Chemical Changes Flashcards
(105 cards)
1
Q
Range of pH scale
A
0 to 14
2
Q
What is lower on pH scale
A
More acidic solutions
3
Q
What is higher on pH scale
A
More alkaline solutions
4
Q
pH of neutral substances
A
7
5
Q
What do you use to measure pH of a solution
A
An indicator
6
Q
Indicator
A
Dye that changes colour depending on whether it’s above or below a certain pH
7
Q
Wide range indicator
A
Indicator that contains a mixture of dyes so they gradually change colour over a broad range of pH
8
Q
Example of wide range indicator
A
Universal indicator
9
Q
Colour of acidic solutions on universal indicator
A
Orange-red
10
Q
Colour of alkaline solution on universal indicator
A
Blue-purple
11
Q
Colour of neutral solution on universal indicator
A
Green
12
Q
How to measure pH electronically
A
- pH probe and pH meter
- probe placed in solution, meter gives numerical value of pH
13
Q
More accurate method of measuring pH
A
pH probe and pH meter
14
Q
Why is pH probe and meter more accurate
A
- gives numerical reading
- observing colour is subjective
15
Q
Acid
A
Substance that forms aqueous solutions with pH less than 7
16
Q
What ions do acids form in water
A
H⁺
17
Q
Base
A
A substance with pH greater than 7
18
Q
Alkali
A
Base that dissolves in water to form a solution with pH greater than 7
19
Q
What ions do alkalis form in water
A
OH⁻
20
Q
Neutralisation
A
Reaction between acid and base
21
Q
Neutralisation reaction word equation
A
acid + base —> salt + water
22
Q
Neutralisation reaction between acids and alkalis symbol equation
A
H⁺ + OH⁻ —> ‘salt’ + H₂O
23
Q
What happens when an acid/alkali neutralise each other
A
Products will be neutral with pH 7
24
Q
What happens to strong acids in water
A
- ionise completely in an aqueous solution
- all acid particles dissociate to release H⁺ ions
25
Examples of strong acids + chemical formulas
- hydrochloric - HCl
- nitric - H₂SO₄
- sulfuric - HNO₃
26
What happens to weak acids in water
- do not fully ionise
- small proportion of acid particles dissociate to release H⁺ ions
27
Examples of weak acids
- carbonic
- citric
- ethanoic
28
Is ionisation of weak acids reversible
Yes
29
Why is ionisation of weak acids reversible
- reaction sets up equilibrium between undissociated + dissociated acid
- few acid particles release H⁺ = equilibrium position lies to left
30
Which kind of acid is more reactive
Stronger ones
31
Why are stronger acids more reactive
Higher concentration of H⁺ ions increases reactivity
32
pH
Measure of concentration of hydrogen (H⁺) ions in a solution
33
How H⁺ ion concentration change as pH changes
- pH decrease 1 = conc X10
- pH increase 1 = conc ÷10
34
Acid strength
Proportion of acid molecules that ionise in water
35
Acid concentration
How much acid there is in a certain volume of water
36
How does acid concentration affect pH
pH decreases as acid concentration increases
37
Metal bases
- metal oxide
- metal hydroxide
- metal carbonate
38
Do metal oxides dissolve in water
Yes
39
Do metal hydroxides dissolve in water
Yes
40
Acid + metal oxide --->
Salt + water
41
Acid + metal hydroxide --->
Salt + water
42
Acid + metal carbonate --->
Salt + water + carbon dioxide
43
Metal + oxygen
Metal oxide
44
Making salts practical
- pick right acid and insoluble base
- gently warm dilute acid with Bunsen burner, turn off
- add insoluble base to acid a bit at a time until no more reacts - base is in excess and sinks to bottom of flask after stirring as all acid has been neutralised
- filter out excess solid to get salt solution
- pure/solid salt crystals - gently heat solution in water bath to evaporate some water, stop, leave solution to cool, crystals form to be filtered + dried
45
What is reactivity series
List of metals in order of reactivity towards other substances
46
Reactivity series
- potassium
- sodium
- lithium
- calcium
- magnesium
- aluminium
- carbon
- zinc
- iron
- tin
- lead
- hydrogen
- copper
- silver
- gold
- platinum
47
What determines reactivity of metals
How easily they lose electrons - forming positive ions
48
What happens when metals react with water or acid
Lose electrons - forming positive ions
49
Methods of finding reactivity of metals
- react with acid
- react with water
- measure reaction temperature change
50
Acid + metal --->
Salt + hydrogen
51
What indicates reactivity of metal when reacted with acid
- hydrogen bubbles given off faster means faster rate of reaction
- which means more reactive
52
