23.3 Iodine/thiosulfate redox titrations

Question 1

which species are involved in the iodine/thiosulfate titration?

Answer 1

S2O3 2-
I2

Question 2

what is oxidised in the iodine/thiosulfate titration?

Answer 2

S203 2-

Question 3

what is reduced in the iodine/thiosulfate titration?

Answer 3

I2

Question 4

what is the overall equation in the iodine/thiosulfate titration?

Answer 4

Question 5

what can iodine/thiosulfate titration be used for?

Answer 5

finding ClO- conc in bleach
finding Cu2+ conc

Question 6

how is an iodine/thiosulfate titration carried out?

Answer 6

1. add Na2S2O3 to burette
2. add the oxidising agent to conical flask
3. add potassium iodide to the oxidising agent which turns solution yellow-brown
4. carry out titration
5. add starch when the brown colour fades which causes the solution to go blue-black
6. end point is when blue-black dissapears

Question 7

why is starch added in a iodine/thiosulfate titration?

Answer 7

because it is easier to find the end-point

Question 8

how is a iodine/thiosulfate titration used to determine copper content of salts?

Answer 8

Cu2+ ions react with I- to form I2 and CuI

CuI = white
mixture = brown

then the I2 is titrated against sodium thiosulfate

by linking the equations, one mole of Cu2+ is the same as 1 mole of S2O3 2-

Question 9

ratio of S2O3 2- to I2

Answer 9

2 to 1

Question 10

ratio of S2O3 2- to Cu2+

Answer 10

1 to 1

Question 11

ratio of I2 to Cu2+

Answer 11

1 to 2