Topic 14 - Redox II

Question 1

Describe the essential features of the standard hydrogen electrode

Answer 1

• H2 gas at 100Kpa
• 1.00 mol dm-3 H+(aq) ions at 298K
• Platinum electrode

Question 2

MnO4- + 8H + 5Fe2+ -> Mn2+ + 4H2O + 5Fe3+

What is the manganate (VII) acting as in this reaction?

Answer 2

-Oxidising agent

Question 3

What does emf stand for? What is it a measure of?

Answer 3

• Electromotive force

- Voltage

Question 4

Equation for the reaction in a standard hydrogen electrode

Answer 4

H+(aq) + e- ⇌ 1/2 H2(g)

Question 5

Why does E = 0 V for the standard hydrogen electrode?

Answer 5

-Because it is defined as 0 V

Question 6

Describe how you would measure the standard emf for a cell?

Answer 6

• Construct two half-cells
• Connect them using a salt bridge and external circuit
• Ensure standard conditions
• Measure potential using a high-resistance voltmeter

Question 7

Give the cell diagram for the standard hydrogen electrode

Answer 7

Hi+(aq)|H2(g)|Pt (s)

Question 8

Give the cell diagram for cell with half-cells of the standard hydrogen electrode and Mg2+ and a Mg electrode

Answer 8

Pt (s)|H2(g)|H+(aq) : : Mg2+(aq)|Mg(s)

Question 9

Equation for calculating E cell

Answer 9

E cell = E right - E left

Question 10

Why is an external electrical circuit needed in an electrochemical cell?

Answer 10

Connects the two electrodes, allowing electrons to flow from one half-cell to the other

Question 11

Why is a salt bridge needed in an electrochemical cell?

Answer 11

• Connects the two aqueous solutions, allowing ions to move between the two half-cells
• This reduces the chance of a precipitate forming

Question 12

What is potassium nitrate used in the salt bridge?

Answer 12

-Avoid precipitate forming with ions from the half-cells

Question 13

When is a reaction feasible?

Answer 13

When E cell is positive