Topic 14 Redox Equilibrium

Question 1

Steps to set up an electrochemical cell (5 steps)

Answer 1

1. Obtain and clean metal with sandpaper (+ gloves)
2. Clean grease from surface with propanone and wear gloves
3. Place each metal into a solution containing the ion of the same metal
   (Add acid for oxidising agents)
   4.Make salt bridge from filter paper and KNO3 (or KCl) and put it in each beaker not touching electrodes
4. Connect electrodes with wires and a voltmeter

Question 2

What are the two types of half cell

Answer 2

Metal electrode in its own ions or platinum electrode with 2 aqueous ions

Question 3

Why is a platinum electrode used for solutions containing two aqueous ions

Answer 3

Inert and conductive

Question 4

Where do electrons flow from and to in terms of reactivity

Answer 4

From a more reactive metal to a less reactive metal

Question 5

What is electrode potential

Answer 5

How easily half cells give up electrons (are oxidised)

Question 6

What does NO PRoblem stand for

Answer 6

Most Negative half cell is Oxidised
Most Positive half cell is Reduced

Question 7

What is the SHE and what is it used for

Answer 7

Standard hydrogen electrode. Used as a reference to measure standard electrode potentials

Question 8

What is the set up of the SHE

Answer 8

Pt electrode, 1 mol dm-3 H+ and H2(g) in at 298K, 100 kPa

Question 9

3 Standard conditions of SHE?

Answer 9

1. 298K
2. 100kPa
3. 1 mol dm^-3 conc H+

Question 10

Formula for standard cell potential

Answer 10

E reduced - E oxidised
E right - E left
E most positive - E most negative

Question 11

3 things affecting half cell potential

Answer 11

1. Temp
2. Conc
3. Pressure

Question 12

Cell notation acronym

Answer 12

ROOR - R - reduced state O - oxidised state

Question 13

Cell notation rules (4)

Answer 13

1. Negative half cell left positive right
2. Reduced form Oxidised form Oxidised form Reduced form
3. Single line for state change double line for salt bridge
4. Comma to separate substances in same state (don’t forget Pt electrode)

Question 14

When is a reaction feasible in electrochemical cells

Answer 14

E cell > 0 or do NO PRoblem and see if the equation formed matches the question

Question 15

When may a feasible reaction not occur (3)

Answer 15

• non standard conditions
• slow rate of reaction
• activation energy too high

Question 16

What is E cell directly proportional to

Answer 16

Total entropy change and the natural log of the equilibrium constant (lnk)

Question 17

How do rechargeable batteries work

Answer 17

When a current is supplied the discharge equation is reversed

Question 18

What two substances react in a lithium ion battery

Answer 18

Lithium and Cobalt (IV) Dioxide

Question 19

What do fuel cells need to generate electricity

Answer 19

A continuous external supply of chemicals

Question 20

Ox and Red Formula in alkaline hydrogen fuel cell

Answer 20

OX 2H2 + 4OH- —> 4H2O + 4e-
RED O2 + 2H2O + 4e- —> 4OH-

Question 21

General formula for hydrogen fuel cells

Answer 21

O2 + 2H2 —> 2H2O

Question 22

Electrolyte in alkaline fuel cells

Answer 22

KOH to carry OH-

Question 23

Two other hydrogen rich molecules used in fuel cells? And how do they create hydrogen from them

Answer 23

Methanol and ethanol release hydrogen using a reformer

Question 24

Why is a salt bridge used

Answer 24

To complete the circuit and balance charges

Question 25

What are redox titrations used for

Answer 25

To find the concentration of a reducing or oxidising agent

Question 26

When should you add starch to titrations involving iodine

Answer 26

When most of the iodine has reacted otherwise the blue black colour takes too long to diseappear