Chemical changes Flashcards
(133 cards)
1
Q
What is the pH scale
A
a measure of how acidic or alkaline a substance is
2
Q
the lower the pH scale..
A
the more acidic it is
3
Q
the higher the pH scale…
A
the more alkaline it is
4
Q
What is the pH of a neutral substance
A
pH 7
5
Q
pH of car battery acid and stomach acid
A
car battery acid = 1
stomach acid = 2
6
Q
pH of vinegar , lemon juice
A
3
7
Q
pH of acid rain
A
4
8
Q
pH of normal rain
A
5/6
9
Q
pH of pure water
A
7
10
Q
pH of washing up liquid
A
9
11
Q
pH of pancreatic juice
A
10
12
Q
pH of soap powder
A
11
13
Q
pH of bleach
A
12
14
Q
pH of caustic soda(drain cleaner)
A
13/14
15
Q
What is an indicator
A
a dye that changes colour depending on wether it is above or below a certain pH
16
Q
What are wide range indicators
A
contain a mixture of dyes so gradually change colour over a broad range of pH
17
Q
what are wide range indicators useful for
A
estimating the pH of a solution
18
Q
An example of a wide range indicator
A
Universal indicator
19
Q
What colours does a universal indicator have on its pH scale
A
-classic colours
-red for acid goes yellower then to green for neutral
-then darker to blues and purples
20
Q
What is a more accurate way to measure pH than an indicator
A
pH probe attached to a pH meter
-as it gives it as a numerical number rather than a colour
21
Q
What does a pH probe attached to a pH meter do
A
-be used to measure pH electronically
-the probe is placed in the solution u are measuring and the pH is given on a digital display as a numerical number
22
Q
What is acid as a substance
A
-a substance that forms aqueous solutions with a pH of less than 7
23
Q
What ions do acids form in water
A
H+ ions
24
Q
what is a base
A
a substance with a pH greater than 7
25
What is an alkali
a base that dissolves in water to form a solution with a pH greater than 7
26
what ions do alkalis form in water
OH- ions
27
What is the reaction between acids and bases called
neutralisation
28
What is the word equation for a neutralisation reaction
acid+base ---> salt + water
29
What is the symbol equation for a neutralisation reaction
H+ (aq) + OH- (aq) ---> H2O (l)
30
what are the products of a neutralisation reaction
the products are neutral ,have a pH 7
31
how can we know if a neutralisation reaction is over
an indicator can be used
32
What do acids do in aqueous equations
-they ionise
-they produce hydrogen ions H+
33
What do strong acids do in water
-ionise completely
-all acid particles dissociate to release H+ ions
34
Examples of strong acids
sulfuric, hydrochloric and nitric acids
35
What do weak acids do in water/solution
-do not fully ionise
-only a small proportion of acid particles dissosiate to release H+ ions
36
Examples of weak acids
-ethanoic, citric and carbonic acids
37
What type of reaction is the ionisation of a weak acid
- a reversible reaction which sets up an equilibrium between the undissociated and dissociated acid
38
Where does the position of equilibrium lie of the ionisation of a weak acid
since only a few of the acid particles release H+ ions
-the position of the equilibrium lies well to the left
39
What do the reactions of acids involve
the H+ ions reacting with other substances
40
If the concentration of H+ ions is higher...
-the rate of reaction will be faster
-so strong acids will be more reactive than weak acids of the same concentration
41
What is the pH of an acid or alkali based off
the measure of the concentration of H+ ions in the solution
42
what happens for every decreased of 1 on the pH scale
the concentration of H+ ions increases by a factor of 10
43
Compare the pH of a strong and weak acid
the pH of a strong acid is always less than the weak acid if they have the same concentration
44
So what is acid strength
tells u what proportion of the acid molecules ionise in water
45
But what is the concentration of an acid
DIFFERENT to strength
-measures how much acid there is in a certain volume of water
46
the larger the amount of acid in a certain volume of water...
