidic medium, H2O2 changes Cr2O72- to CrO5 which has two (-O-O-) bonds. Oxidation state of Cr in CrO5 is

  1. +5
  2. +3
  3. +6
  4. -10
Ques. 5AIPMT 2012 (Prelims)

When Cl2 gas reacts with hot and concentrated sodium hydroxide solution, the oxidation number of chlorine changes from

  1. zero to +1 and zero to −5
  2. zero to −1 and zero to +5
  3. zero to −1 and zero to +3
  4. zero to +1 and zero to −3
Ques. 6AIPMT 2012 (Prelims)

A mixture of potassium chlorate, oxalic acid and sulphuric acid is heated. During the reaction which element undergoes maximum change in the oxidation number?

  1. S
  2. H
  3. Cl
  4. C
Ques. 7AIPMT 2012 (Prelims)

In which of the following compounds, nitrogen exhibits highest oxidation state?

  1. N2H4
  2. NH3
  3. N3H
  4. NH2OH
Ques. 8AIPMT 2009

Oxidation numbers of P in PO43-, of S in SO42- and that of Cr in Cr2O72- are respectively

  1. +3, +6 and +5
  2. +5, +3 and +6
  3. –3, +6 and +6
  4. +5, +6 and +6
Ques. 9AIPMT 2008

Number of moles of MnO4- required to oxidize one mole of ferrous oxalate completely in acidic medium will be

  1. 7.5 moles
  2. 0.2 moles
  3. 0.6 moles
  4. 0.4 moles
Ques. 10AIPMT 2004

Which is the best description of the behaviour of bromine in the reaction given below? H2O + Br2 HOBr + HBr

  1. Proton acceptor only
  2. Both oxidised and reduced
  3. Oxidised only
  4. Reduced only
Ques. 11AIPMT 2003

The oxidation states of sulphur in the anions SO32-, S2O42- and S2O62- follow the order

  1. S2O42- < SO32- < S2O62-
  2. SO32- < S2O42- < S2O62-
  3. S2O42- < S2O62- < SO32-
  4. S2O62- < S2O42- < SO32-

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