Topic 4 - Chemical Changes Flashcards
1
Q
what is an acid
A
a proton ( H+) donor
2
Q
what makes an acid an acid
A
the H+
3
Q
what is an alkaline
A
a proton acceptor (OH-)
4
Q
what makes an alkaline an alkaline
A
the OH-
5
Q
what happens in a neuralisation reaction
A
an acid and alkali react together, the hydrogen ions react with hydroxide ions to produce water
6
Q
what is the ionic equation for a neuralisation reaction between acid and alkali
A
H+ + OH- —> H2O
7
Q
what is the word equation for the neutralisation of acid and alkali
A
acid + base —> salt + water
8
Q
how do you find what volume of acid is needed to neutralise alkali
A
on a pH curve, find the pH 7 and draw a line across to the line then down to find the volume
9
Q
what does the pH scale measure
A
a measure of the acidity or alkalinity of a solution
10
Q
what does the pH scale go to
A
0-14
11
Q
how can pH be measured
A
using universal indicator or pH probe
12
Q
a solution with a pH of 7 is what?
A
neutral
13
Q
what is the pH of acid
A
less than 7
14
Q
what is the pH of alkaline
A
greater than 7
15
Q
what is universal indicator
A
a dye that changes colour depending on pH
16
Q
what is wide range indicator
A
contains a mixture of dyes that gradually change colour over a range of pH- its an estimate
17
Q
what happens during a displacement reaction
A
the more reactive metal displaces the less reactive metal
18
Q
what is shown in an ionic equation
A
only the particles that react and the products are shown
19
Q
what is a spectator ion
A
they don’t change in the reaction
20
Q
what is oxidation in terms of electrons
A
loss of electrons
21
Q
what is reduction in terms of electrons
A
gain of electrons
22
Q
what is the rhyme to remember oxidation and reduction in terms of electrons
A
Oxidation
Is
Loss
Reduction
Is
Gain
23
Q
what is the half equation for zinc
A
Zn –> Zn 2+ + 2e-
oxidation half equation- zinc loses electrons
24
Q
what happens to the metal ion and metal atom in a metal displacement reaction
A
the metal ion gains electrons- reduced
the metal atoms always loses electrons- oxidised
25
what is a metal ore
a rock containing enough metal or metal compound to make it worth extracting
26
what are native metals
found as the element because they are unreactive
eg platinum, gold, silver
27
what are most metals found as
compounds that require chemical reactions to extract
28
what are the stages of metal extraction
1. mine the rock
2. grind the rock to a powder
3. separate metal compound from waste(chemicals)
4. extract metal from compounds using reduction
29
how are metals less reactive than carbon extracted
can be extracted using carbon reduction in a blast furnace
30
why can carbon only be used to extract metals less reactive than them
carbon can only take oxygen from metals less reactive
31
what is an example of how iron reacts with carbon as a word equation
iron oxide + carbon --> iron + carbon dioxide
32
how are metals more reactive that carbon extracted
- using electrolysis
33
what is the problem with using electrolysis
expensive
34
why are some metals and products more expensive
they cost more to extract and have smaller amounts of metal in ore
35
how is tungsten extracted and why
by hydrogen reduction because carbon makes it too brittle
36
what is the equation for the reaction between metal and oxygen
what is this reaction?
metal + oxygen ---> metal oxides
oxidation because the metal gain oxygen
37
what is oxidation in terms of oxygen
gains oxidation in reaction
38
what is reduction in terms of oxygen
loss of oxygen in reaction
39
what is a reduction reaction
when a metal is separated from it oxide
40
how does potassium, sodium, lithium and calcium react with water
fizz, give of hydrogen, leaves alkaline solution of metal hydroxide
41
how does potassium, sodium, lithium react with dilute acid
explode
42
how does calcium react with dilute acid
fizz, give off hydrogen and form a salt
43
how does magnesium, aluminium, zinc and iron react with water
vey slow reaction
44
how does magnesium, aluminium, zinc and iron react with dilute acid
fizz, give off hydrogen, form a salt
45
how does tin and lead react with water
slight reaction with steam
46
how does tin and lead react with dilute acid
react slowly with warm acid
47
how does copper, silver and gold react with water
no reaction
48
how does copper, silver and gold react with dilute acid
no reaction
49
what does metal + oxygen produce
metal oxide
50
what does metal and acid produce
a salt + hydrogen
51
what does metal + water produce
metal hydroxide + hydrogen
52
what is the speed of reaction indicated by
by the rate at which the bubbles of hydrogen are given off
53
what is the reactivity series
a list of metals ranked in order of reactivity
54
what happens when metal reacts with other substances
the metal atoms form positive ions
55
what is the reactivity of a metal related to
its the tendency to form positive ions/ lose electrons
56
what happens the higher up the reactivity series
the higher up the series the more easy it will form positive ions so more reactive
57
what is often included in the reactivity series
carbon and hydrogen to give info about how metals react with them
58
what is the list of the reactivity series
potassium
sodium
lithium
calcium
magnesium
CARBON
zinc
iron
HYDROGEN
copper
59
how do you calculate the pH
1. find the concentration of acid
2. find the concentration of H+
3. find pH
60
ESQ calculate the pH of a solution of H2SO4 in which 0.0005 mol of H2 SO4 dissolved in 0.10dm3 of water
conc of acid= moles/volume= 0.0005/0.10= 5x10 -3 mol/dm3
conc of H += H2SO4 --> 2H+ + SO4 2-
5x10-3 --> 0.01 of H+
0.01= 1x10-2
pH=2
61
how can soluble salts be made
from acids by reacting them with solid insoluble substances eg. metal, metal oxides, hydroxides or carbonates
62
why is the solid added in excess to the acid
the solid is added to the acid in excess until it all reacts and the excess is filtered to produce a solution of salt
62
what happens if ammonia is bubbled through water
