Electrochemistry Flashcards
(107 cards)
1
Q
How do you measure reactivity?
A
by how easily elements lose electrons or are oxidised
2
Q
Electrode Potential Definition
A
the electrode potential of a metal is a measurement of the tendency of a metal to lose electrons i.e the ability to be oxidised
3
Q
how would you measure Electrode Potential
A
using a voltaic cell
4
Q
what does a voltaic cell do?
A
a voltaic cell uses a spontaneous chemical reaction to generate electric current
5
Q
if 2 different metals e.g. copper and zinc are immersed in an electrolyte e.g. a dissolved sulfate salt, what happens?
A
one metal is oxidised and one metal is reduced
6
Q
electrolyte
A
a substance that can conduct electricity easily, in the molten or dissolved state, usually a salt or an ionic compound
7
Q
oxidation of zinc (2)
A
Zn - 2e- -> Zn2+
8
Q
reduction of copper ions (2)
A
Cu+2 +2e- -> Cu
9
Q
what provides the electric power for the voltaic cell?
A
the difference in the oxidation potential of the two metals provides the electric power of cell, registered on the voltmeter
10
Q
if one metal was replaced with another in a voltaic cell
A
a different voltage would be observed
11
Q
if zinc was replaced with lead
A
the voltage would be less as lead has less of a tendency to lose electrons than zinc
12
Q
if zinc was replaced with magnesium
A
the voltage would be higher as magnesium has a greater tendency to lose electrons than zinc
13
Q
reference cell for chemists for measuring all electrode potentials
A
hydrogen half cell
14
Q
hydrogen half cell
A
consists of a platinum electrode (inert) immersed in a solution of H+ ions, with hydrogen gas bubbled over the electrode
15
Q
electrochemical series
A
a list of metals in order of their ability to lose electrons or be oxidised
16
Q
metals at the top of the electrochemical series ( Electrode Potential)
A
highly electropositive
17
Q
metals at the bottom of the electrochemical series (Electrode Potential)
A
less electropositive
18
Q
metals at the top of the electrochemical series (reactivity)
A
extremely reactive
19
Q
metals at the bottom of the electrochemical series (reactivity)
A
less reactive
20
Q
metals at the top of the electrochemical series (stability)
A
form very stable compounds
21
Q
metals at the bottom of the electrochemical series (stability)
A
form less stable compounds
22
Q
metals at the top of the electrochemical series (nature)
A
not free in nature (very reactive)
23
Q
metals at the bottom of the electrochemical series (nature)
A
can be found free in nature
24
Q
one last thing about metals at the top of the electrochemical series
A
they will displace those lower down from a solution of their salts
25
Acronym to remember the electrochemical series
little polly can seldom marry a zulu in the lovely honolulu causing many strange glances
26
little
lithium
27
polly
potassium
28
can
calcium
29
seldom
sodium
30
marry
magnesium
31
a
aluminium
32
zulu
zinc
33
in
iron
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the
tin
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lovely
lead
36
honolulu
hydrogen
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causing
copper
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many
mercury
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strange
silver
40
glances
gold
41
reaction between sodium and zinc chloride
| metals higher up in Ec.s displace those lower down
2Na + ZnCl2 -> Zn + 2 NaCl
42
equation for scrap iron used to extract copper metal from a solution of its salts
Fe + Cu2+ -> Cu(↓) + Fe+2
43
EXPERIMENT - DISPLACEMENT REACTIONS OF METALS
| Zinc in copper (II) sulfate solution
some pieces of zinc metal added to solution of copper sulfate
copper (reddish) metal appears on the zinc and some of the zinc dissolves
colour of copper sulfate becomes less blue
44
EXPERIMENT - DISPLACEMENT REACTIONS OF METALS
| magnesium in copper (II) sulfate solution
some pieces of magnesium were added to a solution of copper (II) sulfate
copper (reddish) appears in magnesium and some of the magnesium dissolves
solution becomes less blue in colour
45
OXIDATION OF SULPHITE TO SULPHATE USING A HALOGEN SUCH AS CHLORINE WATER (OR BROMINE OR IODINE)
some sodium sulphite added to test tube
some chlorine water wad then added
the solution was tested for the presence of sulphate ions by added barium chloride to form a white precipitate that is insoluble by HCl
46
halogens oxidise iron (II) to
iron (III)
47
halogens are
oxidising agents
48
of chlorine, bromine and iodine, which is the strongest oxidising agent?
