C6 Flashcards
(186 cards)
1
Q
Why is it called a redox reaction?
A
Because reduction and oxidation happens at the same time
2
Q
What is reduction?
A
Gain of electrons
3
Q
What is oxidation?
A
Loss of electrons
4
Q
What is an oxidising agent?
A
One that accepts electrons and gets reduced
5
Q
What is a reducing agent?
A
It donates electrons and gets oxidised
6
Q
Give an example of a redox reaction
A
Iron atoms are oxidised to iron(11) ions when they react with dilute acid
Iron atoms lose electrons - they’re oxidised by the hydrogen ions
Hydrogen ions gain atoms they are reduced by the iron atoms
7
Q
What are displacement reactions?
A
Redox reactions
8
Q
What does a displacement reaction involve?
A
One metal kicking another metal out of a compound (reactive metal into solution of a dissolved metal compound)
9
Q
What is the rule for a displacement reaction?
A
A more reactive metal will displace (and replace) a less reactive metal from its compound
10
Q
Describe a displacement reaction
A
It’s always the metal ions that gain electrons and get reduced
The metal atom always loses electrons and is oxidised
11
Q
What is the rusting of iron?
A
A redox reaction
12
Q
When does rusting happen?
A
When the irons in contact with both oxygen and water
13
Q
What is rust?
A
Hydrated iron (111) oxide
14
Q
What is the word equation for rusting of iron?
A
Iron + oxygen + water = hydrated iron
(111) oxide
15
Q
What happens in the rusting of iron?
A
Iron loses electrons when it reacts with oxygen (each iron atom loses three electrons) - oxidised
Oxygen gains electrons when it reacts with iron (each oxygen atom gains two electrons) - reduced
16
Q
Describe metals being combined with other things to prevent rust
A
Iron can be mixed with other metals to prevent rust (alloy)
Eg Steels are alloys of iron and Carbon
- stainless steel is iron Carbon and chromium - it’s rustproof
17
Q
Give some examples of preventing rusting by coating the iron with a barrier
A
Keeps out water, oxygen or both
Painting - ideal for large and small structures
Oiling or greasing is used when moving parts are involved (bike chains)
18
Q
Describe a tin coating preventing rusting
A
tin plated
Tin acts as barrier stopping oxygen and water from reaching the surface of the iron
Only works if the tin remains intact (not scratched)
If tin scratched iron will lose electrons in preference to tin (because tin is less reactive than iron) and it will rust even faster than if it was on its own
19
Q
What is the sacrificial method?
A
Placing a more reactive metal with the iron to prevent rusting - water and oxygen react with this and not the iron
20
Q
Give two examples of the sacrificial method
A
Galvanising - coat of zinc - zinc is more reactive so loses electrons in preference to iron and acts as a barrier
Blocks of metal (magnesium) bolted to iron - used on hulls of ships or underground iron pipes
21
Q
What does electrolysis mean?
A
Splitting up with electricity
22
Q
Describe electrolysis
A
Electric current passed through a molten or dissolved ionic compound causing it to decompose
Creates flow of charge through electrolyte
As ions gain or lose electrons at cathode or anode they become atoms or molecules and are discharged from the solution
23
Q
What happens at the cathode in electrolysis?
A
Positive ions move towards cathode and gain electrons
24
Q
What happens at the anode in electrolysis?
A
Negative ions move towards anode and lose electrons
25
What can happen in the electrolysis of aqueous solutions?
Aqueous solutions contain ions from the water as well as ions from the solute (ionic compound)
Sometimes it's easier to discharge the ions from the water instead of the ones from the solute depending on how easily the ions lose or gain electrons
26
What is produced at the anode and cathode in the electrolysis of aqueous sulfuric acid?
Hydrogen gas at cathodes
| Oxygen at anode
27
What is produced at the anode and cathode during the electrolysis of Aquila sodium hydroxide solution?
Cathode - hydrogen gas
| Anode- oxygen
28
What can copper (11) sulphate be electrolysed to form?
Copper and oxygen
29
What happens in the electrolysis of copper (11) sulfate solution when you use Carbon dioxide?
The cathode starts off as a piece of carbon but gets coated with a layer of copper (because copper ions are easier to discharge than hydrogen ions) - reduced
At the anode the hydroxide ions are discharged and converted into oxygen and water - oxidised
30
Which is the negative electrode?
Cathode
31
Which is the positive electrode?
Anode
32
What is the ionic equation for the reaction at the cathode in the electrolysis of copper (11) sulfate solution?
