Chapter 15 - Oxidation-Reduction

Question 1

Potassium permanganate

Answer 1

Oxidising agent
Purple colored
Not a primary standard
Unstable
Self-indicating
Decomposes in the presence of sunlight 
Concentrations vary over time 
Self-indicating 
Good oxidizing agent so we use fairly dilute solutions

Question 2

Primary standard

Answer 2

Can be obtained in a state of very high purity

Question 3

Equation for potassium permanganate

Answer 3

MnO4 + 8H+ + 5e- —>Mn2+ + 4H2O

Question 4

What supplies the H+ ions

Answer 4

Dilute acid e.g. sulfuric acid

Question 5

The MnO4 changes from

Answer 5

+7 to +4 to +2

Question 6

Ratio of MnO4- ions + Fe2+ ions

Answer 6

1:5

Question 7

Iron sulfate

Answer 7

Crystals are oxidized slowly by the air

Efflorescence - lose water of crystallization spontaneously to air

Question 8

Deliquescence

Answer 8

Takes in moisture from the air

e.g. FeSO4

Question 9

Ammonium iron sulfate

Answer 9

Primary standard
High relative molecular mass reduces inaccuracies in weighing
Does not effluoresce

Question 10

What do iron tablets have

Answer 10

A coating to slow down the rate at which they dissolve in the stomach

Question 11

Sodium Thiosulfate

Answer 11

Reducing Agent 
Analyse the amount of substances dissolved in water
Colourless crystalline solid
Not a primary standard
Indicator is starch

Question 12

Iodine

Answer 12

Slightly vaporises
Goes from solid to gas
insoluble in water

Question 13

Why Potassium Iodide should be in excess

Answer 13

All the KMnO4 reacts completely with the I- ions to maximise the I2
Iodine is soluble in potassium iodide
To keep in solution the iodine produced

Question 14

Colour Change of Sodium Thiosulfate

Answer 14

Red/brown to yellow to colourless