11: Electrochemical cells and electrode potentials

Question 1

What is the connection between the two solutions called

Answer 1

The salt bridge

Question 2

What is the purpose of a salt bridge

Answer 2

Allows movement of ions between the two solutions

No electrons are transferred through the salt bridge

Question 3

How can a simple salt bridge be made

Answer 3

Piece of filter paper soaked in saturated potassium nitrate solution

Question 4

Which electrode does reduction happen at

Answer 4

Positive electrode

Reduction

At

Positive

Question 5

Which electrode does oxidation happen at

Answer 5

The negative electrode

Question 6

What is the potential difference measured in the cell called

Answer 6

Cell potential

Question 7

What is used when an electrode cant be made (i.e.. the half cell reaction is only between gases and/or aq)

Answer 7

Platinum

Question 8

How does a standard hydrogen electrode work

Answer 8

Hydrogen gas is bubbled over a platinum electrode. The platinum is almost entirely unreactive so does not interfere with the chemistry, but conducts the electrons and forms a catalytic surface on which the hydrogen gas can be in contact with the hydrogen ions.

Question 9

What is the half equation for the hydrogen electrode

Answer 9

H†(aq) + e¯ ⇌ ½H₂(g)

Question 10

What are standard conditions for any half cell

Answer 10

Temperature: 298K (25℃)

Solutions at 1.00 moldm¯³

Gases at 1 atmosphere pressure

Question 11

What is the standard electrode potential (Eϴ) of a half cell

Answer 11

The voltage measured in a cell in which that half cell is connected to a standard hydrogen electrode, under standard conditions

Question 12

What does a very positive Eϴ mean

Answer 12

Reduction will occur readily at the electrode

Question 13

What does a very negative Eϴ mean

Answer 13

Oxidation occurs readily at this electrode

Question 14

How does a metal’s reactivity affect its Eϴ

Answer 14

The more reactive a metal is, the less favourable reduction of its ions will be and the more negative the Eϴ will be

Question 15

How set up half cell for gases and ions

Answer 15

Bubble gas over platinum electrode and immerse it in a solution of the ions formed by the oxidation or reduction of the gas

Question 16

How to set up half cell for ions in solution

Answer 16

submerge platinum electrode in solution containing the ions

Question 17

What is standard cell potential (Eϴ cell)

Answer 17

It is equal to the difference between the Eϴ values

Always expressed as a positive value

Question 18

How do you know which half reaction will oxidise and which will reduce

Answer 18

The half reaction with the more positive value for Eϴ will reduce

Question 19

How can you work out what effect a change in conditions will have on electrode potentials

Answer 19

Using Le Chatelier’s principles

Question 20

What happens to the electrode potential in the half cell Zn²†(aq) + 2e¯ ⇌ Zn(s) when the concentration of Zn²† is increased

Answer 20

The equilibrium will move to the right to compensate so reduction is now favoured so the electrode potential will become more positive

Question 21

How close do the Eϴ values have to be so that when it is not standard conditions, you can not reliably predict the direction of reaction

Answer 21

Within about 0.3V

Question 22

What is a storage cell

Answer 22

An electrochemical cell where the voltmeter can be replaced by an electrically powered device (e.g. a light bulb) and energy released by the cell reaction is used to create a voltage for the device

Question 23

What is a fuel cell

Answer 23

An electrochemical cell which uses the energy released by the reaction of a fuel with oxygen to generate a voltage

Question 24

How does a fuel cell differ from a storage cell

Answer 24

It is not a closed system

Question 25

How does a fuel cell work

Answer 25

A continuous supply of fuel (such as hydrogen or an organic compound) is delivered to the negative electrode to be oxidised whilst a continuous supply of oxygen (usually air) is delivered to the positive electrode to be reduced