Topic 4- Chemical changes Flashcards
1
Q
what does the ph scale go from
A
0 to 14
2
Q
what is the ph scale a measure of
A
how acidic or alkaline a solution is
3
Q
the lower the ph…
A
the more acidic it is
4
Q
the higher the ph….
A
the more alkaline it is
5
Q
what pH does a neutral substance have (water)
A
7
6
Q
whats an indicator
A
a dye which changes colour depending on whether its above or below a certain pH
7
Q
what are wide range indicators
A
indicators that contain a mixture of dyes that means thry gradually change colour over a broad range of pH (universal indicator)
8
Q
give an example of electronic indicating
A
a pH probe attatched to a pH meter is placed in the solution you are measuring and the pH is given on a digital display as a numerical value, meaning its mre accurate than an indicator
9
Q
what ions do acids form in water
A
H+
10
Q
whats an alkali
A
a base that dissolves in water to form a solution with a ph greater than 7
11
Q
give the numbers on the pH scale for an acid
A
less than 7
12
Q
give the numbers on the pH scale for a base
A
greater than 7
13
Q
what ions do alkalis form
A
OH -
14
Q
whats an acid
A
a substance that forms aqueous solutions will a pH of less than 7
15
Q
whats the reaction between acids and bases called
A
neutralisation
16
Q
give the word equation for acids and bases
A
acid + base -> salt + water
17
Q
give the symbol equation for acids and bases
A
H+ (aq) + OH- (aq) -> H2O (l)
18
Q
when acid neutralises a base
A
the products are neutral and at pH7
19
Q
what can an indicator show
A
that a neutralisation is over
20
Q
what does an acid and alkali produce
A
water
21
Q
what do acids produce in water
A
protons (hydrogen ions)
22
Q
what do acids do in aqueous solutions
A
ionise
23
Q
whats a H+ ion also known as
A
a proton
24
Q
what do strong acids do in water
A
ionise completely
all acid particles dissociate to release H+ ions
25
name some strong acids
sulfuric, hydrochloric, nitric acids
26
name some weak acids
ethanoic, citric and carbonic
27
what do weak acids do in a solution
do not fully ionise and only a small proportion of acid particles dissociate to release H+ ions
28
describe the ionisation of a weak acid
reversible reaction
| sets up equilibrium between the undissociated and dissociated acid
29
why does the position of equilibrium lie on the left in the ionisation of weak acids
because only a few of the acid particles release H+ ions
30
what do reactions of acids involve
the H+ ions reacting with other substances
31
if the conc of H+ ions is higher...
the rate of reaction will be faster
32
which are more reactive, strong acids or weak acids?
strong will be more reactive than weak acids of the same concentration
33
whats pH a measure of in terms of ion s
the conc of hydrogen ions (H+) in a solution
34
describe the ratio between the ions and the pH scale
for every decrease of 1 on the pH scale, the conc of H+ ions increases by a factor of 10
for a decrease of 2 on the pH scale, the conc of H+ ions increases by a factor of 100
35
give the equation for the factor H+ ion concentration change
factor H+ ion concentration changes by = 10-x (to the power of)
36
whats x?
the difference in pH
| so if pH falls from 7 to 4 the difference is 3- and the factor the H+ ion conc has increased by is 10- (-3) = 10(3)
37
what does acid strength tell you
what proportion of the acid molecules ionise in water
38
what does concentration tell you
measures how much acid their is in a certain volume of water (how watered down your acid is)
39
whats the relationship between amount of acid and concentration
the larger the amount of acid there is in a certain colume of liquid, the more concentrated the acid is
40
what will the pH do with acid, regardless of the acid strength
decrease with increasing acid conc
41
what are metal oxides and metal hydroxides
bases
42
describe metal oxides and metal hydroxides
some dissolve in water
soluble
alkalis
43
give the two equations for metal oxides and metal hydroxides
metal oxide + acid -> salt + water
| metal hydroxide + acid -> salt + water
44
what would sulfuric acid + potassium HYDROXIDE produce
potassium sulfate + water
| H2SO4 + 2KOH -> K2SO4 + 2H20
45
what are metal carbonates
bases
46
give the equation for metal carbonates
acid + metal carbonate -> salt + water + carbon dioxide
47
what would hydrochloric acid + sodium carbonate produce
sodium chloride + water + carbon dioxide
48
you can make soluble salts using an..
insoluble base
49
if you wanted to make copper chloride what could you mix
copper oxide and hydrochloric acid
50
how do you make soluble salts from an insoluble base (practical)
1) gently warm dilute acid using bunsen burner, then turn off burner
2) add insoluble base to acid a bit at a time until no more reacts ( the base is in excess)
3) stop stiring when solid is sinking to to bottom (its excess)
4) filter out excess solid to get salt solution
5) to get the pure, solid crystals of salt, gently heat solution using a water bath or electric heater to evaporate some of the water ( make it more conc)
6) stop heating and leave to cool
7) crystals should form which can be filtered out of solution and then dried ( crystalisation)
51
what does the reactivity series list
metals in order of their reactivity towards other metals
52
what is a metals reactivity determined by
how easily they lose electrons to form positive ions
53
the higher a metal is in the reactivity series...
the more easily it reacts with water or acid
54
give the word equation for acid + metal
acid + metal -> salt + hydrogen
55
whats the speed of a reaction indicated by
the rate at which the bubbles of hydrogen are given off
56
the more reactive the metal....
the faster it will be
57
how does magnesium react will cold dilute acids
vigorously, produces lots of bubbles
58
how do zinc and iron react which dilute acids
slowly, but more strongly if you heat them up
59
Fe + 2HCl -> ......
