PAG 8 - Electrochemical cells

Question 1

What must a half cell contain?

Answer 1

An element in 2 oxidation states

Question 2

Define the terms oxidation and reduction

Answer 2

Oxidation - loss of electrons
Reduction - gain of electrons

(oil rig)

Question 3

Why must metal electrodes be cleaned
with sandpaper before creating an
electrochemical cell?

Answer 3

To remove any metal oxide that has
formed on the surface and improve
electrical conductivity.

Question 4

Describe the movement of electrons in

an electrochemical cell

Answer 4

Electrons flow through the wire from the
positive electrode to the negative
electrode.

Question 5

In an standard Zn/Zn2+ cell, what is the

role of potassium nitrate solution?

Answer 5

Potassium nitrate is used to saturate a
piece of filter paper so that it can be
used as a salt bridge

Question 6

Why is a salt bridge used in an

electrochemical cell?

Answer 6

To maintain the charge balance and complete the circuit.
This is because negative electrons are moving from one
half cell to another. Without the salt bridge, positive charge
would build up in the half cell containing the anode and
negative charge would build up in the half cell containing
the cathode. This would cause the reaction to stop

Question 7

Why must an inert salt be used in the

salt bridge?

Answer 7

So that the salt doesn’t react with the
solutions and alter their concentrations. If
a reactive salt was used, the cell
potential would change.

Question 8

What moves across the salt bridge?

Answer 8

Ions

Question 9

In an electrochemical cell, each metal
electrode is placed in a solution
containing what?

Answer 9

Its ions
E.g. solid copper is placed in a solution
of copper(II) sulfate

Question 10

Standard conditions are often used when
investigating electrochemical cells. What
are the standard conditions?

Answer 10

1 mol dm-3 solutions
298 K
1 atm

Question 11

After setting up an electrochemical cell,
the reading on the voltmeter is negative.
What should be done?

Answer 11

Switch the connection of the wires so the

electrodes are the right way round

Question 12

What is the formula for the electromotive

force (EMF)?

Answer 12

EMF = E(R) − E(L)

where E(R)
 - right-hand cell, 
where reduction occurs, 
and E(L)
 - left-hand cell,
where oxidation occurs.

Question 13

For a reaction to be thermodynamically
feasible, what must the value of the EMF
be?

Answer 13

Positive