Unit 4 chemical changes

Question 1

What is the reactivity series?

Answer 1

A list of metals ordered by their reactivity

Question 2

How can the order of reactivity for specific metals be found?

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 added to form a compound?

Answer 3

Oxidation

Question 4

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

Answer 4

Reduction

Question 5

Which metals do not react with acids?

Answer 5

Copper, silver, gold as they are less reactive than hydrogen

Question 6

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

Answer 6

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

Question 7

What is the order of the reactivity series from most reactive to least reactive?

Answer 7

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

Question 8

Explain why silver can be found pure in the Earth’s crust

Answer 8

It is very unreactive

Question 9

What process is used to extract metals less reactive than carbon?

Answer 9

Reduction with carbon

Question 10

Which metals are extracted by reduction with carbon?

Answer 10

Iron, Zinc and Copper

Question 11

What process is used to extract metals more reactive than carbon?

Answer 11

Electrolysis

Question 12

Define an ore

Answer 12

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

Question 13

Define a displacement reaction

Answer 13

A reaction in which a more reactive element takes the place of a less reactive element

Question 14

Define oxidation in terms of electrons

Answer 14

Oxidation is the loss of electrons

Question 15

Define reduction in terms of electrons

Answer 15

Reduction is the gain of electrons

Question 16

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

Answer 16

Aluminium has been reduced and iron has been oxidised

Question 17

Show two half equations for the reaction below:

Al³⁺ + Fe → Fe³⁺ + Al

Answer 17

Al³⁺ + 3e⁻ → Al

Fe → Fe³⁺ + 3e-

Question 18

Define acid in terms of pH

Answer 18

A substance with a pH of less than 7

Question 19

Define acids in terms of ions

Answer 19

A substance which releases H⁺ ions in solution

Question 20

What does (aq) stand for?

Answer 20

Aqueous: when something is dissolved in water

Question 21

State the three common acids and give their formulae

Answer 21

Hydrochloric acid, HCl, Sulphuric acid, H₂SO₄,

Nitric acid, HNO₃

Question 22

What is a neutral solution?

Answer 22

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

Question 23

How do you measure pH?

Answer 23

With an indicator or pH probe

Question 24

What is a base?

Answer 24

A metal oxide, hydroxide or carbonate, they react with acids.

Question 25

What is an alkali?

Answer 25

A soluble base. E.g. sodium hydroxide

Question 26

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

Answer 26

OH⁻

Question 27

What is a salt?

Answer 27

An ionic compound formed during neutralisation

Question 28

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

Answer 28

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

Question 29

What is a neutralisation reaction?

Answer 29

A reaction involving an acid that results in a neutral solution

Question 30

Which ions react together in a neutralization reaction?

Answer 30

H⁺ and OH⁻

Question 31

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

Answer 31

H⁺ + OH⁻ → H2O

Question 32

metal + acid →

Answer 32

→ salt + hydrogen gas

Question 33

MASH

Answer 33

metal + acid → salt + hydrogen gas

Question 34

metal hydroxide + acid →

Answer 34

→ salt + water

Question 35

metal oxide + acid →

Answer 35

→ salt + water

Question 36

BAWS

Answer 36

base + acid → water + salt

Question 37

metal carbonate + acid →

Answer 37

→ salt + water + carbon dioxide

Question 38

CAWCS

Answer 38

metal carbonate → water + carbon dioxide + salt

Question 39

How do you make a pure salt from an acid?

Answer 39

React the acid with an excess base then filter off the excess base. E.g. to make copper sulphate react copper oxide with sulphuric acid

Question 40

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

Answer 40

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

Question 41

What is a strong acid?

Answer 41

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

Question 42

What is a weak acid?

Answer 42

An acid which only partially ionises in water. | E.g. in ethanoic acid, only some of the molecules will have split up into the ethanoate ion and H⁺ ions.

Question 43

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

Answer 43

As an acid increases in strength the pH decreases.

Question 44

What is a concentrated acid?

Answer 44

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

Question 45

What is a dilute acid?

Answer 45

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

Question 46

What is pH a measure of?

Answer 46

pH is measure of concentration of H⁺ in a solution.

Question 47

If the pH increases by 1 what does this mean has happened | to the H+ ion concentration?

Answer 47

It has decreased by a factor of 10

Question 48

How is a titration carried out?

Answer 48

An acid of known concentration is placed in a conical flask with a few drops of indicator. An alkali of unknown concentration is added in until there is a permanent colour change

Question 49

How can you make a titration more accurate?

Answer 49

Do a rough titration first, use a white tile to see the colour change better, add the alkali drop by drop near the end point and repeat it until you get consistent results.

Question 50

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

Answer 50

Oxidation

Question 51

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

Answer 51

Reduction

Question 52

What is electrolysis?

Answer 52

Using electricity to break down a substance

Question 53

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

Answer 53

The ions become free to move around

Question 54

What is an electrolyte?

Answer 54

A solution or liquid containing ions

Question 55

Which electrode do negative ions move to?

Answer 55

Cathode (positive electrode)

Question 56

Which electrode do positive ions move to?

Answer 56

Anode (negative electrode)

Question 57

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

Answer 57

Iron and bromine

Question 58

If electrolysis of a solution containing a metal more reactive than hydrogen is carried out what forms at the cathode?

Answer 58

Hydrogen

Question 59

If electrolysis of a solution containing sulphate, carbonate or nitrate ions what is produced at the anode?

Answer 59

Oxygen

Question 60

What is the main disadvantage of using electrolysis to extract metals?

Answer 60

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

Question 61

Why is aluminium oxide mixed with cryolite when extracting | aluminium?

Answer 61

To lower the melting point

Question 62

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

Answer 62

Aluminium at the cathode and oxygen at the anode

Question 63

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

Answer 63

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

Question 64

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

Answer 64

Chlorine gas and hydrogen gas

Question 65

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

Answer 65

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

Question 66

In the electrolysis of lithium sulphate solution, what are the products?

Answer 66

Hydrogen gas and oxygen gas