Chapter 4 - Electrolysis

Question 1

What does an electrolytic cell do?

Answer 1

Turns electrical energy into chemical energy.

Question 2

Why do the substances in an electrolytic cell not have to be separated?

Answer 2

Because they are non-spontaneous reactions and therefore won’t react by themselves.

Question 3

when drawing a power pack the positive electrode connects to the

Answer 3

larger stick

Question 4

when drawing a power pack the negative electrode connects to the

Answer 4

smaller stick

Question 5

ALWAYS

anions are attracted to the

Answer 5

anode

Question 6

ALWAYS

cations are attracted to the

Answer 6

cathode

Question 7

how do we predict which reaction will occur?

Answer 7

We first circle the possible reacting species. If something is not in the P.R.S we cannot circle that side of the equation.

Then We look at the electrochemical series and pick the highest on the left and lowest on the right.

We draw a line to check if it is galvanic or electrolytic.

Question 8

What is electroplating?

Answer 8

Where an object is used as the cathode in an electrolytic cell and is plated with metal ions undergoing reduction.

Question 9

GOLDEN RULE OF ELECTROLYTIC CELLS

Answer 9

THE CATHODE CAN NEVER TAKE PART IN A REACTION AS ELECTRONS ARE BEING FORCED ONTO IT AND THUS IT ALWAYS UNDERGOES REDUCTION.

Question 10

What is faraday’s first law

Answer 10

electric charge depends on current and time

Q=It

Q is electric charge in coulombs
I is current in amperes
t is time in seconds

Question 11

What is faraday’s second law

Answer 11

charge on an ion can be calculated from electric charge.

n(e-) = Q/F

F is faradays constant = 96500

Question 12

Relationship between a faraday and a mole of electrons

Answer 12

1 faraday = 1 mole of electrons

Question 13

What is a discharge reaction

Answer 13

this is a galvanic reaction that occurs in a secondary cell. The discharge is the products formed. The discharge must stay in contact with the electrodes for a cell to be recharged.

Question 14

What is a recharge reaction

Answer 14

this is an electrolytic reaction that occurs in a secondary cell. The discharge products are converted back into the original reactants.

Question 15

How to find the discharge and recharge equation

Answer 15

First we find one and then the other is just the same equation but flipped

Question 16

Describe the electrolysis of Brine

Answer 16

A high concentrated solution of NaCl can change the order of the electrochemical series. It allows Cl- to be a prefer reductant and so Cl- reacts with water to produce Cl2, H2 and OH-. Once all of the solution has been electrolysed, Na is left behind. it passes through the semi-permeable membrane and forms NaOH.

Question 17

What does a semi-permeable membrane do?

Answer 17

Isolates electrodes.

Question 18

Why does a brine solution need a semi-permeable membrane?

Answer 18

As the products formed at each electrode, Na+ and Cl- could come together and form NaCl in an explosive manner.

Question 19

When asking about why this salt bridge could not be used, we look for…

Answer 19

If the ions would be preferably oxidised or reduced rather than the originally intended reactants.

If a precipitate will form with another reactant.