Electrochemistry: Oxidation, Reduction, Oxidation state, Rule for Assigning Oxidation State

Question: Define oxidation and reduction.

Answer

Oxidation may be defined as

i. Loss of electron

ii. Loss of hydrogen

iii. Gain of oxygen

Reduction may be defined as

i. Gain of electron

ii. Gain of hydrogen

iii, Loss of oxygen

Question: Define oxidation and reduction in terms of loss or gain of electron

Answer

Oxidation

A process hat involves the loss of electrons from an element is called oxidation. For example group IA and IIA group elements loss one and two electron to form cation.

Reduction

The process that involves the gain of electron by a substance is called reduction.

Elements of group VIA and VIIA elements gain one and two electrons, respectively to form a anion during the reduction reaction.

Question: Define oxidation state and what are rules for assigning Oxidation State.?

Oxidation state

Oxidation state or oxidation number may be define as

The number of charge that an element has in a molecule or compound.

Rules for assigning Oxidation State

1. Oxidation states of any uncombined free element is always zero. Oxidation state of Zn,Na, H2 etc is zero.

2. Oxidation state of simple or complex ion is the same as charge on their ions. e.g., oxidation state of Na+ is +1, oxidation state of CO2- is -2.

3. Oxidation state of complex ion is equal to sum of oxidation states of all atoms present in it. For example, in CO3 2-, O. S. of C = +4, O. S of O = -2

So,

O.S. of C + 3(O.S. of O) = O. S. of complex ion

+4 + 3(-2) = -2

+4 -6 = -2

-2 = -2

4. Oxidation state of a neutral molecule is zero and it is equal to sum of oxidation states of all atoms present in it.

In HCl, O.S. of H = +1 and O.S. of Cl =-1, so oxidation state of HCl is zero i.e.,

O.S. of H + O.S. of Cl = +1 + (-1) = 0

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