C2.5 Salts and electrolysis

Question 1

What is a base?

Answer 1

substances that neutralise acids

Question 2

What is an alkali?

Answer 2

a soluble hydroxide , produces OH- ions when added to water

Question 3

What does the pH scale show?

Answer 3

how acidic or alkaline a substance is

Question 4

What ions make something acidic?

Answer 4

H+ ions

Question 5

What is produced when an acid and metal react?

Answer 5

Acid + Metal = salt + hydrogen

Question 6

What is produced when and acid and base react?

Answer 6

Acid = Base = salt + water

Question 7

What is the reaction between an acid and base called?

Answer 7

a neutralisation reaction

Question 8

What is electrolysis?

Answer 8

the separation of substances using electricity

Question 9

What does adding ammonium solution to an acid produce?

Answer 9

an ammonium salt (eg. ammonium nitrate) and water

Question 10

What is the positive electrode called?

Answer 10

anode

Question 11

What is the negative electrode called?

Answer 11

cathode

Question 12

How can an insoluble salt be made?

Answer 12

reacting two solutions to produce a precipitate

Question 13

What can be electrolysed?

Answer 13

Ionic compounds when they are molten or in a solution this is because their ions are then free to move to the electrodes

Question 14

Which ions move where during electrolysis?

Answer 14

negative ions (an ions) move to the positive electrode (anode)
positive ions(cat ions) move to the negative electrode (cathode)

Question 15

What happens at the electrodes?

Answer 15

negative(cathode)-reduction, positive ions are reduced

positive(anode)-oxidation, negative ions are oxidised

Question 16

What effect does water have on electrolysis?

Answer 16

The less reactive element between hydrogen and the metal is usually produced at the negative electrode.
At the positive electrode, hydroxide usually discharges, giving off oxygen gas (except when there is large concentration of halide ions in solution(group 7) in this case the halide is discharged)

Question 17

How is electrolysis used to extract aluminium?

Answer 17

aluminium oxide is electrolysed when manufacturing aluminium metal
it is mixed with molten cryolite to lower its melting point
aluminium forms at the negative electrode and oxygen at the positive electrode

Question 18

What are the electrodes replaced often during the electrolysis of aluminium?

Answer 18

because they are made of carbon and this is gradually burnt/worn away by the oxygen forming carbon dioxide

Question 19

What are the product when we electrolyse brine?

Answer 19

hydrogen, chlorine and sodium hydroxide solution

Question 20

What is formed at the negative electrode when electrolysing brine?

Answer 20

Hydrogen ions (H+) formed when water breaks down are attracted as well as sodium ions (Na+) but as hydrogen is less reactive it is formed here as a gas (H2)

Question 21

What is formed at the positive electrode when electrolysing brine?

Answer 21

Chloride ions (Cl-) are attracted to the positive electrode
they are lose one electron and the ions are oxidised
they bond together in pairs and are given off as chlorine gas (Cl 2)

Question 22

What are the uses of hydrogen?

Answer 22

useful in food industry (very pure hydrogen)

make margarine by reacting with vegetable oils

Question 23

What are the uses of chlorine?

Answer 23

can react with sodium hydroxide to make bleach (good at killing bacteria)
makes disinfectants, and plastics eg. PVC

Question 24

What are the uses of sodium hydroxide?

Answer 24

used to make soap and paper

also used with chlorine to make bleach

Question 25

What is electroplating?

Answer 25

covering an object with a thin layer of metal by electrolysis

Question 26

How does electroplating work?

Answer 26

the object to be electroplated is made the negative electrode in electrolysis cell
the plating metal is made the positive electrode
the electrolyte contains ions of the plating metal

Question 27

Why do we electroplate objects?

Answer 27

to improve their appearance
protect their surfaces
use smaller amounts of precious metals