Chemical Changes

Question 1

List the reactivity series.

Answer 1

Potassium
Sodium
Lithium
Calcium
Magnesium
Aluminium
Carbon
Zinc
Iron
Hydrogen
Copper
Silver
Gold

Question 2

What happens when a metal reacts with water?

Answer 2

Metal + water → metal hydroxide + hydrogen

Question 3

What happens when a metal reacts with a dilute acid?

Answer 3

A salt and hydrogen are formed.

E.g. Magnesium + hydrochloric acid → magnesium chloride + hydrogen

Question 4

How would a metal below hydrogen react with a dilute acid?

Answer 4

It wouldn’t be able to react.

Question 5

What is oxidation and reduction?

Answer 5

Oxidation
Is
Loss
Reduction
Is
Gain
of electrons

Question 6

What is a displacement reaction?

Answer 6

When an more reactive metal displaces a less reactive metal from its compound.

Question 7

What kind of reaction is electrolysis?

Answer 7

Displacement

Question 8

Evaluate the differences between reduction by carbon and electrolysis.

Answer 8

Reduction by carbon can only be done if the metal is less reactive than carbon. Electrolysis is used if the metal is more reactive however it is more expensive as it uses electrical energy.

Question 9

Why is aluminium so expensive?

Answer 9

Electrolysis is used to extract it.

Question 10

What state do the electrolytes in electrolysis need to be in?

Answer 10

Molten or dissolved in water

Question 11

Why does aluminium have to be molten?

Answer 11

It is insoluble

Question 12

Why is aluminium oxide dissolved in cryolite?

Answer 12

The melting point of aluminium oxide is high so a lot of energy must be transferred to break its strong ionic bonds, and this is expensive and cryolite melts at a lower temperature.

Question 13

What happens at the cathode and anode during the electrolysis of aluminium?

Answer 13

• Cathode: aluminium ions are reduced to form aluminium atoms. Al3+ + 3e- → Al
• Anode: oxide ions are oxidised and form oxygen gas. 2O2- → O2 + 4e-

Question 14

What do acids form in aqueous solutions?

Answer 14

Hydrogen ions - H+

Question 15

What do alkalis form in aqueous solutions?

Answer 15

Hydroxide ions - OH-

Question 16

How can the pH of a solution be measured?

Answer 16

• Universal indicator Red — Green — Blue
• Blue litmus paper Red — Blue — Blue

Question 17

What is base?

Answer 17

Any substance that reacts with an acid to form a salt and water.

Question 18

What is a salt?

Answer 18

The substance formed when the hydrogen ion in an acid is replaced by a metal ion.

Question 19

What is an alkali?

Answer 19

A soluble base.

Question 20

What is a neutralisation reaction?

Answer 20

A reaction between an acid and a base.

Question 21

What is the equation for a neutralisation reaction?

Answer 21

H+(aq) + OH-(aq) → H2O(l)

Question 22

What forms when an acid reacts with a metal?

Answer 22

Acid + metal → salt + hydrogen

Question 23

What is the equation for when a metal oxide reacts with acid?

Answer 23

Acid + metal oxide → salt + water

Question 24

What is the reaction when an acid reacts with carbonates?

Answer 24

Acid + carbonate → salt + water + carbon dioxide

Question 25

How is a salt named?

Answer 25

The base, alkali or carbonate is the first section and the second section is the acid. E.g. Hydrochloric acid produces chloride salt

Question 26

How can a soluble salt be formed?

Answer 26

By reacting an acid with an insoluble reactant (e.g. a metal, a metal oxide, a metal hydroxide or a carbonate).

Question 27

How do you make a soluble salt from an acid and an insoluble reactant?

Answer 27

1. Add powdered insoluble reactant to acid in a beaker until it is in excess. 2. Filter the mixture in the beaker to remove the excess solid. The filtrate now contains only the salt and water. 3. Heat the solution in an evaporating dish over a water bath. Until small crystals start to appear - the solution is now saturated. 4. Leave the saturated solution at room temperature for a day or two. This gives time for large crystals to form.

Question 28

When does a solution form?

Answer 28

When a solute dissolves in a solvent.

Question 29

What is the difference between strong acids and weak acids?

Answer 29

String acids completely dissociate into ions whilst weak acids only partially dissociate.

Question 30

What is pH?

Answer 30

A measure of its concentration of hydrogen ions. The higher the concentration of H+ ions in an acidic solution, the lower the pH the lower the concentration of H+ ions in an acidic solution, the higher the pH

Question 31

What are examples of strong and weak acids?

Answer 31

- Nitric acid - Sulphuric acid - Hydrochloric acid - Citric acid

Question 32

What is the electrolyte?

Answer 32

A substance that conducts an electrical current when in the molten state or is dissolved in water.

Question 33

What is electrolysis?

Answer 33

The decomposition of a compound using an electric current.

Question 34

Cations are …

Answer 34

Pawsitive (positive)

Question 35

Anions are …

Answer 35

Nehative

Question 36

What forms at the anode and cathode during the electrolysis of dissolved ionic compounds?

Answer 36

Cathode: the metal is produced if it is less reactive than hydrogen Anode: oxygen is produced unless valued ions are present

Question 37

What is the layout for half equations at the cathode and anode?

Answer 37

Cathode: Na+ + e- → Na Anode: 2Cl- → Cl2 + 2e-