FeCl + H2
60
how else can you investigate the reactivity of metals
by measuring the temperature change of the reaction with an acid or water over a set time period. if you use the same mass and surface area of metal each time, then the more reactive the metal, the greater the temp change should be
61
give the word equation for metal + water
metal + water -> metal hydroxide + hydrogen
62
Ca (s) + 2H20 (l) -> ....
Ca(OH)2 (aq)+ H2 (g)
63
which metals will react with water
potassium, sodium, lithium, calcium
ZINC IRON AND COPPER WONT
64
where do metals often have to be extracted from
their oxides
65
whats a reaction where a metal is separated from its oxide called
a reduction reaction
66
whats oxidation
gain of oxygen
| e.g. magnesium is oxidised to make magnesium oxide 2Mg + O2 -> 2MgO
67
whats reduction
loss of oxygen
e.g. copper oxide is reduced to copper
2Cu + C -> 2Cu + CO2
68
how can zinc iron and copper be extracred from their ores
by reduction using carbon
69
what happens in a reduction using carbon
the ore is reduced as oxygen is removed from it and carbon gains oxygen so is oxidised
70
give an example of reduction using carbon
iron oxide + carbon -> iron + carbon dioxide
71
how are potassium, sodium lithium calcium and magnesium extracted
using electrolysis
72
why can zinc iron and copper be extracted by reduction using carbon
because theyre lower than carbon in the reactivity series
73
give an example of a metal that is so unreactive its found in the earth as itself
gold
74
whats a radox reaction,
where electrons are transferred
75
describe oxidation and reduction in terms of electrons
loss of electrons- oxidation
| gain of electrons- reduction
76
when do reduction and oxidation happen
at the same time
77
Al > Al3+ 3e- reduction or oxidation?
oxidation because Al has lost its electrons
78
O + 2e- > O2- reduction or oxidation?
reduction because oxygen has gained electrons
79
give the rule for displacement
a more reactive metal will displace a less reactive metal from its compound
80
finish the equation
| iron + copper sulfate ->
iron sulfate + copper
| BECAUSE IRON IS MORE REACTIVE THAN COPPER
81
for this reaction work out the two half equations...
Fe + CuSO4 > FeSO4 + Cu
iron + copper sulfate > iron sulfate + copper
Fe loses two electrons to become 2+
Cu gains two electrons to become 2-
Fe > Fe2+ 2e-
Cu2+ + 2e- > Cu
82
whats oxidation
Gains Oxygen (as the name suggests)
Loses Hydrogen
Loses Electrons
83
whats reduction
Loses Oxygen
Gains Hydrogen
Gains Electrons
84
what does electrolysis mean
splitting up with electricity
85
what happens in electrolysis
an electric current is passed through an electrolyte and the ions move towards the electrodes, where they react and the compound decomposes
86
whats an electrolyte
a molten or dissolved ionic compound
87
what happens to the positive ions in electrolysis
the positive ions in the electrolyte will move towards the cathode (-) and gain electrons
THEY ARE REDUCED
88
what happens to the negative ions in electrolysis
the negative ions in the electrolyte will move towards the anode (+) and lose electrons
THEY ARE OXIDISED
89
what does the movement of ions create
a flow of charge through the electrolyte as ions travel to the electrodes
90
as ions gain or lose electrons...
they form the uncharged element and are discharged from the electrolyte
91
why cant an ionic solid be electrolysed
because the ions are in fixed positions and cant move
92
why can molten ionic compounds be electrolysed
because the ions can move freely and conduct electricity
93
what do positive metal ions do at the cathode
they are reduced as they gain electrons
94
what do negative non metals do at the anode
they are oxidised as they lose electrons
95
describe the electrolysis which will take place with aluminium being extracted form bauxite...
1) aluminium has a very high m temp so its mixed with cryolite to lower the mpoint
2) the molten mixture contains free ions so it will conduct electricity
3) the positive Al3+ ions are attracted to the negative electrode where they each pick up three electrons and turn into neutral aluminium atoms
4) these then sink to the bottom of the electrolysis tank
5) the negative O2- ions are attracted to the positive electrode where they each lose two electrons. the neutral oxygen atoms will then combine to form O2 molecules
96
give the two half equations for the aluminium oxide electrolysis example
Al3+ + 3e- > Al
| 2O2 > O2 + 4e-
97
what do you have to factor in when electrolysing an aqueous solution
the ions in the water
98
Electrolysis is very expensive because…
Melting the compounds such as aluminum oxide requires a lot of energy
A lot of energy is required to produce the electric current
99
what ions are in aqueous solutions
H+
| OH-
100
what do you do to work out if chlorine hydrogen or oxygen are made
chloride bleaches litmus paper
hydrogen makes a squeaky pop with lighted splint
oxygen will relight a glowing splint
