Question 1

Q1. Assign oxidation number to each of the following species:
(a) NaH₂PO₄
(b) NaHSO₄
(c) H₄P₂O₇
(d) K₂MnO₄
(e) CaC₂O₄
(f) NaBH₄

Accepted Answer

The oxidation numbers for the specified elements in each species are as follows:
(a) In NaH₂PO₄, the oxidation number of P is +5.
(b) In NaHSO₄, the oxidation number of S is +6.
(c) In H₄P₂O₇, the oxidation number of P is +5.
(d) In K₂MnO₄, the oxidation number of Mn is +6.
(e) In CaC₂O₄, the oxidation number of C is +3.
(f) In NaBH₄, the oxidation number of B is +3.

Question 2

Q2. What are the oxidation number of the elements in the following compounds/ions?
(a) ClO₃⁻
(b) N₂H₄
(c) NO₃⁻

Accepted Answer

The oxidation numbers for the specified elements in each species are as follows:
(a) In ClO₃⁻, the oxidation number of Cl is +5.
(b) In N₂H₄, the oxidation number of N is -2.
(c) In NO₃⁻, the oxidation number of N is +5.

Question 3

Q3. Justify that the following reactions are redox reactions:
(a) CuO(s) + H₂(g) → Cu(s) + H₂O(g)
(b) Fe₂O₃(s) + 3CO(g) → 2Fe(s) + 3CO₂(g)
(c) 4BCl₃(g) + 3LiAlH₄(s) → 2B₂H₆(g) + 3Li

Accepted Answer

A redox reaction is a chemical reaction in which the oxidation states of atoms are changed. This involves both reduction (decrease in oxidation number) and oxidation (increase in oxidation number) occurring simultaneously. We can justify each reaction as a redox reaction by assigning oxidation numbers to the elements involved and observing the changes.

Question 4

Q4. Fluorine reacts with ice and results in the change: H₂O(s) + F₂(g) → HF(g) + HOF(g). Justify that this reaction is a redox reaction.

Accepted Answer

To justify that the reaction H₂O(s) + F₂(g) → HF(g) + HOF(g) is a redox reaction, we need to determine the oxidation numbers of the elements involved in the reactants and products and observe any changes. A redox reaction involves both oxidation (increase in oxidation number) and reduction (decrease in oxidation number) occurring simultaneously.

Question 5

Q5. Calculate the oxidation number of sulphur, chromium and nitrogen in H₂SO₅, Cr₂O₇²⁻ and NO₃⁻. Suggest structure of H₂SO₅. Comment on the oxidation state of sulphur in H₂SO₅.

Accepted Answer

We will calculate the oxidation numbers for the specified elements in each species. For H₂SO₅, we will also suggest its structure and comment on the actual oxidation state of sulfur.

Question 6

Q6. Justify that the following reactions are redox reactions:
(a) CuO(s) + H₂(g) → Cu(s) + H₂O(g)
(b) Fe₂O₃(s) + 3CO(g) → 2Fe(s) + 3CO₂(g)
(c) 4BCl₃(g) + 3LiAlH₄(s) → 2B₂H₆(g) + 3Li

Accepted Answer

A redox reaction is a reaction in which both oxidation and reduction occur simultaneously. Oxidation involves an increase in oxidation number (loss of electrons), while reduction involves a decrease in oxidation number (gain of electrons). We can justify these reactions as redox reactions by calculating the oxidation numbers of the elements involved and observing changes.

**(a) CuO(s) + H₂(g) → Cu(s) + H₂O(g)**
*   **Reactants:**
    *   In CuO: Oxygen is -2, so Copper (Cu) is +2.
    *   In H₂: Hydrogen (H) is 0 (elemental state).
*   **Products:**
    *   In Cu: Copper (Cu) is 0 (elemental state).
    *   In H₂O: Oxygen is -2, so Hydrogen (H) is +1.

*   **Changes in Oxidation Numbers:**
    *   Cu: +2 (in CuO) → 0 (in Cu)  (Decrease in oxidation number, hence **reduction**)
    *   H: 0 (in H₂) → +1 (in H₂O) (Increase in oxidation number, hence **oxidation**)