14.1.3 - The standard hydrogen electrode

Question 1

What are standard conditions for electrochemical cell measurements?

Answer 1

298K
100KPa
solutions at a concentration of one mole dm^-3

Question 2

What is the cell diagram for the reaction in an electrochemical cell between copper sulfate and zinc?

Answer 2

Zn(s)|Zn^2+(aq)||Cu^2+(aq)|Cu(s)

(the double line in the middle should be dashed as it represents the salt bridge

Question 3

What happens if the e.m.f is positive in relation to the cell diagram?

Answer 3

The reaction goes as shown, from left to right

Question 4

Why is a standard hydrogen electrode used?

Answer 4

The e.m.f of a single electrode cannot be measured directly so it’s measured against a reference electrode, which is the reference electode.

Question 5

What metal wire is used inside the hydrogen electrode?

Answer 5

Platinum wire

Question 6

What pressure doe the hydrogen gas enter the standard hydrogen electrode at?

Answer 6

100Kpa

Question 7

What type of acid is used when a standard hydrogen electrode is used?

Answer 7

Hydrochloric acid

Question 8

How is a cell diagram written with a standard hydrogen electrode?

Answer 8

Hydrogen always on the left side
Platinum is just before hydrogen

Question 9

If the e.m.f for zinc with a hydrogen electrode is negative what does this mean?

Answer 9

Electrons flow from the zinc electrode to the hydrogen electrode, in the opposite direction to the cell diagram.

Question 10

Why is the platinum foil at the bottom of the hydrogen electrode covered in porous platinum?

Answer 10

Porous platinum has a large surface area and allows equilibrium between hydrogen ions in solution and hydrogen gas to be established quickly.