A8 - Redox

Question 1

Define oxidising agent

Answer 1

Removes electrons from another species by accepting them
Increasing species oxidation number

Question 2

Define reducing agent

Answer 2

Donates electrons to another species by loosing them
Decreasing the species oxidation number

Question 3

What is colour of manganate ion (MnO4-)

Answer 3

Purple

Question 4

Colour change for manganate redox titration

Answer 4

Colourless to pink

Question 5

What must be remebered when calculating a redox titration

Answer 5

Factor of x10

Question 6

Why is excess of KI added in first step of thiosulphate titration

Answer 6

Ensure all I2 is formed for the second titration

Question 7

What is the indicator used for a thiosulfate redox titration and what is result

Answer 7

Starch (add just before end point)
Colour change from blue-black to colourless

Question 8

When to add starch to indicate thiosulfate redox titration

Answer 8

Just before end point

Question 9

Define standard electrode potential

Answer 9

The potential difference of a half-cell, compared to a standard hydrogen half-cell
Under standard conditions (100kPa, 298K and all solutions at 1mol dm-3)

Question 10

What are standard conditions for half-cells

Answer 10

100 kPa
298 K
1mol dm-3

Question 11

Equation for calculating Ecell

Answer 11

more POSITIVE electode potential - more NEGATIVE electrode potential

Question 12

How is the reactant of fuel cells different to modern storage cells

Answer 12

Fuel cells reacts with oxygen to give electrical energy

Question 13

What is the limitation to using fuel cells

Answer 13

using hydrogen is dangerous, and hydrogen is explosive

Question 14

Why is using hydrogen in fuel cells dangerous

Answer 14

Hydrogen is explosive

Question 15

What is the advantage to modern fuel cells over fuel cells

Answer 15

Modern fuels (e.g ethanol) are easier to store + transport