Redox Reactions Test - 4

This is redox couple.

Where following reaction take place :

Zn²⁺  + 2e^{-  →} Zn

Current is taken at the direction in which positive charge is flowing, but electrons are negatively charged. So, the direction of current and the direction of electron flow is opposite. 

The flow of current is possible only due to potential difference.

Oxidation state of O in OF₂ is +2 and O₂F₂ is +1. Because the number assigned to oxygen will depend upon the bonding state of oxygen.

In the superoxide ion, O₂⁻, the oxygen has an oxidation number of −¹/₂. The stability of metal superoxides depends on the size and the electropositive character of the metal. The larger the metal and the more electropositive it is, the greater the stability of its superoxide. 

Oxidation state of P in NaH₂PO₄ is +5.

Solution : 

Let the oxidation number of P be x. As we already know oxidation number of other atoms so we can calculate that of P too.

Na = +1

H= +1 (+2 for hydrogen molecule)

O = -2

Now calculating oxidation number of P:-

1 +2 + x +(-8) = 0

On solving we get x= +5.

Oxidation state of S in KAl(SO₄)₂.12H₂O is +6.

As, Oxidation number of S in KAl(SO₄)₂.12 H2O can be calculated as-

1 + 3 + 2X-16   +  0 = 0  (H₂O is neutral so oxidation No. is 0)

2X=12

X  = +6

Whenever a reaction between an oxidising agent and a reducing agent is carried out, a compound of lower oxidation state is formed if the reducing agent is in excess and a compound of higher oxidation state is formed if the oxidising agent is in excess. This can be illustrated as follows:

 P₄ and F₂ are reducing and oxidising agents respectively. If an excess of P₄ is treated with F₂, then PF₃ will be produced, wherein the oxidation number (O.N.) of P is +3.
PF₄(excess)+F₂→PF₃

The reaction is not redox because there is no oxidation or reduction of any element (i.e. no change in oxidation state/number). 

Ba in BaCl₂ is at a +2 charge because it is in group 2. On the other side of the equation Ba in BaSO₄ is still +2. Cl₂ on the first side of the equation is -2 (as 2 chlorines) and Cl is -2 on the other side as there are 2 of them. 

H on both sides are both +1 (but technically +2 as there are two of them). 

SO₄ does not change oxidation number and always remains -2. 

So, the reaction is not a redox reaction.

The electrochemical process for extraction of metal or non-metal from its ore involves the redox reaction i.e. oxidation and reduction takes place simultaneously. For example, extraction of Na and Cl₂ from NaCl.