Chemical reactions

Question 1

What is the reactivity series?

Answer 1

A list of elements ordered by their reactivity

Question 2

How can metals be placed in order of their reactivity?

Answer 2

Add the metals to water or acid and see which ones react the most (by how much fizzing there is)

Question 3

What is the name for a reaction where oxygen is removed from a compound?

Answer 3

Reduction

Question 4

Explain why zinc can be extracted from zinc oxide with carbon but magnesium cannot be extracted from magnesium oxide with carbon

Answer 4

Magnesium is more reactive than carbon (1), Zinc is less reactive than carbon (1), Carbon can therefore remove oxygen from zinc oxide but not magnesium oxide (1)

Question 5

Explain why gold and silver can be found naturally in the Earth’s crust

Answer 5

It is very unreactive

Question 6

What process is used to extract metals more reactive than carbon

Answer 6

Electrolysis

Question 7

Define an ore

Answer 7

A material containing enough metal in it for it to be economically worthwhile to extract the metal.

Question 8

Define a displacement reaction

Answer 8

A reaction in which a more reactive element takes the place of a less reactive element in one of its compounds or in solution

Question 9

Define oxidation in the context of loss and gain of electrons

Answer 9

Oxidation is the loss of electrons

Question 10

Define reduction in the context of loss and gain of electrons

Answer 10

Reduction is the gain of electrons

Question 11

Which of the substances below has been oxidized and which has been reduced? Al³⁺ + Fe → Fe³⁺ + Al

Answer 11

Aluminium has been reduced and iron has been oxidised

Question 12

Show two half equations for the reaction below: Al³⁺ + Fe → Fe³⁺ + Al

Answer 12

Al³⁺ + 3e⁻ → Al, Fe → Fe³⁺ + 3e-

Question 13

Define acid in terms of pH

Answer 13

A substance with a pH of less than 7

Question 14

Define acids in terms of ions

Answer 14

A substance which releases H⁺ ions in solution

Question 15

What does (aq) stand for?

Answer 15

Aqueous: when something is dissolved in water. E.g. NaCl(aq) is salt water

Question 16

State the three common acids and give their formulae

Answer 16

Hydrochloric acid, HCl(aq), Sulphuric acid, H₂SO₄(aq), Nitric acid, HNO₃

Question 17

Which ions do the common acids form in solution?

Answer 17

HCl forms H⁺ and Cl⁻, H₂SO₄ forms 2H⁺ and SO₄²⁻, HNO₃ forms H⁺ and NO₃⁻

Question 18

What is a neutral solution?

Answer 18

A solution with a pH of 7. Water is an example.

Question 19

How do you measure pH?

Answer 19

With an indicator or pH probe.

Question 20

What is a base?

Answer 20

A metal oxide, hydroxide or carbonate that will react with an acid. E.g. copper oxide

Question 21

What is an alkali?

Answer 21

A soluble base. E.g. sodium hydroxide

Question 22

Which ions are always present in a solution of an alkali?

Answer 22

OH⁻

Question 23

What is a salt?

Answer 23

A compound formed when some or all of the hydrogen from an acid is replaced by a metal. E.g. CuSO₄, copper sulphate, where copper has replaced H from H₂SO₄

Question 24

What type of salts are formed by the three main acids?

Answer 24

Hydrochloric acid produces chlorides, sulphuric acid = sulphates, nitric acid = nitrates

Question 25

What is a neutralisation reaction?

Answer 25

A reaction involving an acid that results in a neutral solution

Question 26

Which ions always react together in a neutralization reactions between acids and alkalis?

Answer 26

H⁺ and OH⁻

Question 27

Write the equation showing the reaction between H⁺ and OH⁻ ions

Answer 27

H⁺ + OH⁻ → H₂O

Question 28

metal + acid →

Answer 28

→ salt + hydrogen gas

Question 29

metal hydroxide + acid →

Answer 29

→ salt + water

Question 30

metal oxide + acid →

Answer 30

→ salt + water

Question 31

metal carbonate + acid →

Answer 31

→ salt + water + carbon dioxide

Question 32

How do you make a soluble salt from an acid?