it dissolves to produce an alkaline solution
63
what is the method for making salts
1. gently warm the dilute acid using a Bunsen burner, then turn it off
2. add the insoluble base to the acid in excess to completely react all the acid-wait until it has fully reacted the excess will sink to bottom
3.filter out the excess solid to get a salt solution
4. to get pure solid crystals- gently heat the solution using a water bath/electric heater to evaporate some of the water
5. stop heating and leave to cool
6. crystals of the salt should form, they can be filtered out and dried
64
what is produced when acid+ metal carbonate base react
a salt + water + co2
65
what is produced when acid + ammonia solution reacts
salt+water
66
what is produced when metal and oxygen reacts
metal oxide
67
what is produced when metal and acid react
a salt + hydrogen
68
what is produced when metal and water react
metal hydroxide + hydrogen
69
what is the concentration
the concentration of an acid measures how much acid there is in a certain volume of water
70
the --- the amount of ---- in a volume, the more ------ the acid is
the larger the amount of acid in a volume, the more concentrated the acid is
71
what will happen to the pH with increasing acid concentration
the pH will decrease
72
you can have a ----- but ---- acid
you can have a strong but dilute acid
73
what is the pH of an acid or alkali
a measure of the concentration of H+ ions in the solution
74
ESQ the pH of a solution fell from pH 7 to pH 4. By what factor had the hydrogen ion concentration of the solution changed
difference= final pH-starting pH
4-7= -3
factor H+ ion changed=
10-(-3)= 103 or 1000
75
what is a strong acid
ionises(dissociates) completely in solution
76
what is a weak acid
only partially ionises in solution
77
because a weak acid only partially ionises, what does this mean
it is a reversible reaction
78
what are 3 examples of strong acids
- hydrochloric acid
- nitric acid
- sulfuric acid
79
what are 3 examples of weak acids
- ethanoic acid
- citric acid
- carbonic acid
80
what happens as the pH decreases by one unit
the H+ concentration of solution increase by a factor of 10
eg an acid of pH 4 has 10x conc of h+ ions of an acid of pH 5
81
what is electrolysis
breaking down or splitting up using electricity
82
what are electrolytes
liquids or solutions able to conduct electricity- molten or dissolved ionic compounds
83
why is it important the electrolytes are molten or dissolved
so the ions are free to move and it can conduct electricity
84
what is electrolysis used to extract
more reactive metals than aluminium
85
what is the process of electrolysis
- passing electric current through electrolytes cause the ions to move to the electrodes
- positively charged ions move to the negative electrode(cathode)
- negatively charged ions move to the positive electrode (anode)
- ions are discharged at electrodes producing elements
86
what is the rhyme to remember the electrodes
Postive
Anode
Negative
Cathode
ake
87
what is an electrode
a solid that conducts electricity and is submerged in the electrolyte
88
in copper chloride solution, which electrode does each one go to
copper- cu2+
chloride- cl-
copper-cathode
chloride- anode
89
what happens to the positive ions in the electrolyte
the positive ions move to the cathode and gain electrons(reduced)
90
what happens to the negative ions in the electrolyte
the negative ions moving to the anode lose electrons(oxidised)
91
what should the properties of the electrodes be
- high melting point
- unreactive
92
what are cations
positive ions
93
what are anions
negative ions
94
what happens to lead bromide during electrolysis
- bromine loses 1 electron each to form a Br2 molecule
- positive lead gains 2 electrons and becomes a lead atom- reduction
95
why does the electrode(anode) need to be replaced regularly
they are made of carbon so react with the oxygen produced to form CO2
96
when using aluminium what is produced at each electrode
cathode- aluminium
anode- produces oxygen
97
what is the problem with electrolysis
very expensive and requires lots of energy
98
how is aluminium manufactured
by the electrolysis of a molten mixture of aluminium oxide and cyolite
99
why is aluminium a mixture
aluminium oxide has a very high melting point- its mixed with cryolite to lower the melting point- uses less energy, so cheaper and less polluting
100
how do you predict with ions will discharge at the cathode
1. metal or hydrogen
2. if the metal is more reactive than hydrogen it will remain in solution and hydrogen gas will be produced
3. if metal is less reactive, a solid pure metal will be produced
101
how do you predict what ions will discharge at the anode
1. halides(cl-,Br-,L-) molecules chlorine ,bromine or iodine formed
2. hydroxide (OH-) and oxygen produced
3. other negative ions
102
what is important when writing half equations
same number of atoms/ions on either side
- charge on either side is equal
103
what does a half equation show
show reactions at the electrodes
104
at the cathode, hydrogen produced unless metal is more reactive
at the anode, oxygen is produced unless halide ions are there
- why does this happen
in the solution, water molecules break down and produce hydrogen/hydroxide ions that are discharged
105
what is present in every aqueous solutions
OH- and H+
106
when copper sulphate is electrolysed what is produced at each electrode
anode- no halide ions so oxygen + water are produced
cathode- copper is less reactive than hydrogen so copper is produced
107
when sodium chloride solution is electrolysed what is produced at each electrode
anode- chloride ions are present so chlorine gas produced
cathode- sodium is more reactive than H+ so hydrogen gas is formed
108
what is the test for hydrogen
produces 'squeaking pop' from lit splint
109
what is the test for oxygen
relights a glowing splint
110
what is the test for chlorine
turns damp blue litmus paper red, then bleaches it
