Topic 4 - Chemical Changes

Question 1

Define Oxidation.

Answer 1

Oxidation is gain of oxygen.

Question 2

Define reduction.

Answer 2

Loss of oxygen.

Question 3

What is formed when metals react with oxygen?

Answer 3

Metal oxide.

Question 4

What is the general formula when metals react with water?

Answer 4

Metal + water –> metal hydroxide + hydrogen

Question 5

What are observation when metals react with water?

Answer 5

Metal dissolves and fizzing is present as hydrogen gas released.
If universal indicator is added it will turn purple as hydroxide is alkali.
More reactive metals react more quickly and vigorously.

Question 6

What is the general formula when metals react with acid?

Answer 6

Metal + acid –> Salt + Hydrogen

Question 7

What metals do not react with dilute acids?

Answer 7

A metal below hydrogen on the reactivity series will not react with hydrogen. This is because since they are less reactive than hydrogen they are unable to displace it.

Question 8

What is reactivity in metals?

Answer 8

How easily it can form positive metal ions,

Question 9

Define a displacement reaction.

Answer 9

Where a more reactive element can displace a less reactive element in a compound.

Question 10

How is gold found in the earth?

Answer 10

Since it is unreactive it is found in the earth as pure metals.

Question 11

How can metals be extracted when are less reactive than carbon from their oxides?

Answer 11

They can be extracted by reducing them with carbon.

Question 12

What is OILRIG

Answer 12

Oxidation is loss of electrons.
Reduction is gain of electrons.

Question 13

Write the ionic equation for this.

Answer 13

1) All aqueous substances can be broken down into their ions!!
2) Then when an ion is on both sides of an equation it is called a spectator ion. We can cancel spectator ions as they do not do anything.
3) This leaves us with the ionic equation.

Question 14

Write the half equations for this.

Answer 14

1) When there is an ionic equation you can split it into 2 half equations.

Question 15

What ions are produced when you put hydrochloric acid into water?

Answer 15

Dissociates to form H+ and Cl- ions.

Question 16

What ions are produced when you put Sulfuric acid into water.

Answer 16

Question 17

What is the formula for nitric acid and what ions are produced when you put it in water?

Answer 17

Question 18

What type of reaction is a metal with a acid?

Answer 18

It is a redox reaction. - Where both oxidation and reduction occur at the same time.

Question 19

What are the two neutralisation reactions called.

Answer 19

Acid + Metal Carbonate –> Salt + water + carbon dioxide.
Acid + Metal hydroxide –> salt + water

Question 20

How do produce soluble salt from an insoluble base.

Answer 20

Question 21

What ions do acids produce in aqueous solutions?

Answer 21

Hydrogen ions H+

Question 22

What ions do alkalis produce in aqueous solutions?

Answer 22

Hydroxide ions OH-

Question 23

What is the ionic equation for neutralisation?

Answer 23

Question 24

Why do we use titration?

Answer 24

To work out the concentration of an unknown solution in a reaction between an acid and an alakil.

Question 25

Answer 25

0.2

Question 26

Define a strong acid.

Answer 26

An acid that is completely ionised in aqueous solutions.

Question 27

Define a weak acid.

Answer 27

An acid that is only partially ionised in aqueous solutions.

Question 28

What is the difference between a concentrated acid and a dilute acid?

Answer 28

Concentrated acid has a lot of acid per unit volume whereas a dilute acid has a small amount of acid per unit volume.

Question 29

Define electrolysis.

Answer 29

Electrolysis is the process of splitting up a ionic compound using electricity.

Question 30

Define an electrolyte.

Answer 30

A liquid or solution that is able to conduct electricity.

Question 31

What are the positive ions and negative ions in the solution attracted to?

Answer 31

Positive ions = the negative electrode the cathode. Negative ions = The positive electrode the anode. This completes the circuit.

Question 32

In electrolysis in molten ionic compounds which ions gain and which ion loses electrons?

Answer 32

Positive ion gains electrons from the cathode. Negative ions lose electrons at the anode.

Question 33

When do we use electrolysis to extract a metal?

Answer 33

If the metal is more reactive than carbon or if it will react with carbon.

Question 34

How is aluminium extracted?

Answer 34

It is extracted from aluminium oxide by electrolysis. 1) Aluminium oxide is mixed with cryolite. 2) The mixture is heated until it melts. 3) This mixture is electrolysed using graphite electrodes. 4) Aluminium forms at the cathode. 5) Oxygen forms at the anode.

Question 35

What happens in terms of electrons when extracting aluminium?

Answer 35

At the cathode, aluminium ions gain electrons, forming aluminum atoms. So aluminium ions are reduced. At the anode oxygen lose electrons, forming oxygen gas. This is called oxidation.

Question 36

In electrolysis of molten ionic compound what is formed at each electrode?

Answer 36

At the anode (positive electrode) - Non-metal is formed and they are oxidised so they lose electrons. At the cathode (Negative electrode) - Metal is formed and they are reduced so they gain electrons.

Question 37

Why is cryolite used?

Answer 37

Cryolite decreases melting temperature decreasing the cost as less energy is needed.

Question 38

Why must the anode be replaced continually when extracting aluminum?

Answer 38

Oxygen is formed at anode which reacts with reacts with the carbon graphite anode to make carbon dioxide.

Question 39

Why is electrolysis of aqueous solutions more beneficial?

Answer 39

As less energy is required.

Question 40

What is produced at the cathode in electrolysis of aqueous solutions?

Answer 40

Hydrogen is produced if the metal is more reactive than hydrogen. If the metal is not more reactive than the metal is produced.

Question 41

What is produced at the anode in electrolysis of aqueous solutions?

Answer 41

If halide ions are present (group 7) - Then halogen produced. If no halide ions are present then oxygen is produced.