Electrolysis

Question 1

Definition of an electrolyte

Answer 1

The substance broken down by electrolysis is called an electrolyte. Electrolytes are made up of ions

Question 2

Why can’t solid ionic compounds conduct electricity?

Answer 2

The ions are fixed in a giant lattice so are unable to freely move to its oppositely charged electrode.

Question 3

Why can ionic compounds that are molten or aqueous form able to conduct electricity?

Answer 3

The ions are free to move in the giant lattice to their oppositely charged electrode

Question 4

Which compounds will undergo electrolysis?

Answer 4

Ionic compounds will undergo electrolysis because it is made of ions which can carry charge. Has to be in molten or aqueous form so the ions are free to move to their oppositely charged electrode

Question 5

How is electrolysis set up

Answer 5

Two electrodes that are connected to a power supply are dipped into the electrolyte

Question 6

What is an electrode

Answer 6

A material which carries an electrical current

Question 7

Why are electrodes often made of graphite

2 reasons

Answer 7

• conducts electricity

- unreactive (doesn’t react with electrolyte)

Question 8

Which ions are attracted to which electrode

Answer 8

Positive cations attract to the negative cathode

Negative anions attract to the positive anode

Question 9

What mnemonic helps to remember the names of electrodes and what does it stand for?

Answer 9

PANIC

Positive Anode Negative is Cathode

Question 10

What is an oxidation reaction? How do we remember this?

Answer 10

Loss of electrons

OIL - Oxidation Is Loss

Question 11

What is a reduction reaction? How do we remember this?

Answer 11

Gain of electrons

RIG - Reduction Is Gain

Question 12

What happens when ions reach their oppositely charged electrode?

Answer 12

The ions lose their charge (discharged) and become elements/ atoms.

Question 13

Which electrode does oxidation occur and why?

Answer 13

Positive anode

Oxidation is the loss of electrons which means the ions were negative as they had more electrons. The negative anions attract to the positive anode.

Question 14

Which electrode does reduction occur and why?

Answer 14

Negative cathode

Reduction is the gain of electrons which means the ions were positive as they had less electrons. The positive cations attract to the negative cathode

Question 15

What happens to the electrons lost at the anode?

Answer 15

The electrons flow around the circuit to the cathode

Question 16

Definition of electrolysis

Answer 16

A process that uses an electric current to split up a substance that contains ions

Question 17

What happens at the anode?

Answer 17

The negative ions are attracted to the positive anode. Each ion has to lose (e.g. 1) electron to become neutral. This is an oxidation reaction. Forms the atom/ element.

Question 18

What happens at the cathode?

Answer 18

The positive ions are attracted to the negative cathode. Each ion has to gain (e.g. 1) electron to become neutral. This is a reduction reaction. Forms the atom/ element

Question 19

Example of the equation at the anode with sodium chloride. What type of reaction?

Answer 19

2Cl- —–> Cl2 + 2e-

Oxidation

Question 20

Example of the equation at the cathode with sodium chloride. What type of reaction?

Answer 20

Na+ + e- ——> Na

Reduction

Question 21

Why is it sometimes easier to electrolyse the aqueous solution?

Answer 21

Most ionic compounds have high melting points do it is difficult to melt them and make then molten. It is easier to dissolve them in water and electrolyse the aqueous solution

Question 22

What ions will be present in a solution

Answer 22

H2O —-> H+ + OH-

Question 23

What apparatus do we use for the electrolysis of water?

Answer 23

Hoffmann Voltameter

Question 24

What happens at the cathode for the electrolysis of water?

Equation?

Answer 24

H+ ions are attracted
Gains 1 electron
Reduction reaction

2H+ + 2e- —–> H2

Question 25

What happens at the anode for the electrolysis of water? | Equation?

Answer 25

OH- ions are attracted Loses 1 electron Oxidation 4OH- -----> O2 + 2H2O + 4e-

Question 26

Predicting products at the cathode?

Answer 26

Least reactive positive ions are formed | Metals lower than hydrogen in the reactivity series will go to the cathode

Question 27

Predicting products at the anode?

Answer 27

Negative ions are attracted If a halide ion is present a halogen is formed Otherwise, OH- ions go to the anode and form oxygen

Question 28

What are the four ions present in brine solution?

Answer 28

Na+ Cl- H+ OH-

Question 29

What colour is the universal indicator for brine and what does it mean?

Answer 29

Green, neutral

Question 30

What ions will move to the cathode for brine and why?

Answer 30

H+ ions | Less reactive than Na+

Question 31

What is the product of brine at the cathode? What is the equation? How can we confirm the product?

Answer 31

H2 2H+(aq) + 2e- -----> H2(g) Squeaky pop test - lighted splint into the gas, if it pops there is hydrogen present

Question 32

What ions will move to the anode for brine and why?

Answer 32

Cl- ions | Halide ion present

Question 33

What is the product of brine at the anode? What is the equation? How can we confirm the product?

Answer 33

Cl2 2Cl(aq) -----> Cl2(g) + 2e- Blue litmus paper becomes pink then bleaches

Question 34

How does the colour of the universal indicator change at the anode for brine? What does it mean?

Answer 34

Starts green and changes to yellow (acidic). Then it turns colourless because chlorine is a bleach. Chlorine is produced at the anode

Question 35

What colour is the universal indicator for the remaining solution of brine? What does it mean? What is the solution?

Answer 35

Purple ---> alkaline OH- ions are alkaline Forms NaOH(aq)

Question 36

Equation for electrolysis for Brine

Answer 36

2NaCl + 2H2O -----> H2 + Cl2 + 2NaOH

Question 37

Uses of products of electrolysis of brine

Answer 37

Chlorine- kills bacteria in swimming pools, bleach Hydrogen- fuel, used to make margarine Sodium hydroxide- soap, paper

Question 38

What is electroplating?

Answer 38

An electroplated object is one that is coated with a thin layer of metal by the process of electrolysis

Question 39

Uses if electroplated objects 4 reasons

Answer 39

Protect metal underneath from corroding Looks more attractive Increase hardness or resistance to scratching Saves money by using a thin layer of precious metal

Question 40

What is the anode for electroplating and what happens what reaction?

Answer 40

The anode is always the plating material | Oxidation - loses electrons to become positively charged

Question 41

What is the cathode for electroplating and what happens what reaction?

Answer 41

The cathode is always the object that will be plated | Reduction - gains electrons to become negatively charged

Question 42

What safety precaution should be taken if something is toxic

Answer 42

Do the experiment in the fine cupboard

Question 43

How could a sample of gas be collected at the positive electrode be collected?

Answer 43

Collect the gas using displacement of the electrolyte in a test tube

Question 44

Why might hydrogen gas be produced at the cathode?

Answer 44

Hydrogen ions are positive Opposite charges attract Less reactive than the other metal