chlorine
49
COMPARING HALOGENS AS OXIDISING AGENTS
| first step
chlorine water added to a bromide salt
50
COMPARING HALOGENS AS OXIDISING AGENTS
| result of first step
the solution turns a red/orange colour as bromine is formed
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COMPARING HALOGENS AS OXIDISING AGENTS
| second step
chlorine water added to an iodide salt
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COMPARING HALOGENS AS OXIDISING AGENTS
| result of seconds step
solution turns a red/brown as iodine is formed
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COMPARING HALOGENS AS OXIDISING AGENTS
| third step
bromine water is added to an iodide salt
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COMPARING HALOGENS AS OXIDISING AGENTS
| result of third step
solution turns a red/brown as iodine is formed
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COMPARING HALOGENS AS OXIDISING AGENTS
| fourth step
bromine water added to chloride salt
56
COMPARING HALOGENS AS OXIDISING AGENTS
| result of fourth step
no reaction occurs, as chlorine is a stronger oxidising agent
57
electrolysis definition
a process where an electrical current is used to bring about a chemical reaction
58
electrolysis: what splits up the chemical substances
electricity
59
electrolysis: what carries the current and why
an electrolyte - contains ions that are free to move
60
electrolysis: how to connect to power supply
electrodes- inert (platinum or graphite) or metal itself
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electrolysis: where does reduction take place
cathode (-)
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electrolysis: where does oxidation take place
anode (+)
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electrolysis: as soon as current begins to flow
chemical changes occur
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1. ELECTROLYSIS OF ACIDIFIED WATER USING INTERT ELECTRODES
| compounds involved
H2O and H2SO4
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1. ELECTROLYSIS OF ACIDIFIED WATER USING INTERT ELECTRODES
| cathode, reduction equation
4H2O + 4e- -> 2H2 + 4OH-
66
1. ELECTROLYSIS OF ACIDIFIED WATER USING INTERT ELECTRODES
| anode, oxidation equation
2H2O - 4e- -> O2 + 4H+
67
1. ELECTROLYSIS OF ACIDIFIED WATER USING INTERT ELECTRODES
| cathode explanation
reduction, water molecules gain electrons, to form hydrogen gas. To test for hydrogen gas the gas is collected in a test tube and you hear a pop when lighting
68
1. ELECTROLYSIS OF ACIDIFIED WATER USING INTERT ELECTRODES
| anode explanation
oxidation, electrons are lost from the water molecules which causes the water molecules to break down and oxygen gas is produced, to test for oxygen gas, the gas is collected in a test tube and when a glowing splint is inserted into a test tube, it relights
69
1. ELECTROLYSIS OF ACIDIFIED WATER USING INTERT ELECTRODES
| overall reaction
2H2O -> 2H2 + O2
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1. ELECTROLYSIS OF ACIDIFIED WATER USING INTERT ELECTRODES
| ratio of H2 to O2
2:1
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1. ELECTROLYSIS OF ACIDIFIED WATER USING INTERT ELECTRODES
| electrolyte
sulfuric acid, doesn't take part however as it is very low done in the series - not easily oxidised
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1. ELECTROLYSIS OF ACIDIFIED WATER USING INTERT ELECTRODES
| where is it carried out
in a Hoffman voltmeter
73
2.ELECTROLYSIS OF AQUEOUS SODIUM SULPHATE USING INERT ELECTRODES AND UNIVERSAL INDICATOR
compounds involved
H2O and Na2SO4
74
2.ELECTROLYSIS OF AQUEOUS SODIUM SULPHATE USING INERT ELECTRODES AND UNIVERSAL INDICATOR
cathode, reduction equation
4H2O + 4e- -> 2H2 + 4OH-
75
2.ELECTROLYSIS OF AQUEOUS SODIUM SULPHATE USING INERT ELECTRODES AND UNIVERSAL INDICATOR
anode, oxidation equation
2H2O - 4e- -> O2 + 4H+
76
2.ELECTROLYSIS OF AQUEOUS SODIUM SULPHATE USING INERT ELECTRODES AND UNIVERSAL INDICATOR
cathode explanation
reduction, water molecules gain electrons and hydrogen gas produced, production of hydroxide ions, area around cathode becomes alkaline - blue in universal indicator
77
2.ELECTROLYSIS OF AQUEOUS SODIUM SULPHATE USING INERT ELECTRODES AND UNIVERSAL INDICATOR
anode explanation
