redox

Redox reaction

A chemical reaction involving both oxidation and reduction

Oxidation

1. Gains oxygen

2. Loses electrons

3. Loses hydrogen

4. Gains oxidation state

Reduction

Loss of oxygen

Gain electrons

Gain hydrogen

Lose oxidation state

Electrons transfer

• always results in redox reaction

  Remember if the electron has a charge “+’, it needs to lose that amount to form octet .

• If the electron has a charge “-“ , it needs to gain that amount to form octet.

Metals and non metals charge

Metals always positive charge , non metals negative charge

Oxidation state

A number that is assigned to an element in a substance to show its degree of oxidation

Oxidation state of an element

0

Oxygen oxidation state

-2 unless bonded to F then +2

Hydrogen oxidation state

+1 unless bonded to state of H in metals hydride

Oxidising agent

Another substance gets oxidised while it itself gets reduced

Reducing agent

It itself gets oxidised while it reduces another substance

Common oxidising agents

1. Acidified potassium magnate (VII) KMnO4 with H2SO4

2. Acidified potassium dichromate (VI) K2Cr2O7 with H2SO4

3. H2O2 hydrogen peroxide

4. Chlorine

5. Iron 3+

6. Iodine

*reducing agent causes them to change colour

Acidified potassium magnate and sulfuric acid + reducing agent observations

Purple to colour less/ decolorisation

MnO4 -(purple)become Mn 2+(colourless)

Acidified potassium dichromate and sulfuric acid

Orange to green

Cr2O7 2-(orange) to Cr 3+ (green)

Hydrogen peroxide

Remains colourless but causes colour change of a reducing agent

Chlorine

• oxidising agent

• Greenish yellow solution turns colourless

Iodine

Brown to colourless

Oxidising agent

Common reducing agents

1. KI (potassium iodide)

2. H2O2 (hydrogen peroxide)

3. Sulfur dioxide gas / sulphide ion

4. Iron 2+

5. Sodium thiosulfate

*oxidising agent causes them to change colour

Potassium iodide

I- (colouress) into I2 (brown)

Colourless solution turns brown

Hydrogen peroxide

Effervescence of colourless , odour less gas which relights glowing splint. The gas is oxygen

Non redox reactions

1. Neutralisation

2. Acid and carbonate reaction

3. Precipitation reactions

4. Alkali + ammonium salt reactions

5. Decomposition

Ammonium vs ammonia

Ammonium : NH4

Ammonia : NH3