Chemical Changes Flashcards
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 indicator
14
Q
Acid
A
Substance that forms aqueous solutions with pH less than 7
15
Q
What ions do acids form in water
A
H⁺
16
Q
Base
A
A substance with pH greater than 7
17
Q
Alkali
A
Base that dissolves in water to form a solution with pH greater than 7
18
Q
What ions do alkalis form in water
A
OH⁻
19
Q
Neutralisation
A
Reaction between acid and base
20
Q
Neutralisation reaction word equation
A
acid + base —> salt + water
21
Q
Neutralisation reaction between acids and alkalis symbol equation
A
H⁺ + OH⁻ —> H₂O
22
Q
What happens when an acid/alkali neutralise each other
A
Products will be neutral with pH 7
23
Q
What happens to strong acids in water
A
- ionise completely in an aqueous solution
- all acid particles dissociate to release H⁺ ions
24
Q
Examples of strong acids + chemical formulas
A
- hydrochloric - HCl
- nitric - H₂SO₄
- sulfuric - HNO₃
25
What happens to weak acids in water
- do not fully ionise
- small proportion of acid particles dissociate to release H⁺ ions
26
Is ionisation of weak acids reversible
Yes
27
Why is ionisation of weak acids reversible
- reaction sets up equilibrium between undissociated and dissociated acid
as only a few acids particles release H⁺, equalibrium position lies well to left
28
Which kind of acid is more reactive
Stronger ones
29
Why are stronger acids more reactive
Higher concentration of H⁺ ions increases reactivity
30
pH
Measure of concentration of hydrogen (H⁺) ions in a solution
31
Formula for factor of change in H⁺ ion concentration
Factor H⁺ ion concentration changes by = 10⁻ˣ
X = change in pH
32
Acid strength
Proportion of acid molecules that ionise in water
33
Acid concentration
How much acid there is in a certain volume of water
34
How does acid concentration affect pH
pH decreases as acid concentration increases
35
Metal bases
- metal oxide
- metal hydroxide
- metal carbonate
36
Do metal oxides dissolve in water
Yes
37
Do metal hydroxides dissolve in water
Yes
38
Acid + metal oxide --->
Salt + water
39
Acid + metal hydroxide --->
Salt + water
40
Acid + metal carbonate --->
Salt + water + carbon dioxide
41
Metal + oxygen
Metal oxide
42
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
43
What is reactivity series
List of metals in order of reactivity towards other substances
44
Reactivity series
- potassium
- sodium
- calcium
- magnesium
- aluminium
- carbon
- zinc
- iron
- tin
- lead
- hydrogen
- copper
- silver
- gold
- platinum
45
What determines reactivity of metals
How easily they lose electrons - forming positive ions
46
What happens when metals react with water or acid
Lose electrons - forming positive ions
47
How are most metals extracted
Found as compounds, extracted through chemical reactions
48
How is gold found
As an unreactive metal that is found in the Earth as the metal itself
49
Acid + metal --->
Salt + hydrogen
50
What indicates speed of reaction between acid and metal
Rate at which bubbles of hydrogen are given off
51
How to more reactive metals react
- faster
- explosively
52
How do less reactive metals react
- slower
- less violently
53
Metal + water --->
Metal hydroxide + hydrogen
54
Which metals will react with water
More reactive ones
55
Oxidation in terms of oxygen
- metals reacting with oxygen to form oxides
- gain of oxygen
56
Reduction in terms of oxygen
- reaction that separates a metal from it's oxide
- loss of oxygen
57
How can some metals 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
58
Which metals are extracted by electrolysis
Metals above carbon on reactivity series
59
Which metals are extracted by reduction using carbon
Metals below carbon on reactivity series
60
Why are some elements mined in elemental form
They are so unreactive
61
Oxidation in terms of electrons
Loss of electrons
62
Reduction in terms of electrons
Gain of electrons
63
Redox reaction
Reaction where reduction and oxidation happen at the same time, transferring electrons
64
Displacement reaction
Redox reaction where a more reactive metal displaces a less reactive metal from its compound
65
Why are displacement reactions redox reactions
- metal ion gains electrons - reduced
- metal atom loses electrons - oxidised
66
Electrolysis equipment
- beaker
- electrolyte solution
- anode
- cathode
- wire + power source
67
Electrolyte solution
Liquid/solution containing ionic compound - electrons free to move
68
Electrodes
Solid conductors
69
Anode charge
Positive
70
Cathode charge
Negative
71
What does electrolysis mean
Splitting up with electricity
72
Versions of electrolysis
- electrolysis of molten substance
- electrolysis of aqueous solution
73
How does electrolysis split up molten compounds
- electric current flows through electrolyte
- ions attracted to electrodes
- ions discharged at electrodes
74
What happens at anode
Oxidation
75
What happens at cathode
Reduction
76
Which process occurs first in electrolysis
Oxidation
77
What happens after oxidation in electrolysis
Electrons travel through wire from anode to cathode for reduction
78
Why is it preferable to extract metals through displacement with carbon
Cheap
79
Downsides of electrolysis
Requires much energy so **expensive**
80
Why is aluminum oxide not ready for electrolysis straight away
- electrolysis needs ions free to move
- aluminum oxide solid - ions fixed
81
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
82
When is electrolysis of aqueous solution used
When substance being separated is soluble - dissolved in water (easy to do)
83
What is always present from water in electrolysis of aqueous soltion
- H⁺ ions
- OH⁻ ions
84
Which ions from water go to anode
OH⁻
85
Which ions from water go to cathode
H⁺
86
Aqueous electrolysis rules at anode
- group 7 metal - gets discharged
- NO group 7 metal -OH⁻ gets discharged
87
Aqueous electrolysis rules at cathode
Least reactive gets discharged
88
H⁺ half equation
2H⁺ + 2e⁻ --> H₂
89
OH⁻ half equation
4OH⁻ --> 2H₂O + O₂ + 4e⁻
90
Reduction half equation
ion + electrons --> discharged
91
Oxidation half equation
discharged --> ion + electrons
