C4 - Chemical Changes

Question 1

pH scale

Answer 1

A measure of how acidic or alkaline a solution is

Question 2

lower pH means

Answer 2

The more acidic it is

Question 3

higher pH means

Answer 3

More alkaline it is

Question 4

pH7 is a …

Answer 4

neutral substance

Question 5

pH indicator

Answer 5

A dye that changes colour depending on whether it’s above or below a certain pH. Some indicators contain a mixture of dyes that means they gradually change colour over a broad range of pH. These are called wide range indicators and they’re ysefyl for estimating the pH of a solution.

Question 6

Universal Indicator

Answer 6

Standard ph indicator

Question 7

pH meter

Answer 7

Consists of a pH probe used to measure pH electronically. It displays a numerical value which is more accurate than an indicator

Question 8

What do acids form?

Answer 8

Aqueous solutions with a pH of less than 7.

Question 9

What do acids form in water?

Answer 9

H+ ions

Question 10

Base

Answer 10

A substance with a pH greater than 7

Question 11

Alkali

Answer 11

• Base that dissolves in water to form a solution

- pH greater than 7

Question 12

What do Alkalis form in water?

Answer 12

OH- ions

Question 13

Neutralisation

Answer 13

The reaction between acids and bases

Question 14

Neutralisation word equation

Answer 14

acid + base -> salt + water

Question 15

Neutralisation equation with terns if H+ and OH- ions

Answer 15

H+(aq) + OH-(aq) -> H2O(l)

Question 16

What happens to the products of neutralisation?

Answer 16

• Products are neutral (have a pH of 7)

- An indicator can be used to show that a neutralisation reaction is over

Question 17

What do acids produce in water?

Answer 17

They produce hydrogen ions, H+

Question 18

Strong acids

Answer 18

Ionise completely in water. All acid particles dissociate to release H+ ions

Question 19

Weak acids

Answer 19

Don’t fully ionise in solution. Only a small proportion of acid particles dissociate to release H+ ions

Question 20

Ionisation of a weak acid

Answer 20

• Reversible reaction
• Sets up an equilibrium between the undissociated and dissociated acid
• Since only a few of the acid particles release H+ ions, the position of equilibrium lies well to the left

Question 21

How does the concentration of H+ ions in the solution change the reaction?

Answer 21

If the concentration of H+ ions is higher, the rate of concentration will be faster, so strong acids will be more reactive than weak acids of the same concentration.

Question 22

What does pH determine in an acid or alkali?

Answer 22

The measure of concentration of H+ ions in the solution

Question 23

For every decrease of 1 on the pH scale, what happens to the concentration of H+ ions?

Answer 23

Increases by a factor of 10

Question 24

pH of strong acid vs weak acid in the same concentration

Answer 24

pH of a strong acid is always less than pH of a weak acid

Question 25

Acid strength

Answer 25

Proportion of the acid molecules ionise in water

Question 26

What does concentration measure in acids

Answer 26

How much acid there is in a certain volume of water

Question 27

Relation between pH and concentration

Answer 27

pH decreases when acid concentration increases

Question 28

Are metal oxides and metal hydroxides alkalis?

Answer 28

Yes

Question 29

What happens when bases don't dissolve in water?

Answer 29

It doesn't matter because neutralisation still takes place

Question 30

How do metal carbonates change the the products of neutralisation?

Answer 30

Products are now salt, water and carbon dioxide

Question 31

Reactivity series

Answer 31

- Potassium - Sodium - Lithium - Calcium - Magnesium - Carbon - Zinc - Iron - Hydrogen - Copper

Question 32

How are metals listed in the Reactivity Series?

Answer 32

- How reactive they are towards other substances - The higher up it is, the more easily the form positive ions - A higher metal reacts easily with water or an acid

Question 33

How can a reaction between metals and acids reflect their reactivity?

Answer 33

- The faster the reaction is (when there are more hydrogen bubbles being given off), the more reactive the metal is

Question 34

Oxidation

Answer 34

The reaction with oxygen to form oxides

Question 35

Reduction reaction

Answer 35

A reaction that separates a metal from its oxide

Question 36

Oxidation is gain of ...

Answer 36

Oxygen to make an oxide

Question 37

Reduction is loss of ...

Answer 37

Oxygen to make the pure metal

Question 38

What are some other ways to extract metals?

Answer 38

- With carbon using reduction - The ore is reduced as oxygen is removed, and the carbon is oxidised with oxygen - The position of the metal in the reactivity series determines whether it can be extracted with carbon

Question 39

If the position of a metal is higher than carbon, we can extract the metal using ...

