Electrolysis

Question 1

Electrolysis means ….

Answer 1

when you pass an electric current through a molten or dissolved ionic substance

Question 2

What happens when you pass an electric current through a molten ionic substance or an ionic solution?

Answer 2

The solution breaks down into the elements it’s made of.

Question 3

What does electrolysis require?

Answer 3

A liquid to conduct the electricity, called electrolyte

Question 4

What do electrolytes contain?

What do these do?

Answer 4

Free ions usually in the molten or dissolved ionic substance

Conduct the electricity

Question 5

For an electrical circuit to be complete there has to be what?
So electrons are taken away from where?
Where are they given to?
As ions gain or lose electrons what happens to them?

Answer 5

A flow of electrons
The negative electrode, cathode
Positive electrode, anode
They become atoms or molecules and are released

Question 6

Reduction is …

So in electrolysis reduction is the …. of …

Answer 6

gain

gain of electrons

Question 7

Oxidation is …

So in electrolysis oxidation is the …. of …

Answer 7

loss

loss of electrons

Question 8

Electrolysis always involves either what or what?

Answer 8

Oxidation or reduction

Question 9

What happens during the electrolysis of molten lead bromide?

1. What happens at the -ve electrode
2. What happens at the +ve electrode

Answer 9

1. At the -ve electrode one lead ion accepts two electrons and becomes one lead atom
2. Two bromide ions lose one electron each and become one bromide molecule, Br2

Question 10

…. ions are attracted to the -ve electrode. Here they … electrons
Lead is produced at the … electrode

Answer 10

+ve, gain

-ve

Question 11

…. ions are attracted to the +ve electrode. Here they … electrons
Bromine is produced at the … electrode

Answer 11

-ve, lose

+ve

Question 12

Reactivity does what in electrolysis? (simple)

Answer 12

affects the products formed by electrolysis

Question 13

Sometimes there are what in the electrolyte?
At the -ve electrode (cathode) where … ions gather because they have a …. charge, if there are … ions present the metals ions might do what? Why?

Answer 13

other free ions, like H+ ions and OH-.
metal, +ve, H+
Stay in the solution, because the H+ ions might be less reactive and so the reactive metal is more keen to stay as an ion. So Hydrogen will be produced unless the metal is less reactive.

Question 14

At the +ve electrode (anode) where … ions gather because they have a …. charge, if there are … ions and …. ions present the molecules of …, … or … might do what?
If none of these three or their group is present, what will form here?

Answer 14

-ve, -ve, OH- and halide ions
chlorine, bromine, iodine might form.
Oxygen

Question 15

What are the products of sodium chloride solution after electrolysis? (3)

Answer 15

Hydrogen, chlorine and sodium hydroxide

Question 16

What happens and is then produced at the -ve electrode during the electrolysis of sodium chloride solution?

Answer 16

Two hydrogen ions accept two electrons and become one hydrogen molecule

Question 17

What happens and is then produced at the +ve electrode during the electrolysis of sodium chloride solution?

Answer 17

Two chloride ions lose their electrons and become one chlorine molecule

Question 18

What happens to the sodium ions during the electrolysis of sodium chloride solution?

Answer 18

They stay in the solution because they are more reactive than hydrogen
Hydroxide ions from water are also left behind as H+ is produced at the anode. So the OH- join to the sodium to form NaOH in the solution

Question 19

Anode is where the …. goes as it is…. +ve

Cathode is where the … goes as it is…. -ve

Answer 19

non-metal

metal

Question 20

What do half equations show?
What are the half equations for sodium chloride?
Write the atom and what happens with the electrons and what the product is at 1. the -ve, then 2. the +ve

Answer 20

The reactions at the electrodes

1. 2H+ +2e- = H2
2. 2Cl- = Cl2 + 2e-

Question 21

What are the useful products from the electrolysis of sodium chloride solution?

Answer 21

1. Chlorine - production of bleach and plastics

2. Sodium hydroxide - a strong alkali used widely in the chemical industry, soap

Question 22

Aluminium is very …. but is always found naturally in ….
It’s main ore is …, after mining and purifying it … … is left
This is pure ….., what is the chemical formula for this?
How is it extracted?

Answer 22

abundant, compounds
white powder
Aluminium oxide, Al2O3
Electrolysis

Question 23

What is the melting point of aluminium oxide? So what’s the problem
What happens to the aluminium oxide instead?
So now the temperature it’s melted at has been reduced to … which is what and what?

Answer 23

Over 2000 degrees, melting it would be very expensive
It’s dissolved in molten cryolite (less common aluminum ore)
900 degrees, cheaper and easier to reach

Question 24

In the electrolysis of aluminium oxide what are the electrodes made of? Which is a ….

Answer 24

Carbon (graphite), good conductor of electricity

Question 25

``` What does the diagram of the electrolysis of aluminium oxide look like? The anode: The cathode: On top of the electrolyte, a layer of: Electrolyte layer: The product at the cathode layer: ```

Answer 25

Rods of graphite stick into the mixture, all connected with a positive charge. The positive electrode Carbon lining (graphite) of the vat has a negative charge as the cathode, the negative electrode ...crust Molten bauxite in cryolite A layer of molten aluminium

Question 26

What are the half equations for the electrolysis of aluminium?

Answer 26

``` N= Al3+ + 3e- = Al P= 2O2- = O2 + 4e- ```

Question 27

What forms at the cathode and the anode in the electrolysis of aluminium? What then is formed for one of them meaning what?

Answer 27

Cathode- aluminium Anode - oxygen The oxygen reacts with the carbon electrode to form CO2 meaning the positive electrode gradually gets eaten away, and now need to be replaced every now and again which is expensive

Question 28

What is electroplating and what does it do?

Answer 28

Uses electrolysis to coat the surface of one metal with another meta, e.g silver onto a brass cup for decoration

Question 29

What is the negative electrode when electroplating? What is the positive electrode when electroplating? What will the electrolyte contain? So what does that mean about the plating ions?

Answer 29

The metal object to be plated The pure metal that will be plating Ions of the plating metal The +ve electrode keeps the solution topped up, when the solution atoms are the ones to be plating the object

Question 30

Give an example of electroplating a brass cup with silver: What is the +ve electrode? What is the -ve electrode? What is the electrolyte?

Answer 30

Pure silver strip Brass cup Silver nitrate solution - Ag+, NO3 (-) little minus sign, lower sitting 3, not 3-

Question 31

What are the uses for electroplating? | 2 - examples and why

Answer 31

Decoration - silver is attarctive but very expensive so it's cheaper to coat a cup than make it solidly out of it, it looks the same (think about solid gold's properties) Conduction- metals like copper conduct electricity well so they are often used to plate metals for electronic circuits and computers