oxidation, water molecules lose electrons and oxygen gas is liberated, production of hydrogen ions at anode. area around anode becomes acidic - red in universal indicator
78
universal indicator in neutral solution
green
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3. ELECTROLYSIS OF AQUEOUS POTASSIUM IODIDE USING INERT ELECTRODES AND PHENOLPHTHALEIN INDICATOR
compounds involved
H2O and KI
80
3. ELECTROLYSIS OF AQUEOUS POTASSIUM IODIDE USING INERT ELECTRODES AND PHENOLPHTHALEIN INDICATOR
cathode reduction equation
2H2O + 2e- -> H2 + 2OH-
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3. ELECTROLYSIS OF AQUEOUS POTASSIUM IODIDE USING INERT ELECTRODES AND PHENOLPHTHALEIN INDICATOR
anode oxidation equation
2I- -2e- -> I2
82
3. ELECTROLYSIS OF AQUEOUS POTASSIUM IODIDE USING INERT ELECTRODES AND PHENOLPHTHALEIN INDICATOR
cathode explanation
reductio, water molecules gain electrons and hydrogen gas liberated. Build up of hydroxide ions, area around cathode alkaline, phenolphthalein indicator pink in alkaline soln, pink around cathode
83
3. ELECTROLYSIS OF AQUEOUS POTASSIUM IODIDE USING INERT ELECTRODES AND PHENOLPHTHALEIN INDICATOR
anode explanation
oxidation, iodide ions are oxidised and lose electrons to form iodine as iodine is relatively high in electrochemical series, easily oxidised, red brown colour observed from I2
84
electrodes for experiments 1,2 and 3
inert
85
4. ELECTROLYSIS OF AQUEOUS COPPER (II) SULPHATE USING COPPER ELECTRODES
compounds involved
H2O and CuSO4 and Cu (electrodes)
86
4. ELECTROLYSIS OF AQUEOUS COPPER (II) SULPHATE USING COPPER ELECTRODES
cathode, reduction equation
Cu2+ + 2e- -> Cu
87
4. ELECTROLYSIS OF AQUEOUS COPPER (II) SULPHATE USING COPPER ELECTRODES
anode, oxidation equation
Cu - 2e- -> Cu 2+
88
4. ELECTROLYSIS OF AQUEOUS COPPER (II) SULPHATE USING COPPER ELECTRODES
cathode explanation
copper (II) ions from copper (II) sulphate soln. are attracted to cathode, as copper is relatively high in the electrochemical series. Reduction occurs, so the ions gain electrons to form copper metal. An increase in weight of the cathode as more copper is being deposited
89
4. ELECTROLYSIS OF AQUEOUS COPPER (II) SULPHATE USING COPPER ELECTRODES
anode explanation
the copper from anode is oxidised and loses electrons to become copper (II) ions, replaces copper (II) ions lost at cathode. decrease in weight at anode as the copper is being oxidised (corroded away)
90
why does copper need to be purified for industry?
as impurities present naturally in copper reduce its ability to conduct electricity
91
PURIFICATION OF COPPER
| anode
made of impure copper, oxidation occurs here and the copper in the impure anode loses electrons to become copper (II) ions
92
PURIFICATION OF COPPER
| cathode
made of a thin sheet of pure copper, reduction occurs here and the copper (II) ions of the electrolyte (Copper (II) sulphate) gain electrons to form copper metal
the copper metal is pure and is deposited on the cathode
93
PURIFICATION OF COPPER
| what happens to the impurities
they fall to the bottom of the apparatus
| these are valuable as the contain gold
94
covering a nickel spoon with silver:
| spoon is the
cathode
95
covering a nickel spoon with silver:
| silver is the
anode
96
covering a nickel spoon with silver:
| electrolyte
a silver salt
97
covering a nickel spoon with silver:
| anode equation
Ag - e- -> Ag+
98
covering a nickel spoon with silver:
| cathode equation
Ag+ +e- -> Ag
99
covering a nickel spoon with silver:
| quantity of silver deposited depends on 2
time you leave it their
| quantity of electricity passed through electrolyte
100
EPNS
electroplated nickel silver
101
the object to be covered is always the
cathode
102
handlebars o bicycles
plated with chromium to prevent corrosion from rain
103
DEMONSTRATION OF IONIC MOVEMENT
| highly coloured compound
copper chromate
| CuCrO4
104
DEMONSTRATION OF IONIC MOVEMENT
| Cu2+ colour
blue
105
DEMONSTRATION OF IONIC MOVEMENT
| CrO4 2- colour
orange due to chromium with valency +6
106
DEMONSTRATION OF IONIC MOVEMENT
| set up experiment
soak a piece of filter paper with some salt solution, so that it can conduct electricity, and then place some copper chromate crystals on the filter paper and connect it to an electric supply
107
DEMONSTRATION OF IONIC MOVEMENT
| observation
blue Cu2+ ions will be attracted to cathode and orange CrO4 2- ions will be attracted to the anode - demonstrating ionic movement
