Redox 2

Question 1

Describe a method to set up an electrochemical cell.

Answer 1

• Obtain metals that are cleaned with sandpaper (to ensure impurities are removed)
• wash surface of the metal with propanone and wear gloves (so no hand grease gets on the metal)
• Place each metal into a solution containing the ion of the same metal
• Make salt bridge from filter paper (soaked filter paper in Potassium Nitrate)
• connect electrodes with Voltmeter, crocodile clips and wires to measure potential difference.

Question 2

Describe 2 methods to construct a half cell

Answer 2

• metal dipped into a solution of its ions
• or platinum electrode with 2 aqueous ions.

Question 3

Describe the movement of electrons in an electrochemical cell

Answer 3

• flow from a more reactive to less reactive metal.

Question 4

What is the function of the salt bridge?

Answer 4

• Ensures charges are balanced on either side of the electrochemical cells.

Question 5

How can you tell which electrode is going through oxidation and which one is going through reduction?

Answer 5

• one with the most negative cell value is where oxidation takes place.
• one with the most positive value is where reduction takes place.

Question 6

What is a standard hydrogen electrode?

Answer 6

• a electrode that is used as a reference to measure E0 values.

Question 7

What conditions must be met for a reading to show up in the voltmeter when a metal is connected to the SHE?

Answer 7

• standard conditions of :
• 298K
• 100kPa
• 1moldm^-3 concentrations of ions.

Question 8

How can you tell is a cell is a strong oxidising agent?

Answer 8

• from the left side of the equation going down in the electrochemical series.
• So more likely to be reduced (to gain electrons)

Question 9

How can you tell is a cell is a strong reducing agent?

Answer 9

• from the right hand side of the equation going up in the electrochemical series
• so more likely to be oxidised (to loose electrons)

Question 10

How do you calculate the standard cell potential?

Answer 10

• E0reduced - Eoxidised

Question 11

Quicker way to tell what half cell is being oxidised and reduced

Answer 11

• most negative E0 value= oxidised (so best reducing agent)
• most positive E0 value = reduced.(so better oxidising agent)

Question 12

What factors affect half cells?

Answer 12

• temp
• conc
• pressure

Question 13

What is the cell notation form?

Answer 13

• reduced form (electrode) I electrode (oxidised form) II Oxidised form I reduced form

Question 14

How to predict if a reaction will be feasible?

Answer 14

• E0 calculation will have a positive value

Question 15

What may cause the electrode potentials to change?

Answer 15

• change in concentration or temperature

Question 16

What might make a reaction kinetically unfavourable?

Answer 16

• if the activation energy is too high
• if the rate of reaction is extremely slow.

Question 17

What is the link between entropy and cell potential?

Answer 17

• the larger the cell potential, the larger the total entropy change during the cell reaction
• so E0 is proportional to ΔStotal

Question 18

What is the link between entropy and the equilibrium constant?

Answer 18

• E0 is proportional to lnK

Question 19

What is a fuel cell?

Answer 19

• uses the energy from the reaction of a fuel with oxygen to create a voltage

Question 20

Give the half equation for the reaction at the anode in a fuel cell

Answer 20

2H2 + 4OH- —> 4H20 + 4e-