Answer 32

React the acid with a base. E.g. to make copper sulphate react copper oxide with sulphuric acid

Question 33

If a salt is in solution, how do you extract it as a solid?

Answer 33

Allow the water to evaporate off and it will leave the salt behind as a solid.

Question 34

What is a strong acid?

Answer 34

An acid which completely splits up into its ions in water. E.g. when HCl is in water all the HCl molecules split up into H⁺ and Cl⁻

Question 35

What is a weak acid?

Answer 35

An acid which will have some molecules which do not split up into their ions. E.g. in ethanoic acid only some of the molecules will have split up into the ethanoate ion and H⁺ ions.

Question 36

What is the relationship between the strength of an acid and its pH?

Answer 36

As an acid increases in strength the pH decreases.

Question 37

What is a concentrated acid?

Answer 37

An acid where there are lots of acid particles in the water.

Question 38

What is a dilute acid?

Answer 38

An acid where there are fewer acid particles in the water.

Question 39

How is pH measured?

Answer 39

pH is related to the concentration of H⁺ in a solution.

Question 40

Which ions are in NaCl

Answer 40

Na⁺ and Cl⁻

Question 41

Which ions are in CaCO₃

Answer 41

Ca²⁺ and CO₃²⁻

Question 42

Which ions are in Mg(OH)₂

Answer 42

Mg²⁺ and 2 ions of OH⁻

Question 43

Which ions are in H₂SO₄

Answer 43

2 ions of H⁺ and one SO₄²⁻

Question 44

Which ions are in NH₄OH

Answer 44

NH₄⁺ and OH⁻

Question 45

Which ions are in (NH₄)₂O

Answer 45

2 ions of NH₄⁺ and one O²⁻

Question 46

What is the formula of calcium chloride?

Answer 46

CaCl₂

Question 47

What is the formula of aluminium nitrate?

Answer 47

Al(NO₃)₃

Question 48

What is the formula of iron (III) oxide?

Answer 48

Fe₂O₃

Question 49

What is the formula of magnesium fluoride?

Answer 49

MgF₂

Question 50

What is the formula of sodium sulphate?

Answer 50

Na₂SO₄

Question 51

What is the formula of copper (I) oxide

Answer 51

Cu₂O

Question 52

Is this process oxidation or reduction? Al → Al³⁺ + 3e⁻

Answer 52

Oxidation

Question 53

Is this process oxidation or reduction? Na⁺ + e⁻ → Na

Answer 53

Reduction

Question 54

Is this process oxidation or reduction? F₂ + 2e⁻ → 2F⁻

Answer 54

Reduction

Question 55

Is this process oxidation or reduction? Fe²⁺ → Fe³⁺ + e⁻

Answer 55

Oxidation

Question 56

Balance this ionic equation: Ca + Na⁺ → Ca²⁺ + Na

Answer 56

Ca + 2Na⁺ → Ca²⁺ + 2Na

Question 57

Balance this ionic equation: Mg²⁺ + Na → Na⁺ + Mg

Answer 57

Mg²⁺ + 2Na → 2Na⁺ + Mg

Question 58

Balance this ionic equation: Al + Ca²⁺ → Al³⁺ + Ca

Answer 58

2Al + 3Ca²⁺ →2Al³⁺ + 3Ca

Question 59

In this reaction, what has been oxidised and what has been reduced? Mg²⁺ + 2Na → 2Na⁺ + Mg

Answer 59

Na has been oxidised, Mg²⁺ has been reduced

Question 60

In this reaction, what has been oxidised and what has been reduced? 2Al + 3Ca²⁺ → 2Al³⁺ + 3Ca

Answer 60

Al has been oxidised, Ca²⁺ has been reduced

Question 61

In this reaction, what has been oxidised and what has been reduced? K + Na⁺ → K⁺ + Na

Answer 61

K has been oxidized, Na⁺ has been reduced

Question 62

What is electrolysis?

Answer 62

Using electricity to break down a substance

Question 63

What happens to an ionic substance when it is melted or dissolved in water?

Answer 63

The ions become free to move around

Question 64

What is the name for the positive electrode?

