Topic 14- Redox II

Question 1

What conditions are assumed at the standard electrode potential?

Answer 1

1.0 mol dm-3
100kPa
298K/25c
No current flowing

Question 2

Reducing agent is itself …….

Answer 2

oxidised

Question 3

Oxidising agent is itself ……

Answer 3

reduced

Question 4

Why is a high resistance voltmeter needed?

Answer 4

To stop the current from flowing in the circuit so you can measure the maximum Potential Difference (E)

Question 5

What is the salt bridge soaked in?

Answer 5

filter paper soaked in KNO3, potassium nitrate

unreactive with electrodes and solutions

Question 6

The most positive electrode will always undergo ….

Answer 6

reduction

Question 7

the most negative electrode will always undergo …..

Answer 7

oxidation

Question 8

When writing cell diagrams, which species are put next to the double solid line?

Answer 8

The most oxidised (inside)

so then the outermost species are most reduced

Question 9

The more ……. half cell is written on the right

Answer 9

positive

Question 10

What do the lines represent in a cell diagram?

Answer 10

the salt bridge = I I

Separation of phases e.g. solid and solution = I

Question 11

What is a , used for in cell diagrams?

Answer 11

Separates species in the same physical state

Question 12

If a system doesn’t include a metal that can act as an electrode then a ….. electrode must be used.

Answer 12

platinum

Question 13

What is the reference electrode and what is its potential?

Answer 13

A hydrogen electrode and = 0v

Question 14

Why do we use a reference electrode?

Answer 14

As to measure the potential difference we need 2 electrodes and must know 1 potential

Question 15

The potential of all electrodes are measured by comparing their potential to that of the standard ….. electrode

Answer 15

hydrogen

Question 16

What is the equation for the hydrogen electrode equilibrium?

Answer 16

H2 2H+ + 2e-

Question 17

When writing half equations the more oxidised is on the ….. and the more reduced is therefore on the …..

Answer 17

The more oxidised = left

The more reduced = right

Question 18

in the electrode system containing two ………. it is necessary to use a platinum electrode and both solutions must be of a …. concentration.

Answer 18

solutions, 1 mol

Question 19

How to calculate the EMF of the cell?

Answer 19

Ecell= E(right) - E(left)
Ecell= E(reduction) - E(oxidation)

Question 20

The more …… electrode potential is on the right

Answer 20

positive

Question 21

The more ……. half cell will always reduce (go forwards)

Answer 21

positive

Question 22

How do you know which direction to write a half-cell equation in?

Answer 22

Reduction is always forward reaction (left to right) in half-cell equations, electrons always added on LEFT side

Question 23

Oxidation always happens at the….. and the reduction always happens at the ……

Answer 23

Oxidation = Anode
Reduction= Cathode

Question 24

More reactive metal gives up its electrons and is …. ( becomes the anode where e-‘s flow from) and less reactive metal becomes the cathode

Answer 24

More reactive metals become the anode and is oxidised

Question 25

When drawing half cells the half-cell where oxidation happens (the ……) should always be on the ……

Answer 25

Oxidation happens = anode = left

Question 26

When drawing half cells the half-cell where reduction happens ~( the cathode) should always be on the ….

Answer 26

Reduction happens = cathode = right

Question 27

What is the role of the salt bridge? (2)

Answer 27

The salt bridge completes the circuit (1)

and allows ions to flow between half cells to balance the charges (1)

Question 28

When calculating the electrode potential the half equation that is more positive E goes …… and the more negative …….

Answer 28

E goes forward if more positive

backwards if more negative

Question 29

Write an equation with the two half cells:
Zn(aq)2+ + 2e- = Zn(s) -0.76
Cu(aq)2+ + 2e- = Cu(s) +0.34

Answer 29

Cu2+ + Zn(s) == Cu(s) + Zn2+

Question 30

Define the standard electrode potential?

Answer 30

The voltage measured under standard conditions when the half-cell is connected to a standard hydrogen electrode

Question 31

The standard H electrode is always found on the ….. (in diagrams)

Answer 31

LEFT