5.2.3 Redox

Question 1

What is oxidation?

Answer 1

• the loss of electrons

Question 2

What is reduction?

Answer 2

• the gain of electrons

Question 3

What blocks undergo reduction and oxidation?

Answer 3

• s, d and some p block elements undergo oxidation
• most p block elements undergo reduction

Question 4

What happens in the titration between iron and manganate?

Answer 4

• iron ions are oxidised while manganate ions are reduced
• the end is when the manganate is a pale pink (at this point there is an excess of manganate ions)

Question 5

What is the overall reaction for a manganate titration?

Answer 5

MnO4- +8H+ + 5Fe2+ -> Mn2+ + 5Fe3+ +4H2O

Question 6

What happens in the titration between iodine and thiosulphate?

Answer 6

• thiosulphate ions are oxidised and iodine is reduced
• it is a clock reaction so the end point goes from blue-black to colourless (adding starch part way)

Question 7

What is the overall reaction for thiosulphate titrations?

Answer 7

2S2O32- + I2 -> S4O62- + 2I-

Question 8

What is the equation for chromium?

Answer 8

Cr2O72- +14H+ + 6e- —> 2Cr3+ + 7H2O