Answer 39

Electrolysis

Question 40

If the position of a metal is lower than carbon, we can extract the metal using ...

Answer 40

Reduction using carbon

Question 41

Why can some metals be mined in it's elemental form?

Answer 41

They are so unreactive

Question 42

Oxidation (electrons)

Answer 42

The loss of electrons

Question 43

Reduction (electrons)

Answer 43

A gain of electrons

Question 44

OIL RIG (electrons)

Answer 44

Oxidation Is Loss, Reduction Is Gain

Question 45

REDOX

Answer 45

REDuction and OXidation happen at the same time

Question 46

Displacement reactions

Answer 46

A metal kicking another one out of a compound

Question 47

Rule for displacement reactions

Answer 47

A more reactive metal will displace a less reactive metal from its compound

Question 48

What is reduced in displacement reactions?

Answer 48

The metal ion

Question 49

What is oxidised in displacement reactions?

Answer 49

The metal atom

Question 50

Ionic equation

Answer 50

The particles that react and the products they form are shown (focuses on the substances which are oxidised or reduced)

Question 51

Spectator ions

Answer 51

Ions that don't change in the reaction, which you can just not write in the equation

Question 52

Electrolysis

Answer 52

The chemical decomposition produced by passing an electric current through a liquid or solution containing ions.

Question 53

Where do the positive ions in the electrolyte move to?

Answer 53

- Cathode (-ve electrode) | - Reduction (gain electrons)

Question 54

Where do the negative ions in the electrolyte move?

Answer 54

- Move towards the anode (+ve electrode) | - Oxidised (lose electrons)

Question 55

Why is a flow of charge created through the electrolyte?

Answer 55

Ions travel to the electrodes

Question 56

What happens when ions gain or lose electrons during electrolysis?

Answer 56

They form the uncharged element and are discharged from the electrolyte

Question 57

Electrolyte

Answer 57

The liquid or solution that can conduct electricity

Question 58

Electrode

Answer 58

A solid that conducts electricity and is submerged in the electrolyte

Question 59

Why can't an ionic solid be electrolysed?

Answer 59

The ions are in a fixed position and can't move

Question 60

Why can molten ionic compounds be electrolysed?

Answer 60

The ions can move freely and conduct electricity

Question 61

What happens to molten liquids in electrolysis?

Answer 61

They are always broken up into their elements

Question 62

What happens to a positive metal ion during electrolysis?

Answer 62

They are reduced to the element at the cathode

Question 63

What happens to the non-metal ions during electrolysis?

Answer 63

They are oxidised to the element at the anode

Question 64

How to use electrolysis to extract aluminium from bauxite

Answer 64

1) Bauxite contains aluminium oxide Al2O3 2) Aluminium oxide has a very high melting temperature so it's mixed with cryolite to lower the melting point 3) The molten mixture contains free ions - so it'll conduct electricity 4) The positive Al^3+ ions are attracted to the negative electrode where they pick up 3 electrons and turn into neutral aluminium atoms. They sink to the bottom of the electrolysis tank 5) Negative O2- ions are attracted to the positive electrode where they each lose 2 electrons. The neutral oxygen atoms will then combine to form O2 molecules

Question 65

What else do you have to factor when you electrolyse an aqueous solutions?

Answer 65

- The ions in the water - Hydrogen ions (H+) - Hydroxide ions (OH-)

Question 66

Ionic equation for water

Answer 66

H2O(l) H+(aq) + OH-(aq)

Question 67

What happens when a metal ions form an element that is more reactive than hydrogen during the process of electrolysis at the code in an aqueous solution?

Answer 67

If h+ ions and metal ions are present, hydrogen gas will ve produced

Question 68

At the anode, if OH- and halide ions are present, what forms?

Answer 68

- The halogens will be formed

Question 69

What happens at the cathode during electrolysis in an aqueous solution if the metal ions form an element that is less reactive than hydrogen?

Answer 69

A solid layer of the pure metal will be produced instead

Question 70

What happens at the anode if no halide ions are present?

Answer 70

The OH- ions are discharged an oxygen will be formed

Question 71

How to test for chlorine?

Answer 71

Damps litmus paper turning it white

Question 72

How to test for hydrogen?

Answer 72

Makes a "squeaky pop" with a lighted splint

Question 73

How to test for oxygen?

Answer 73

Relight a glowing splint

Question 74

What do half equations show?

Answer 74

The reactions at the electrodes (make sure that the number of electrons need to be the same for each half equation)