Combined Chemistry - C4 Chemical Changes

Question 1

What two non-metals are often included in the reactivity series?

Answer 1

Hydrogen and Carbon

Question 2

What is the name for the reaction that involves the gaining of oxygen?

Answer 2

Oxidation

Question 3

If an atom is very reactive, is it more or less likely to turn into an ion?

Answer 3

More likely

Question 4

What type of reaction is shown by the equation below?

magnesium + oxygen → magnesium oxide

Answer 4

Oxidation

Question 5

What is that name for the reaction that involves the removal of oxygen?

Answer 5

Reduction

Question 6

Put the following elements in order of reactivity from least to most reactive:

iron / lithium / zinc / copper / potassium / calcium / sodium / magnesium

Answer 6

(least reactive) copper – iron – zinc – magnesium – calcium – lithium – sodium – potassium (most reactive)

Question 7

Why can’t aluminium be extracted by reduction with carbon?

Answer 7

Aluminium is more reactive than carbon

Question 8

What chemical reaction is shown by the equation below to extract iron from iron oxide?

Iron oxide + carbon → iron + carbon dioxide

Answer 8

Reduction (with carbon)

Question 9

Q. Complete the general equation:

Metal + Acid →

Q. Complete the general equation:

Metal + Water →

Answer 9

• Metal + Acid → Salt + Hydrogen
• Metal + Water → Metal hydroxide + Hydrogen

Question 10

Q. Complete the general equation:

Acid + Metal Carbonate →

Q. Complete the general equation:

Acid + Metal oxide →

Answer 10

Acid + Metal carbonate → Salt + Water + Carbon dioxide

Acid + Metal oxide → Salt + Water

Question 11

What type of separation process would you use to separate a soluble salt?

Answer 11

Crystallisation

Question 12

What type of separation process would you use to separate an insoluble salt?

Answer 12

Filtration

Question 13

Why is gold found naturally in the Earth, but other metals are locked up in compounds?

Answer 13

Gold is unreactive

Question 14

Name the ‘salt’ produced when the following chemicals react:

a) Sodium carbonate + nitric acid
b) Magnesium oxide + sulfuric acid
c) Iron hydroxide + hydrochloric acid

*these are just examples, you need to be able to do this for any base reacting with hydrochloric, sulfuric and nitric acid.

Answer 14

a) Sodium nitrate
b) Magnesium sulfate
c) Iron chloride

Question 15

Write the formulae of the following salts using the formulae of ions provided below.

Formulae of common ions: Na⁺, Cl^-, Mg²⁺

a) Sodium Chloride
b) Magnesium Chloride

*these are just examples, you need to be able to do this for any salt when given the formulae of common ions

Answer 15

a) NaCl
b) MgCl₂

Question 16

Describe how you would make a pure, dry sample of a soluble salt using an insoluble base and an acid.

Answer 16

• Add base in excess to acid.
• Filter excess base.
• Crystallisation – to separate salt from its solution.

Question 17

a) What is the pH range of acids?
b) What is the pH range of alkalis?
c) What is the pH of a neutral solution?

Answer 17

a) 0-6
b) 8-14
c) 7

Question 18

Name the ion found in alkaline solutions

Answer 18

Hydroxide ion, OH^-

Question 19

Write an ionic equation for neutralisation

Answer 19

H⁺ (aq) + OH^- (aq) → H₂O (l)

Question 20

What is the name for the separation process shown in the diagram?

Answer 20

Electrolysis

Question 21

Name the ion found in acidic solutions

Answer 21

Hydrogen ion, H⁺

Question 22

What is the name for the reaction when an acid reacts with an alkali to make a salt + water?

Answer 22

Neutralisation reaction

Question 23

When there are several ions in solution, which ion will collect:

a) At the anode?
b) At the cathode?

Answer 23

a) At the cathode: Hydrogen is produced if the metal is more reactive than Hydrogen
b) At the anode: Oxygen is produced unless the solution contains halide ions, then the halogen is produced.

Question 24

What is the name for the liquid that contains the ions in the electrolysis process?

Answer 24

Electrolyte

Question 25

In electrolysis, what is the positive electrode called?

Answer 25

Anode

Question 26

To which electrode are positive ions attracted to?

Answer 26

Negative electrode (opposites attract)

Question 27

In the electrolysis of lead bromide, what collects at:

a) The positive electrode (the anode)?
b) The negative electrode (the cathode)?