Answer 64

The anode

Question 65

What is the name for the negative anode?

Answer 65

The cathode

Question 66

Do positive ions move to the anode or the cathode?

Answer 66

Cathode

Question 67

Do negative ions move to the anode or the cathode?

Answer 67

Anode

Question 68

At which electrode would Zn²+(aq) turn into Zn(s)?

Answer 68

Cathode (needs to gain electrons)

Question 69

At which electrode would Cl⁻(aq) turn into Cl₂(g)?

Answer 69

Anode (needs to lose electrons)

Question 70

Balance the equation: Al³⁺ + e⁻ → Al

Answer 70

Al³⁺ + 3e⁻ → Al

Question 71

Balance the equation: Cl⁻ → Cl₂ + e⁻

Answer 71

2Cl⁻ → Cl₂ + 2e⁻

Question 72

Balance the equation: O²⁻ → O₂ + e⁻

Answer 72

2O²⁻ → O₂ + 4e⁻

Question 73

What will be the products for the electrolysis of molten iron bromide?

Answer 73

Iron and bromine

Question 74

What will be the products for the electrolysis of molten zinc oxide?

Answer 74

Zinc and oxygen

Question 75

For the extraction of which metals is electrolysis needed?

Answer 75

Ones more reactive than carbon, e.g. aluminium

Question 76

What are the two main disadvantages of using electrolysis to extract metals?

Answer 76

Requires a large amount of energy to melt the compounds and to produce the necessary electricity

Question 77

Why is aluminium oxide mixed with cryolite when extracting aluminium?

Answer 77

To lower the melting point

Question 78

What is produced at the anode and cathode in the electrolysis of aluminium oxide?

Answer 78

Aluminium at the cathode and oxygen at the anode

Question 79

Why does the anode need to be replaced in the electrolysis of aluminium oxide?

Answer 79

The oxygen reacts with the carbon electrode to produce carbon dioxide.

Question 80

In the electrolysis of sodium chloride solution, what are the products?

Answer 80

Chlorine gas and hydrogen gas

Question 81

Why is sodium not produced in the electrolysis of sodium chloride solution?

Answer 81

It is more reactive than hydrogen so hydrogen is produced instead.

Question 82

What is produced at the anode in electrolysis of solutions?

Answer 82

Either a halogen or oxygen (when there is no halogen present)

Question 83

What is a chemical cell?

Answer 83

A unit which contains chemicals which produce electricity through a reaction

Question 84

What are the main components of a chemical cell?

Answer 84

An anode, a cathode and an electrolyte

Question 85

What is an electrolyte?

Answer 85

A solution containing ions which allows current to flow.

Question 86

What does the potential difference of a cell depend on?

Answer 86

The type of electrode and the electrolyte.

Question 87

What is a battery?

Answer 87

Two or more cells connected in series

Question 88

What happens to the electrodes in a chemical cell?

Answer 88

The more reactive metal depletes and the less reactive one increases in size.

Question 89

In non-rechargeable cells, why do the chemical reactions stop over time?

Answer 89

One of the reactants becomes used up.

Question 90

How can certain cells be recharged?

Answer 90

Applying an external electric current

Question 91

How does the reactivity of the metal electrodes affect the size of the potential difference?

Answer 91

The greater the difference in reactivity, the greater the potential difference.

Question 92

What is a fuel cell?

Answer 92

A cell which uses a fuel and oxygen (or air) to generate electricity.

Question 93

What are the products in a hydrogen fuel cell?

Answer 93

Water

Question 94

State three advantages of hydrogen fuel cells

Answer 94

Do not need to be recharged, no pollutants are produced, can be different sizes for different uses

Question 95

State three disadvantages of hydrogen fuel cells

Answer 95

Hydrogen is highly flammable, hydrogen is sometimes produced through non-renewable means, hydrogen is difficult to store

Question 96

Complete the equation which occurs at the negative electrode of a hydrogen fuel cell 2H₂ + 4OH⁻ →

Answer 96

4H₂O + 4e⁻

Question 97

Complete the equation which occurs at the positive electrode of a hydrogen fuel cell O₂ + 2H₂O →

Answer 97

4OH⁻