Redox Reactions

This is a Short answer type question as classified in NCERT Exemplar

(i) 2Mn0^–₄ + 5S0₂ + 2H₂0 + H⁺?5HS0^–₄ + 2Mn²⁺
Balancing by ion-electron method:

(ii) We can balance the given reaction by oxidation number method-

Balancing by oxidation number method as to make the electron gain and loss equal as given

3N₂H₄ + 4ClO₃^- → 6NO + 4Cl^- + 6H₂O

The balanced chemical is given as-

(iii) We can balance the given reaction by ion electron method as

Cl₂O₇(g) + H₂O₂ (aq) → ClO₂^- +O₂ (acidic medium)

Balancing bu ion electron method

2 * { Cl₂O₇ + 6H⁺ + 8e^- → 2ClO₂^- + 3H₂O

8  * { H₂O₂ → O₂ + 2H⁺ + 2e^- 

The balanced chemical is given as-

2Cl₂O₇ + 12H⁺ + 16e^- → 4ClO₂^- + 6H₂O

                         8H₂O₂ → 8O₂ + 16H⁺ + 16e^-

          2Cl₂O₇ + 8H₂O₂ → 4ClO₂^- + 6H₂O + 8O₂ + 4H⁺

This is a Long answer type question as classified in NCERT Exemplar

We can Measure the electrode potential of the given species by connecting the redox couple of the given species with standard hydrogen electrode. If it is positive, the electrode of the given species acts as reductant and if it is negative, it acts as an oxidant.  Find the electrode potentials of the other given species in the same way, compare the values and determine their comparative strength as an reductant or oxidant. Example Measurement of standard electrode potential of electrode E? _Zn2+/Zn using SHE as a reference electrode.

Types of Redox Reactions

The different types of Redox Reactions are:

Decomposition Reaction

Combination Reaction

Displacement Reaction

Disproportionation Reactions

This is a Long answer type question as classified in NCERT Exemplar

We can calculate the oxidation states by - ]

NaClO₄ Oxidation no. of chlorine = +7 

Suppose oxidation number of chlorine is x then,  1 + x + 4 * (−2) = 0

∴ x - 7 = 0 

    x = +7

We can calculate, the oxidation states, as given below-

NaClO₃ Oxidation no. of chlorine = +5

? NaClO Oxidation no. of chlorine = +1

? KClO₂ Oxidation no. of chlorine = +3

? Cl₂O₇ Oxidation no. of chlorine = +7

ClO₃ Oxidation no. of chlorine = +6

Cl₂O Oxidation no. of chlorine = +1 

NaCl Oxidation no. of chlorine = −1

Cl₂ Oxidation no. of chlorine = 0

ClO₂ Oxidation no. of chlorine = +4.

Oxidation state (+2) is not present in any of the above compounds.

This is a Long answer type question as classified in NCERT Exemplar

Disproportionate is defined as the reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states So, to occur such type of redox reaction, the element should exist in at least three oxidation states. So that element present in the intermediate state and it can change to both higher and lower oxidation state during disproportionate reaction. Fluorine is the most electronegative element and a strong oxidizing agent and is the smallest in size of all the halogens. It does not show a positive oxidation state (shows only −1 oxidation state) and hence, does not undergo disproportionate reaction.