# Quiz | Electrochemistry

1

Which of the following statements is incorrect?

Reduction occurs at the cathode

All electrochemical reactions involve the transfer of electrons

It is possible to directly measure the voltage of a single electrode

Electrolysis is a technique that uses electric current to drive an otherwise non-spontaneous chemical reaction

It is not possible to directly measure the voltage of a single electrode but it can be determined by measuring the voltage difference between a standard electrode and the desired electrode ⇒ in electrochemistry, a Standard Hydrogen Electrode (SHE) is used

2

Which of the following statement about salt bridge is correct?

It is an agar gel through which ions cannot pass

It allows charge balance to be maintained in the cell

It is represented by a single vertical bar in a cell diagram

It drives free electrons from one electrode to the other

Salt bridge provides an ionic current path between the 2 solutions with electrodes in order to maintain the charge balance in the cell

3

Why is Standard Hydrogen Electrode (SHE) called as the primary reference electrode?

Its voltage E0 = 0 V

The electrode is a nonreactive metal

Its output potential is independent of the composition of the solution

All of the above

By convention, the voltage of the SHE is E0 = 0 V ⇒ SHE is the primary reference electrode
2 H+ (aq) + 2 e- → H2 (g)     [E0red = 0 V]

4

What is the reaction of the zinc-copper cell: Zn (s) | ZnSO4(aq) || CuSO4(aq) | Cu(s)?

ZnSO(aq) → Zn2+ (aq) + 2 SO4- (aq)

Zn (s) + Cu2+ (aq) → Cu (s) + Zn2+ (aq)

Cu (s) + Zn2+ (aq) → Zn (s) + Cu2+ (aq)

Cu (s) + ZnSO(aq) → Zn (s) + CuSO(aq)

By convention:
- left-hand electrode: oxidation reaction ⇒ Zn (s) → Zn2+ (aq) + 2 e-
- right-hand electrode: reduction reaction ⇒ Cu2+ (aq) + 2 e- → Cu (s)

5

What is the half-reaction that occurs at the anode during the electrolysis of sodium bromide?

Na+ + e- → Na

Na → Na+ + e-

Br2 + 2 e- → 2 Br-

2 Br- → Br2 + 2 e-

Electrolysis of NaBr: 2 Br- (aq) + 2 Na+ (aq) → Br2 (l) + 2 Na (s)
Anode: oxidation reaction ⇒ 2 Br- → Br2 + 2 e-

6

What is the correct Nernst equation for the reaction: Cu (s) + Zn2+ (aq) → Zn (s) + Cu2+ (aq)?

E = E0 + RT/2F x ln Q

E = E0 – RT/2F x ln Q

E = E0 + RT/F x ln Q

E = E0 – RT/F x ln Q

Nernst equation: E = E0  –  $\frac{\mathrm{RT}}{{\mathrm{\nu }}_{\mathrm{e}}\mathrm{F}}$  ln Q

Cu (s) + Zn2+ (aq) → Zn (s) + Cu2+ (aq) can be broken down into 2 half reaction equations:
Cu (s) → 2 e- + Cu2+ (aq) and Zn2+ (aq) + 2 e- → Zn (s)
⇒ stoichiometric coefficient of the electrons in the 2 half reaction equations νe = 2