Answer 27

• Bromine (at the anode)
• Lead (at the cathode)

Question 28

Why must aluminium be extracted by electrolysis?

Answer 28

It is more reactive than carbon (and therefore can’t be extracted by reduction with carbon)

Question 29

In electrolysis, what is the negative electrode called?

Answer 29

Cathode

Question 30

To which electrode are negative ions attracted to?

Answer 30

Positive electrode (opposites attract)

Question 31

Why does a metal compound have to be molten or dissolved for electrolysis to work?

Answer 31

Because the ions need to be free to flow

Question 32

Why is cryolite used in the electrolysis of aluminium oxide?

Answer 32

To lower the melting point of aluminium oxide (to save energy and costs)

Question 33

Why does the positive electrode have to be regularly replaced in the extraction of aluminium oxide?

Answer 33

• Because oxide ions react with the carbon electrode…
• …Releasing CO₂…
• …Meaning the electrodes gradually degrade

Question 34

Higher Q. Fill in the blanks:

Oxidation is the _____ of electrons.

Reduction is the _____ of electrons.

Answer 34

• Oxidation is the loss of electrons
• Reduction is the gain of electrons

Question 35

Higher Q. In the following equation, state which species are oxidised and which are reduced?

2Fe₂O₃ + 3C → 4Fe + 3CO₂

*this is just an example, you need to be able to do this for any given reaction.

Answer 35

• 2Fe₂O₃ (Iron oxide) is reduced
• 3C (carbon) is oxidised

Question 36

Higher Q. Explain why the reaction below is a redox reaction.

Zn (s) + 2HCl (aq) → ZnCl₂ (aq) + H₂ (g)

Answer 36

• Zinc atoms are oxidised.
• Hydrogen atoms are reduced.
• Hence reduction and oxidation happen at the same time so it’s called a redox reaction.

Question 37

Higher Q. Write an ionic equation for each of the displacement reactions below:

a) Mg + CuSO₄ → Cu + MgSO₄
b) Fe + CuCl₂ → Cu + FeCl₂

*these are just examples, you need to be able to do this for any displacement reaction.

Answer 37

a) Mg(s) + Cu²⁺(aq)→ Cu(s) + Mg²⁺(aq)
b) Fe(s) + Cu²⁺(aq) → Cu(s) + Fe²⁺ (aq)

Question 38

Higher Q. In the following equation, state which species are oxidised and which are reduced?

a) Mg (s) + 2HCl (aq) → MgCl₂ (aq) + H₂ (g)

*this is just an example, you need to be able to do this for reactions between the following metals (magnesium, zinc, iron) and the following acids (hydrochloric and sulfuric)

Answer 38

• Magnesium atoms (Mg) are oxidised.
• Hydrogen ions (H⁺) are reduced.

Question 39

Higher Q. During electrolysis, what happens to ions at the:

a) Cathode?
b) Anode?

Answer 39

• At the Cathode: Ions gain electrons and turn into atoms (Reduction)
• At the Anode: Ions lose electrons and turn into atoms (Oxidation)

Question 40

Higher Q. Write half equations at the anode and cathode for the electrolysis of water.

Answer 40

Anode: 4OH^- - 4e^- → O₂ + 2H₂O

or 4OH^- → O₂ + 2H₂O + 4e^-

Cathode: 2H⁺ + 2e^- → H₂

Question 41

Higher Q. Give two examples of strong acids and two examples of weak acids.

Answer 41

• Strong acids include: Hydrochloric, Nitric and Sulfuric
• Weak acids include: Carbonic, Ethanoic and Citric

Question 42

Higher Q. What is a ‘weak’ acid?

Answer 42

An acid that is only partially ionised in water

Question 43

Higher Q. If you compared the pH of a 1M Strong Acid and a 1M Weak acid, which would have the higher pH and why?

Answer 43

The weaker acid will have the higher pH because it only partially ionises in water (or vice versa).

Question 44

Higher Q. As the hydrogen ion concentration of a solution increases by a factor of 10, what happens to the pH of the solution?

Answer 44

The pH decreases by 1 unit

Question 45

Higher Q. Write the half equations at the anode and cathode for the electrolysis of lead bromide.

*this is just an example, you need to be able to do this for any given electrolysis example.

Answer 45

Anode: 2Br^- - 2e^- → Br₂ or 2Br^- → Br₂ + 2e^-

Cathode: Pb²⁺ + 2e^- → Pb