Chapter 20 Electrochemistry

Question 1

Define standard electrode (reduction) potential

Answer 1

The voltage of a half-cell under standard conditions (ion concentration of 1.00 mol dm-3, 298K, 1atm), compared with a standard hydrogen electrode.

Question 2

Define standard cell potential

Answer 2

The difference in standard electrode potential between two specified half cells.

Question 3

Eθᶜᵉˡˡ= ?

Answer 3

Eθᶜᵉˡˡ=Eθᶜᵃᵗʰᵒᵈᵉ-Eθᵃⁿᵒᵈᵉ

Question 4

How to choose the Eθᶜᵃᵗʰᵒᵈᵉ?

Answer 4

Ionic equation with more positive Eθ voltage.

Question 5

How to choose the Eθᵃⁿᵒᵈᵉ?

Answer 5

Ionic equation with more negative Eθ voltage

Question 6

Cathode is the electrode where…

Answer 6

…reduction occurs.

Question 7

Anode is the electrode where…

Answer 7

…oxidation occurs.

Question 8

Cupric ion:

Answer 8

Cu¹⁺ ion.

Question 9

Ferrous ion:

Answer 9

Fe²⁺ ion.

Question 10

F= ?

Answer 10

F = Le. The Faraday constant, F, the Avogadro constant, L, and
the charge on the electron, e.

Question 11

Q= ?

Answer 11

Q = It. Q is the charge in coulombs, I is the current in amperes, t is the time in seconds.

Question 12

Nernst equation to find non-standard electrode potential:

Answer 12

E = E⦵ + [(0.059/z) x log[oxidised species]/[reduced species]]

Question 13

ΔG⦵= ? (kJmol⁻¹)

Answer 13

ΔG⦵= –nFE⦵cell/1000 (kJmol⁻¹)

Question 14

ΔG⦵= ? (Jmol⁻¹)

Answer 14

ΔG⦵= –nFE⦵cell (Jmol⁻¹)

Question 15

The standard hydrogen electrode (SHE):

Answer 15

The standard hydrogen electrode is a half-cell used as a reference electrode and consists of:
Hydrogen gas in equilibrium with H+ ions of concentration 1.00 mol dm-3 (at 1 atm).
2H+ (aq) + 2e- ⇌ H2 (g).
An inert platinum electrode that is in contact with the hydrogen gas and H+ ions.
When the standard hydrogen electrode is connected to another half-cell, the standard electrode potential of that half-cell can be read off a voltmeter.

Question 16

Steps of drawing standard electrode of gas+solution equilibria:

Answer 16

Standard hydrogen electrode connected to a voltmeter connected to a platinum electrode inside a bell glass with an opening for the gas to enter. The solution in a beaker should be in contact with the gas. Salt-bridge to connect the solution to the standard hydrogen electrode solution.

Question 17

Steps of drawing standard electrode of solution+solution equilibria:

Answer 17

Standard hydrogen electrode connected to a voltmeter connected to a platinum electrode. The two ions should be dissolved in solution in a beaker. Salt-bridge to connect the solution to the standard hydrogen electrode solution.

Question 18

Steps of drawing standard electrode of solid metal+solution equilibria:

Answer 18

Standard hydrogen electrode connected to a voltmeter connected to the solid metal electrode. The metal ions should be dissolved in solution in a beaker. Salt-bridge to connect the solution to the standard hydrogen electrode solution.

Question 19

During molten compound electrolysis what goes to cathode and anode?

Answer 19

Metal cation gets reduced at cathode and anion gets oxidised at anode.

Question 20

During aq solution electrolysis what species goes to cathode and gets reduced?

Answer 20

The positively charged cation with the most positive Eθ will be discharged at the cathode as this is the cation that is most easily reduced. (If the metal is below hydrogen in the reactivity series, the metal cation will get reduced and deposited. If metal is above hydrogen in the reactivity series, hydrogen ions will get reduced to H₂ gas.)

Question 21

During aq solution electrolysis what species goes to anode and gets oxidised?

Answer 21

The negatively charged anion with the most negative Eθ will be discharged at the anode, as this is the anion that is most easily oxidised. (If the solution contains concentrated halide ions, halide ions will get oxidised into halogens. If the solution contains dilute halide ions or any other anions, OH- will get oxidised to form H₂0 and O₂ gas.)