C2 - Salts & Electrolysis

Question 0

What is an alkali?

Answer 0

• A soluble hydroxide.

- Produce OH- ions when added to water.

Question 1

What are acids?

Answer 1

Substances that produce H+ ions when added to water.

Question 2

What are bases?

Answer 2

Substances which neutralise acids.

Question 3

How is acidity measured?

Answer 3

Using a universal indicator with a pH scale.

Question 4

What are soluble hydroxides?

Answer 4

Alkali

Question 5

What are metal oxides and hydroxides?

Answer 5

Bases

Question 6

What pH is pure water?

Answer 6

7 ie. neutral

Question 7

What colour does universal indicator turn for acidic substances?

Answer 7

Red

Question 8

What colour does universal indicator turn for alkali substances?

Answer 8

Purple

Question 9

What is produced when an acid and metal react?

Answer 9

A salt and hydrogen gas

Question 10

What is produced when an acid reacts with a base?

Answer 10

A salt and water

Question 11

What type of reaction occurs between acids and bases?

Answer 11

Neutralisation

Question 12

What is the equation of neutralisation in terms of ions?

Answer 12

H+(aq) + OH-(aq) —-> H2O(l)

Question 13

What is a precipitation reaction?

Answer 13

Combining two solutions that contain different soluble salts which react to make an insoluble salt.

Question 14

How are precipitate reactions used in water treatment?

Answer 14

Raising the pH makes insoluble metal hydroxides precipitate out.

Question 15

What is electrolysis?

Answer 15

Breaking down a substance using electricity.

Question 16

What types of substances can be electrolysed?

Answer 16

Ionic compounds can be electrolysed when they are molten or in solution.

Question 17

What is made from electrolysis?

Answer 17

Positive ions move to the cathode while negative ions move to the anode.

Question 18

What is the electrolyte?

Answer 18

The substance being broken down.

Question 19

What are electrodes made of?

Answer 19

Inert substances such as graphite or platinum.

Question 20

Why are electrodes made of un reactive materials?

Answer 20

So the electrodes don’t react with the electrolyte or the products of electrolysis.

Question 21

What happens to the ions in electrolysis?

Answer 21

Negative ions are oxidised.

Positive ions are reduced.

Question 22

How does water affect the products of electrolysis?

Answer 22

• The less reactive element between hydrogen and the metal is produced at the cathode.
• At the anode, oxygen is often produced from the discharged hydroxide ions.

Question 23

What is reduction?

Answer 23

Gaining electrons

Question 24

What is oxidation?

Answer 24

Losing electrons

Question 25

How is aluminium obtained from aluminium oxide?

Answer 25

Aluminium oxide is electrolysed.

Question 26

Why is cryolite used in aluminium extraction?

Answer 26

Aluminium oxide is mixed with cryolite to lower its melting point.

Question 27

What forms at the cathode during aluminium extraction?

Answer 27

Molten aluminium.

Question 28

What is formed at the anode during aluminium extraction?

Answer 28

Oxygen which reacts with the carbon electrodes making carbon dioxide.

Question 29

Why are the carbon electrodes replaced regularly?

Answer 29

The carbon reacts with oxygen so burns away very quickly.

Question 30

What is produced when brine is electrolysed?

Answer 30

Chlorine gas, hydrogen gas and sodium hydroxide solution.

Question 31

How is chlorine from electrolysis used?

Answer 31

- Make bleach | - Make plastics

Question 32

How is the hydrogen from electrolysis used?

Answer 32

Make margarine

Question 33

How is the sodium hydroxide from electrolysis used?

Answer 33

Make bleach, paper, soap

Question 34

What are the half equations for the electrolysis of brine?

Answer 34

2Cl-(aq) ----> Cl2(g) + 2e- | 2H+(aq) + 2e- ----> H2(g)

Question 35

Give three reasons objects are electroplated.

Answer 35

- Improve their appearance - Protect their surface - Use smaller amounts of precious metals

Question 36

How does electroplating work?

Answer 36

The object is made the cathode. The plating metal is the anode. The electrolyte contains ions of the plating metal.