Electrode potentials and electrochemical cells

Question 1

What happens when a rod of a metal is dipped into a solution of its own ions

Answer 1

An equilibrium is set up between the solid metal and the aqueous metal ions

Question 2

Write a half-equation for zinc (s) to zinc (II)

Answer 2

Zn (s) ⇋ Zn2+ (aq) + 2e-

Question 3

Write a half-equation for copper (II) to copper (III)

Answer 3

Cu2+ (aq) ⇋ Cu3+ (aq) +e-

Question 4

What is the simplest salt bridge made of?

Answer 4

Filter paper soaked in saturated solution of KNO3 (potassium nitrate)

Question 5

Why are salt bridges necessary

Answer 5

Complete the circuit, but avoid further metal/ion potentials as does not perform electrochemistry
Allows ion movement to balance the charge. Do not react with electrodes

Question 6

What symbol is used to represent a salt bridge in standard notation

Answer 6

||

Question 7

What type of species goes on the outside (furthest from the salt bridge) in standard cell notation

Answer 7

The most reduced species

Question 8

What does | indicate?

Answer 8

Phase boundary (Solid/liquid/gas)

Question 9

How would an Aluminium/Copper cell be represented?

Answer 9

Al (s) | Al3+ (aq) || Cu2+ (aq) | Cu (s)

Question 10

What happens at the left-hand electrode

Answer 10

Left hand electrode is where oxidation occurs
Left hand electrode is the half cell with the most negative E* value

Question 11

What happens at the right-hand electrode

Answer 11

Right electron is where reduction occurs
Right hand electrode is the half cell with the most positive E* value

Question 12

Which side of the cell has the most negative E* value? What happens to the metal with the most negative E* value?

Answer 12

Left hand electrode - Oxidation

Question 13

What conditions is the standard hydrogen electrode used in?

Answer 13

Temperature = 298K
Pressure = 100kPa
[H+] = 1.00 mol dm-3

Question 14

What is the standard hydrogen electrode used for?

Answer 14

Comparing other cells against. E* of SHE is defined as 0, so all E* values are compared against it

Question 15

Why might you use other standard electrodes occaisionally

Answer 15

They are cheaper/easier/quicker to use and can provide just as good a reference
Platinum is expensive

Question 16

If an E* value is more negative, what does it mean in terms of oxidising / reducing power?

Answer 16

Better reducing agent (easier to oxidise)

Question 17

If an E* value is more positive, what does it mean in terms of oxidising/reducing power?

Answer 17

Better oxidising agent (easier to reduce)

Question 18

What factors will change E* values

Answer 18

Concentration of ions
Temperature

Question 19

What happens if you reduce the concentration of the ions in the left hand half cell

Answer 19

Equilibrium moves to the left to oppose the change of removing ions; the releases more electrons, the E* of the left hand cell becomes more negative, so the e.m.f. of the cell increases