the more concentrated the acid is
47
So what combinations of strength and combination for acids can u have
can have a dilute but strong acid
-or a concentrated but weak acid
48
What will happen to the pH with increasing acid concentration
the pH will decreased
-regardless of wether it is a strong or weak acid
49
What are metal oxides and metal hydroxides
-soluble compounds which are alkalis
-dissolve in water
50
what do bases that don't dissolve in water do with acids
can still take part in neutralisation reactions with acids
51
So what can all metal oxides and metal hydroxides react with
-acids
to form a salt and water
52
word equation for metal oxides or metal hydroxides reacting with acids
acid+metal oxide --> salt+ water
acid+ metal hydroxide--> salt+water
53
what salt is produced with the reaction of metal oxides or metal hydroxides reacting with acids
the salt produced depends upon the acid and the metal ion in the oxide or hydroxide
54
Example of the salt produced with sulfuric acid and potassium hydroxide
potassium sulfate is made
55
Example of the salt produced with hydrochloric acid and copper oxide
copper chloride
56
What are metal carbonates
are also bases
57
What do metal carbonates produce in a reaction with acid
-salt
-water
-carbon dioxide
58
word equation for metal carbonates reacting with acid
acid+ metal carbonate --> salt+ water+ carbon dioxide
59
How can u make soluble salts
using an insoluble base and acid
60
What is the reactivity series
-lists metals in order of their reactivity towards other substances
61
How are metals reactivity determined
is determined by how easily they lose electrons -forming positive ions
62
So the more easily a metal forms positive ions...
the higher a metal is on the reactivity series
63
What is the order further based off
-if u compare the relative reactivity of dif metals with either an acid or water
-then put them in order from the most reative to least
then u get the reactivity series
64
What do some metals react with acids to produce
a salt and hydrogen gas
65
equation for acid reacting with metal
acid+metal --> salt+hydrogen
66
What is the speed of reacton indicated by
-the rate at which the bubbles of hydrogen are given off
67
What does copper not react with
won't react with cold dilute acids
68
examples of very reactive metals
-potassium,sodium,lithium, calcium all react expolsively
69
examples of less reactive metals
magnesium,xinc and iron react less violently
70
which non metals are included for reference in the reactivity series
-carbon
-hydrogen
71
How can u investigate the reactivity of metals
-by measuring the temperature change of the reaction with an acid or water over a set time period
-the more reactive the greater the temp change
72
What do the reactions of metals with water also show
the reactivity of metals
73
What metals will all react with water
potassium ,sodium, lithium and calcium
74
Which less reactive metals will not react with water
zinc,iron and copper
75
equation for metal reacting with water
metal+ water --> metal hydroxide+ hydrogen
76
How to get metals from the earth
have to extract them from a compound
77
What are the 2 different ways to extract a metal
-reduction
-electroylsis
78
What are lots of metals found as in ores
-oxides (process from oxidation, react with oxygen)
-seen with iron and aluminium
79
What is the reaction that seperates a metal from its oxide
called a reduction reaction
80
Formation of a metal ore
oxidation=gain of oxygen
81
equation of oxidation
2Mg + O2 --> 2MgO
82
Extraction of metal
Reduction= loss of oxygen
83
Equation for reduction
2CuO + C --> 2Cu + CO2
84
How can other metals be reducted
can be extracted from their ores chemically by reduction using carbon
85
What happens to the carbon in a reduction reaction
the carbon is oxidised
86
When can metals not be reducted with ion
-the metals higher than carbon in the reactivity series have to be extracted using electrolysis
which is expensive
87
When can metals be extracted by reduction
-the metals below carbon in the reactivity series can be extracted by redcution using carbon
88
What are the 3 metals that can be extracted with carbon
-Zinc
-Iron
-Copper
89
Why can carbon only be used for those metals
as carbon can only take oxygen away from metals which are less reactive than carbon itself
90
How are unreactive metals (eg.native metals) extracted from earth
-so unreactive that they are in the earth as the metal itself
-eg. gold is mined as its elemental form
91
What is oxidation in electrons
loss of electrons
92
What is reduction in electrons
gain of electrons
93
mnemonic for oxidation and reduction w/ electrons
