Redox titrations

Question 0

Colour change between manganate and iron in dilute

Answer 0

Mn is purple and Fe is colourless, Mn turns colourless as does Fe

Question 1

Equations for manganate (vii) and iron (II)

Answer 1

Reduction: MnO4- + 8H+ + 5e- –> Mn2+ + 4H2O
Oxidation: Fe2+ –> Fe3+ + e-

Question 2

Colour change between manganate and iron at higher conc.

Answer 2

Fe2+ is pale green, fe3+ is yellow and Mn2+ is pale pink

Question 3

Oxidation of ethanedioic acid equation

Answer 3

C2O42- –> 2CO2 + 2e-

Question 4

Characteristics of manganate and ethanedioic acid reaction

Answer 4

Very slow so the ethanedioic acid is usually heated to about 60c

Question 5

What are Mn2+ ions?

Answer 5

Catalyse the reaction so they’re self-catalysis as the more of then the faster the reaction

Question 6

Equations for reaction of iodine and thiosulfate

Answer 6

2S2O3 2- –> S4O6 2- + 2e-

I2 + 2e- –> 2I-

Question 7

Colour change between iodine and thiosulfate?

Answer 7

Thiosulfate is colourless and iodine is brown.

Both products are colourless

Question 8

Reduction of chlorate (I) ions

Answer 8

ClO- + 2H+ + 2e- –> Cl- + H2O

Question 9

How to determine the strength of a bleach solution?

Answer 9

Chlorate (I) ions are reacted with excess iodide ions I- in acidic solution.
Iodine is produced which is yellow-brown.
Determine the quantity of iodine produced by back titrating with a standardised solution of Na2S2O3
Then work backwards to the conc of chlorate (I) ions

Question 10

How to find the conc of copper (II) ions?

Answer 10

Add excess KI to a known volume of a solution containing Cu2+ ions.
Copper (I) iodide is formed as a white precipitate and iodine.
Titrate the iodine with Na2S2O3.
Work backwards to the original conc