C6.1 - C6.4 Electrolysis✔️

Question 1

What is electrolysis?

Answer 1

Breaking down of an ionic compound through the uses of an electric current - the compound that is broken down is called the eletrolyte

Question 2

How do you set up an electrical circuit for electrolysis?

Answer 2

Two electrodes that dip into the electrolyte with gap in between them - electrodes are conducting rods - one is connected to the positive terminal of a power supply - positive electrode is the anode - other electrode is conected to the negative terminal - negative electrode is the cathode

Question 3

What are electrodes often made of? and why?

Answer 3

Electrodes often made of an unreactive metal ( or inert ) substance such as graphite - this is so electrodes do not react with the electrolytes or products made in electrolysis

Question 4

Describe the process during electrolysis?

Answer 4

During electrolysis positivley charged ions move to the cathode ( negative electrode ) at the same time negative ions move to the anode ( positive electrode ) , as opposite charges attract

Question 5

What happens to the ions when they reach the electrode?

Answer 5

When the ions reach the electrode they loose their charge and become elements - at the electrodes gases may be given off or metal deposited but it depends on the compound used and whether its molten or dissolved in water

Question 6

What is sometimes given of at the electrode? And what determines this?

Answer 6

Gasses may be given off at the electrodes as well as a build up of metal deposit - this depends on the compound used and wether it is molten or dissolved in water

Question 7

do ionic compounds conduct electric when they are solid?

Answer 7

No - ionic compounds do not conduct electric when solid as their ions are in fixed positions in their giant lattice - once melted (molten) ions are free to move and can carry their charge towards the electrodes

Question 8

Why is it difficult to predict what will be formend when electrolysing ionic compounds in a solution and not as molten compounds?

Answer 8

More difficult to predict what will be formend because water also forms ions - so products at each electrode are not always exactly what you would expect

Question 9

Can convalent compounds be electrolysed?

Answer 9

Cannot usually be electrolysed unless they react or ionise in water to form ions

Question 10

What happens to positive ions at the cathode

Answer 10

Positive charged ions gain electrons to become neutral atoms

Question 11

What happens to negative ions at the anode?

Answer 11

Negative charged ions loose electrons to become neutral atoms

Question 12

Gaining electrons is called …. ?

Answer 12

Reduction - ions are reduced

Question 13

Loosing electrons is called …. ?

Answer 13

Oxidation - ions are oxidised

Question 14

How do you repersent what is happening at each electrode?

Answer 14

Through the use of half equations

Question 15

What will be produced at the electrodes during electrolysis in aqeous solutions?

Answer 15

If two elements can be produced at an electrode the less reactive element either hydrogen or the metal will usually be produced at the cathode - at the anode oxygen gas is given off from discharged hydroxide ions produced from water or a halogen is produced if the electrolyte is a solution of a halide

Question 16

What is given of at the anode with electrolysis in an aqueous solution?

Answer 16

-oxygen gas given off - from discharged hydroxide ions produce from water

-a halogen is produced if the electrolyte is a solution of a halide

Question 17

What is the purpose of cryolight?

Answer 17

Cryolight is a minreal which lowers the melting point so it can be eletrolysed at 850 degrees
-makes it cheaper less energy used
-better for the enviorment

Question 18

Explain the process of the extraction of aluminium?

Answer 18

Bauxite mined from the ground and purified into aluminium oxide which is then mixed with molten cryolight (an ionic compound) and melted - molten aluminium oxide electrolysed which forms aluminium metal

Question 19

what happens at the anode when aluminium is electrolysed?

Answer 19

Oxygen 2- ions are attracted to the positive anode - and they transfer extra electrons - and are discharged as oxygen molecules which reactive with the carbon electrode - forms carbon dioxide

Question 20

what happens at the cathode when aluminium is electrolysed?

Answer 20

Electrons from the oxygen atoms pass through the wire to the negative cathode attracting AL 3+ ions and sharing 3 electrons forming aluminium atoms which then forms as molten aluminium metal at the bottom of the container

Question 21

What happens to oxygen and aluminium in terms or reduction and oxidation?

Answer 21

Oxygen ions oxidised - loses electrons
Aluminium ions reduced - gain electros

Question 22

What ions does water produce?

Answer 22

H+ ions and OH-

Question 23

Why does the carbon electrodes need to be replaced regulary for the electrolysis of molten aluminium?

Answer 23

The oxygen reacts with the hot carbon anodes making carbon dioxide gas which bubbles off removing carbon from the electrodes and wearing them down

Question 24

Word equation for the production of aluminium?

Answer 24

Aluminium oxide → aluminium + oxygen

Question 25

Symbol equation for production of alumnium?

Answer 25

2Al₂O₃ → 4AL + 3O₂

Question 26

What are the three products of the electrolysis of brine (concentrated chloride solution) ?

Answer 26

-chlorine gas - produced at the anode
-hydrogen gas - produced at the cathode
-sodium hydroxide solution is also formed

Question 27

Word equation for the electrolysis of brine?

Answer 27

Sodium chloride solution → hydrogen gas + chlorine gas + sodium hydroxide solution

Question 28

What happens at the anode during the electrolysis of brine?

Answer 28

Negative Cl- attracted to anode they loose one electron and are oxidised - they bond together in pairs and are given off as chlorine gas (CL₂)

Question 29

Half equation at the anode for electrolysis of brine?

Answer 29

2Cl- (aq) → Cl₂(g) + 2e-

Question 30

What happens at the cathode during the electrolysis of brine?

Answer 30

Positive hydrogen ions (H+) are attracted to negative electrode aswell as sodium ions (Na+) - so the less reactive element is discharged (hydorgen) so sodium ions stay in the solution as aqueous ions - When the H+ ions reach the electrode they gain one electron and are reduced and bond together in pairs and are given of as hydrogen gas (H₂)

Question 31

Half equation at the cathode for electrolysis of brine?

Answer 31

2H+(aq) + 2e- → H₂(g)

Question 32

How to test the solution produced during the electrolysis of brine is alkaline?

Answer 32

Test the solution around the cathode with and acid/base indicator because the solution only contain Na+ and OH- ions which is a solution of sodium hydroxide (as Cl- and H+ ions are removed during electrolysis)

Question 33

Why can carbon be used to dsiplace alumnium from its compound?

Answer 33

Carbond is less reactive then aluminium and only a more reactive element can displace a less reactive element

Question 34

Half equation at negative electrode in fuel cell?

Answer 34

2H₂ + 4OH- → 4H₂O + 4e-

Question 35

Half equation at positive electrode in fuel cell?

Answer 35

O₂ + 2H₂O + 4e- → 4OH-