TOPIC 14 REDOX II

Question 1

Why do we need a salt bridge in a cell ? 1

Answer 1

• Salt bridge= filter soaked in KNO3 (aq)

- So that ions can move between 2 solutions , without having mixed the two solutions .

Question 2

what are the standard conditions of the hydrogen electrode ? 3

Answer 2

• 298k
• 100kpa
• 1mol/dm^3

Question 3

half equation for hydrogen electrode? 1

Answer 3

H2 —-> 2e- + 2H+

Question 4

why is a high resistance voltmeter used in electrochemical cells ? 1

Answer 4

• so that no current flows hence we can measure the maximum voltage .

Question 5

how do we set up an electrochemical cell?

5

Answer 5

1- get strip of metal and clean with emery / sand paper
2-clean electrodes using bleach or propanone
3-place each electrode not a beaker of its ions (zn solid in zn aq solution )
4-salt bridge = immerse filter paper in potassium nitrate solution
5-connect electrodes to voltmeter using crocodile clips and wires.

Question 6

how do you calculate E cell ? 1

Answer 6

E RHS - E LHS ( so reduction - oxidation )

Question 7

what effects the electrode potentials ? 3

Answer 7

1- concentration
2- temperature
3- pressure

Question 8

which metal is oxidised ?1

Answer 8

most reactive metal ( so you write is first in cell diagram )

Question 9

how can you tell if a species is a strong oxidising agent ?

Answer 9

1- a more NEGATIVE ELECTRODE POTENTIAL MEANS THAT THE RHS substances are more easily oxidised .

Question 10

how can you tell if a species a strong reducing agent ? 1

Answer 10

A more POSITIVE ELECTRODE POTENTIAL MEAN THAT LHS is easily REDUCED .