OIL RIG
94
What are redox reactions
Reduction and Oxidation happen at the same time
95
Oxidation written example
Fe - 2e- --> Fe2+
96
Reduction written example
2H+ + 2e- --> H2
97
What are displacement reactions
a more reactive metal will displace a less reactive metal from its compound
98
What happens if u put a reactive metal into the solution of a dissolved metal compound
the reactive metal will replace the less reactive metal in the compound
99
In a displacement reaction what is oxidised and reduced
-the metal ion that gains electrons and is reduced
-the metal atom always loses electrons and is oxidised
100
What is shown in an ionic equation
-only the particles that react and the products they form are shown
101
What are spectator ions
-ones that don't change in the reaction
-no interest here so can be crossed out
102
So what does the ionic equation for displacement concentrate on
the substances that are being oxidised or reduced
103
What does electrolysis use to cause a reaction
an electrical current
104
What happens during electrolysis
an electric current is passed through an electrolyte
-the ions move towards the electrodes,where they react, and the compound decomposes
105
What is an electrolyte
a molten or dissolved ionic compound
106
What happens to the positive ions in the electrolyte
they will move towards the cathode(- electrode) and gain electrons (they are reduced)
107
What happens to the negative ions in the electroylte
will move towards the anode ( + electrode) and lose electrons (they are oxidised)
108
so what is the charge through the electroylte
a flow of charge as ions travel to the electrodes
109
What happens as ions gain or lose electrons (electrolysis)
they form the uncharged element and are discharged from the electrolyte
110
Why can't an ionic solid be electrolysed
because the ions are in fixed positions and can't move
111
Why can molten ionic compounds be electrolysed
because the ions can move freely and conduct electricity
112
What are molten ionic liquids made of
are always broken up into their elements eg. lead bromide
113
Equation for a positive metal ions being reduced to the element at the cathode
Pb2+ + 2e- ---> Pb
114
Equation for a negative non metal ions being oxidised to the element at the anode
2Br- ---> Br2 + 2e-
115
Why is electrolysis an expensive method
as lots of energy is required to melt the ore and produce the required current
116
What is Aluminium extracted from
the ore bauxite by electroylsis
the ore contains aluminium oxide
117
What is aluminium's melting temp
very high
118
How are high melting points reduced so there is a cheaper electrolysis
mixed with cryolite to lower the melting point
119
What are the positive Al3+ ions attracted to (electrolysis)
-attracted to the negative electrode
-where they each pick up 3 electrons and turn into neutral aluminium atoms
-sink to the bottom of tank
120
What are the negative O2- ions attracted to
-the positive electrode
-where they each lose 2 electrons
-the neutral oxygen atoms will then combine to form O2 molecules
121
Photo of electrolysis with aluminium oxide
122
What will there be in an aqueus solution (electrolysis)
-as well as the ions from the ionic compound there will be hydrogen ions (H+) and hydroxide ions (OH-) from the water
123
What will happen at the cathode if H+ ions and metal ions are present
hydrogen gas will be produced if the metal ions form an elemental metal that is more reactive than hydrogen
124
What will happen at the cathode if H+ ions and less reactive metal ions are present
-if the metal ions form an elemental metal that is less reactive than hydrogen a solid layer of the pure metal will be produced instead
125
What will happen at the anode if OH- and halide ions are present
-molecules of chlorine, bromine and iodine will be formed
-if no halide ions are present then the OH- ions are discharged and oxygen will be formed
126
Test for chlorine
Chlorine bleaches damp litmus paper turning it white
127
Test for hydrogen
hydrogen makes a squeaky pop with a lighted splint
128
Test for oxygen
oxygen will relight a glowing splint
129
What do half equations show
the reactions at the elctrodes
-the number of electrons need to be the same for each one
130
Negative electrode half equation for aqueaus sodium chloride
2H+ + 2e- ---> H2
131
Positive electrode half equation for aqueaus sodium chloride
2Cl- - 2e- ---> Cl2
132
Why are the electrons on either side of the half equation balanced
so they can be canclled out in the full ionic equation
133
When halide isn't present in the aqueaus solution the half equation for the anode is
4OH- --> O2 + 2H20 + 4e-
