C2- Salts and Electrolysis

Question 1

What is an alkali?

Answer 1

Alkalis are bases that dissolve in water to make alkaline solutions.

Question 2

What is a base?

Answer 2

Bases are substances that will neutralise acids.

Question 3

Which ions are produced by alkalis when dissolved in water?

Answer 3

Hydroxide ions, OH^-_(aq).

Question 4

What pH are acids?

Answer 4

Less than pH7.

Question 5

What pH are alkalis?

Answer 5

More than pH7.

Question 6

What is a neutralisation reaction?

Answer 6

When an acid reacts with a base to produce a salt and water. Acid + metal ➡️ A salt + hydrogen.

Question 7

Which ions are produced by acids when they are added to water?

Answer 7

Hydrogen ions, H⁺_(aq).

Question 8

Describe the method of making soluble salts from solutions (neutralisation reaction).

Answer 8

1. Measure out acid and gently warm using bunsen burner for 1 minute max.
2. Add base one spatula at a time until it no longer dissolves (reacts).
3. Filter mixture into evaporating basin to remove unreactive base.
4. Heat basin with bunsen burner or leave to evaporate the water.

Question 9

Describe the method of making soluble salts from solution using an indicator.

Answer 9

1. Measure out acid and add universal indicator.
2. Add base drop by drop until universal indicator turns green (neutral).
3. Add spatula of activated charcoal and stir until solution is clear.
4. Filter solution and evaporate.

Question 10

Describe the method for making insoluble salts from solution (precipitation reaction).

Answer 10

1. Add a soluble salt to another soluble salt.
2. Filter to remove insoluble salt produced.
3. Evaporate to get soluble salt.

Question 11

During electrolysis of sodium chloride solution, one product is hydrogen.

How does a hydrogen ion change into a hydrogen atom?

Answer 11

They gain 1 electron.

Question 12

Suggest why a mixture of sulfuric acid might be heated into a solution.

Answer 12

To increase rate of reaction.

Question 13

Ammonia dissolves in water to produce an alkaline solution. Which ion makes ammonia solution alkaline?

Ammonia= Nitrogen and Hydrogen

Answer 13

Hydroxide.

Question 14

When sodium chloride solution is electrolysed, one product is chlorine.

Name two other products from the electrolysis of sodium chloride solution (2 marks).

Answer 14

Hydrogen (1).

Sodium Hydroxide (1).

Question 15

What is electrolysis?

Answer 15

Electrolysis is the process that uses electricity to break down ionic compounds into elements.

Question 16

Why can ionic compounds only be electrolysed when molten or dissolved in water?

Answer 16

Only when the compounds are molten or dissolved because then their ions are free to move to the electrodes.

Question 17

What are electrodes often made out of?

Answer 17

An inert substance that will not react with the products.

Sometimes, such as in electrolysis of Aluminium Oxide, graphite (carbon) electrodes are used.

Question 18

In electrolysis, where do the positive ions go and where do the negative?

Answer 18

Positive ions go to the negative electrode and gain electrons, so are reduced.

Negative ions go to the positive electrode and lose electrons, so are oxidised.

Question 19

What does ‘OIL RIG’ stand for?

Answer 19

Oxidation Is Lost, Reduction Is Gain.

Question 20

What are halogens?

Answer 20

Group 7 elements, which always pair up.

Question 21

Complete the half equation for the formation of chlorine at the positive electrode: 2Cl^-➝

Answer 21

2Cl^- ➝ Cl₂ + 2e^-.

Question 22

What ions does water contain?

Answer 22

Hydrogen ions and hydroxide ions.

Question 23

When solutions of ions in water are electrolysed, what is produced at the negative electrode?

Answer 23

Hydrogen gas.

Question 24

Why is aluminium oxide mixed with cryolite before being molten and electrolysed?

Answer 24

Cryolite is added to lower the melting point of aluminium oxide so less energy is needed to melt it.

Question 25

Aluminium is 3+ and Oxygen is 2-. What are the half equations for the electrolysis of aluminium oxide?

Answer 25

Cathode: Al³⁺ + 3e^- ➝Al. Anode: 2O₂- ➝O₂ + 4e^-.

Question 26

Carbon electrodes are used in the electrolysis of aluminium oxide. What does this mean?

Answer 26

Oxygen atoms pair to make O₂. O₂ reacts with the carbon electrode to make carbon dioxide. The carbon electrode therefore gets used up so must be replaced.

Question 27

What is the positive electrode called?

Answer 27

Anode.

Question 28

What is the negative electrode called?

Answer 28

Cathode.

Question 29

What is brine?

Answer 29

Brine is a solution of sodium chloride in water.

Question 30

What ions does brine contain?

Answer 30

Sodium ions (Na⁺), Chloride ions (Cl^-), Hydrogen ions (H⁺) and Hydroxide ions (OH^-).

Question 31

What products are produced when brine is electrolysed?

Answer 31

Chlorine gas, hydrogen gas and sodium hydroxide solution.

Question 32

What is sodium hydroxide and what are some of its uses?

Answer 32

Sodium hydroxide is a strong alkali with many uses including making soap, making paper, making bleach, neutralising acids and controlling pH.

Question 33

What is chlorine used for?

Answer 33

Chlorine is used to kill bacteria in drinking water and in swimming pools, and to make bleach, disinfectants and plastics.

Question 34

What is hydrogen used for?

Answer 34

Making margarine and hydrochloric acid.

Question 35

What is electroplating?

Answer 35

Electroplating uses electrolysis to put a thin coating of metal onto an object.

Question 36

Why might electroplating be used?

Answer 36

- To make objects look more attractive. - To protect a metal object from corroding. - To increase the hardness of a surface. - To reduce costs by using a thin layer of metal instead of pure metal.

Question 37

How does electroplating work?

Answer 37

1. The object to be electroplated is made the negative electrode in an electrolysis cell. 2. The plating metal is made the positive electrode. 3. The electrolyte contains ions of the plating metal.

Question 38

The electrolyte contains cryolite. Explain why (2marks).

Answer 38

Cryolite lowers the boiling point of aluminium oxide (1) so less energy/heat is needed to melt it (1).