What metals react explosively with acid
- potassium
- sodium
- lithium
- calcium
53
What metals react less violently with acid
- magnesium
- zinc
- iron
54
Which metal doesn't react with cold, dilute acid
Copper
55
Metal + water --->
Metal hydroxide + hydrogen
56
What metals will react with water
- potassium
- sodium
- lithium
- calcium
57
What metals won't react with water
- zinc
- iron
- copper
58
How can reactivity be found with temperature change
- react metal with acid/water
- greater temperature change = more reactive
59
Oxidation in terms of oxygen
Gain of oxygen
60
Reduction in terms of oxygen
Loss of oxygen
61
How are most metals found
- oxidised by air
- **metal oxide** found in ore
62
Ore
Rock containing metals compounds
63
How can some metal oxides be extracted by reduction with carbon
- metal reacted with carbon
- ore is reduced as oxygen is removed from it
- carbon gains oxygen and is oxidised to form carbon dioxide
64
How is gold found
As an unreactive metal that is found in the Earth as the metal itself
65
How metals like gold extracted
Mined in elemental form
66
Which metals are extracted by electrolysis
Metals above carbon on reactivity series
67
Which metals are extracted by reduction using carbon
Metals below carbon on reactivity series
68
Why are some elements mined in elemental form
They are so unreactive
69
Oxidation in terms of electrons
Loss of electrons
70
Reduction in terms of electrons
Gain of electrons
71
Species
An atom, ion or molecule
72
Redox reaction
Reaction where reduction and oxidation happen at the same time, transferring electrons
73
Displacement reaction
Redox reaction where a more reactive metal displaces a less reactive metal from its compound
74
Formula for displacement reactions
More reactive + less reactive in compound --> more reactive in compound + less reactive
75
Why are displacement reactions redox reactions
- metal ion gains electrons - reduced
- metal atom loses electrons - oxidised
76
How to write ionic equation
- write full equation
- add charges to full equation
- remove ions that charges change (spectator ions)
77
How to write half equation from ionic equation
- take only element you are writing it for
- add electrons to one of the sides so both sides charges are neutral
78
Electrolysis equipment
- beaker
- electrolyte solution
- anode
- cathode
- wire + power source
79
Electrolyte solution
Liquid/solution containing ionic compound - electrons free to move and go to respective electrode
80
Electrodes
Solid conductors
81
Anode charge
Positive
82
Cathode charge
Negative
83
Purpose of power source in electrolysis
Drives flow of electrons through wire, between electrodes
84
What does electrolysis mean
Splitting up with electricity
85
Versions of electrolysis
- electrolysis of molten substance
- electrolysis of aqueous solution
86
How does electrolysis split up molten compounds
- electric current flows through electrolyte
- ions attracted to electrodes
- ions discharged at electrodes
87
What happens at anode
Oxidation
88
What happens at cathode
Reduction
89
Which process occurs first in electrolysis
Oxidation
90
What happens after oxidation in electrolysis
Electrons travel through wire from anode to cathode for reduction
91
Why is it preferable to extract metals through displacement with carbon
Cheap
92
Downsides of electrolysis
Requires much energy so **expensive**
93
Chemical formula for aluminum oxide
Al₂O₃
94
Why is aluminum oxide not ready for electrolysis straight away
- electrolysis needs ions free to move
- aluminum oxide solid - ions fixed
95
How to prepare aluminum oxide for electrolysis
- **purify** bauxite into Al₂O₃
- mix Al₂O₃ with cryolite mineral - lowers melting point
- **melt** Al₂O₃ to become molten - ions free to move
96
When is electrolysis of aqueous solution used, why
When substance being separated is soluble - dissolved in water (easy to do)
97
What does water split up into in a solution
- H⁺ ions
- OH⁻ ions
98
Which ions from water go to anode
OH⁻
99
Which ions from water go to cathode
H⁺
100
Aqueous electrolysis rules at anode
- group 7 metal - gets discharged
- NO group 7 metal - OH⁻ gets discharged
101
Aqueous electrolysis rules at cathode
Least reactive gets discharged
102
H⁺ half equation
2H⁺ + 2e⁻ --> H₂
103
OH⁻ half equation
4OH⁻ --> 2H₂O + O₂ + 4e⁻
104
Reduction half equation
ion + electrons --> discharged
105
Spectator ion
Ion doesn't take part in reaction - keeps same charge
