Redox + Electrochemistry

Question 1

What is an oxidising agent?

Answer 1

• substance that oxidises another atom or ion by causing it to lose e^-, + is itself reduced (gains e^-) in the process so it’s ox. no. dec.

Question 2

What is a reducing agent?

Answer 2

• substance that reduces another atom or ion by causing it to gain e^-, + is itself oxidised (loses e^-) in the process so it’s ox. no. inc.

Question 3

What is a redox reaction?

Answer 3

• reaction where there is both an oxidising + reducing agent

Question 4

How do you balance a redox equation?

Answer 4

• write unbalanced equation + identify atoms which change in ox. state
• deduce ox. state changes
• balance ox. state changes
• balance charges
• balance atoms

Question 5

What atoms are normally used to balance redox equations?

Answer 5

• H+
• OH-
• H2O

Question 6

What are the 2 common redox titrations?

Answer 6

• manganate (VII) titrations
• iodine-thiosulfate titrations

Question 7

In a manganate (VII) titration what is usually used to acidify the reaction mixture + why?

Answer 7

• dilute sulfuric acid bc doesn’t react w manganate ions + is not oxidised under these conditions

Question 8

What is the colour of the end point in a manganate titration?

Answer 8

• pale pink bc there’s a low conc of excess Mn2+ ions (purple)

Question 9

What is the equation for the redox reaction between iodine + thiosulfate ions?

Answer 9

2S₂O₃^2- + I₂ ——> 2I^- + S₄O₆^2-

Question 10

What is the colour change observed at the start of an iodine-thiosulfate titration?

Answer 10

• brown/yellow to pale yellow as the iodine gets reduced to iodide ions (I-)

Question 11

What is added to the pale yellow reaction mixture in an iodine+thiosulfate titration + why?

Answer 11

• starch, which turns the solution blue black so makes the end point more obvious

Question 12

What is the colour of the end point in a iodine-thiosulfate titration?

Answer 12

• colourless