Redox reaction (oxygen and hydrogen atom)

Learning Objectives:

(a)

define

oxidation

and

reduction

(redox)

in

terms

of

oxygen/hydrogen gain/loss.

(b) define redox in terms of electron transfer and changes in

oxidation number / state.

(c) describe the use of aqueous potassium iodide and acidified

potassium

dichromate(VI)

in

testing

for

oxidising

and

reducing agents from the resulting colour changes.

Redox reaction (pg 1)

Oxidation

Reduction

Gains of oxygen

Loss of oxygen

Loss of hydrogen

Gain of hydrogen

Loss of electrons

Gain of electrons

Increase in oxidation
state/number

Decrease in oxidation
state/number

Happens when a substance GETS
oxidised

Happens when a substance GETS
reduced

Redox Reactions

• In a redox reaction, one species is always oxidised and another species is
always reduced.

• Hence, we describe them as redox reaction.

Mg(s) + H2O(g) → MgO(s) + H2(g)

A redox reaction has taken place.

Water has lost oxygen
and is reduced to
hydrogen.

Magnesium has gained
oxygen and is oxidised
to magnesium oxide.

Mg (s) + CuO (s) → MgO (s) + Cu ( s)

Concept 1 Q1 : Gain of Oxygen / Loss of Oxygen (notes)

Mg has been oxidised to MgO as there is a gain of oxygen.
This process is called oxidation.

CuO has been reduced to Cu as there is a lost of oxygen.
This process is called reduction.

Watch this video:

​https://youtu.be/Lak04nkLxhY?t=152

2NH3(g) + 3CuO(s) → N2(g) + 3Cu(s) + 2H2O(g)

NH3 has lost hydrogen to form N2.
It has been oxidised.

Concept 2 : Loss of Hydrogen/ Loss of Oxygen

CuO has lost oxygen to form Cu
It has been reduced.

By

Product

Watch this video:

https://www.youtube.com/watch?v=fvvbeLh0D4w

Watch this video:

​https://youtu.be/Lak04nkLxhY?t=152

Watch this video:

​https://youtu.be/Lak04nkLxhY?t=152

Activating Prior Knowledge
(10 min)

Mg

Mg has gained oxygen to form MgO

PbO

PbO has lost oxygen to form Pb

Activating Prior Knowledge
(10 min)

H2S

H2S has lost hydrogen to form S

Cl2

Cl2 has gain hydrogen to form HCl