Cu2+ + 2e- -> Cu
33
What is the ionic equation for the reaction at the anode during the electrolysis of copper (11) sulfate solution?
4OH- - 4e- -> O2 + 2H2O
34
What happens in the electrolysis of molten ionic compounds?
Broke up into their elements
Positive metal ions are reduced to atoms at the cathode
Negative ions are oxidised to atoms at the anode
35
Why can molten ionic compounds be electrolysed?
Because the ions can move more freely
36
What is the solution that you electrolysed called?
Electrolyte
37
How do you increase the number of electrons transferred in electrolysis?
Electrolysing for a longer time
| Increasing the current
38
What does increasing the amount of electrons transferred mean in electrolysis?
More product is produced
39
What is the amount of product produced in electrolysis proportional to?
Directly proportional to the time taken and current used
40
What is the amount of charge (Q- coulombs) flowing through a circuit in electrolysis equal to?
Current (I) multiplied by time (s)
| Q=It
41
What equation can you use to work out the amount of product formed in electrolysis?
Q=It
42
When is it a redox reaction?
If electrons are transferred
43
What do fuel cells use to make electricity?
Hydrogen and oxygen
44
What do hydrogen and oxygen do when they react?
Give out energy
45
What kind of reaction is the one between hydrogen and oxygen?
Exothermic - releases energy
46
What does it mean when a reactions exothermic?
Less energy is taken to break bonds than is released in making bonds
47
What is a fuel cell?
An electrical cell that's supplied with a fuel and oxygen ad uses energy from the reaction between them to produce electrical energy efficiently
48
What does hydrogen-oxygen fuel cell do?
Combines hydrogen and oxygen to release heat energy and water - no nasty pollutants
49
What reaction do hydrogen-oxygen fuel cells involve?
A redox reaction
50
What electrolyte is used in a hydrogen-oxygen fuel cell?
Potassium hydroxide
51
What electrodes are used in a hydrogen-oxygen fuel cell?
Porous Carbon with a catalyst
52
What happens at the cathode in a hydrogen-oxygen fuel cell?
Oxygen gains electrons (reduction) and reacts with water to make OH-
O2 + 4e- + H2O -> 4OH-
53
What happens at the anode in a hydrogen-oxygen fuel cell?
Hydrogen (loses electrons - oxidation) combines with hydroxide ions to produce water and electrons
2H2 + 4OH- -> 4H2O + 4e-
54
How does a hydrogen-oxygen fuel cell make electricity?
The electrons released by the hydrogen gas at the anode flow through an external circuit from the anode to the cathode (to react with oxygen) creating the electric current
55
What is the overall reactions equation in a hydrogen-oxygen fuel cell?
Hydrogen + oxygen -> water
| 2H2 + O2 -> 2H2O
56
What are the advantages of hydrogen-oxygen fuel cells?
Much more efficient than power stations or batteries (efficiency can be 80%)
Electricity generated directly from the reaction (direct energy transfer) so no turbines or generators
Aren't a lot of stages so fewer places for energy to be lost
No moving parts so energy isn't lost as friction
Only product is water - no pollution
57
What are the disadvantage s of hydrogen-oxygen fuel cells?
Producing hydrogen needed requires a lot of energy - may have come from burning fossil fuels - pollution
Often contain poisonous catalysts which eventually have to be disposed of - takes time and money and can cause environmental problems
58
Where are hydrogen-oxygen fuel cells used?
To provide electrical power in spacecraft
59
Why are hydrogen-oxygen fuel cells used in space craft?
```
Hydrogen and oxygen readily available from the rocket fuel tanks
Lightweight and compact
No moving parts that could go wrong
The product is used as drinking water
No other waste products to get rid of
```
60
Why is the car industry developing fuel cells?
Replace conventional petrol/Diesel engines
Fuel cells don't produce pollution - good for cities with air pollution issues
Hydrogen can be obtained from decomposing water so large amount available
61
What are CFCs?
Chlorofluorocarbons
| Organic molecules containing Carbon, chlorine and fluorine
62
What are the advantages of CFCs?
```
Non-toxic
Non-flammable
Chemically inert
Insoluble in water
Low boiling points
-ideal for many uses
```
63
What were CFCs used in?
Coolants in refrigerators and air conditioning systems
| Propellants in aerosols
64
When did scientists discover that chlorine helps destroy ozone?
1974
65
When did scientists find evidence of decreasing ozone levels over Antarctica?
1985
66
What supports the hypothesis that CFCs destroy ozone?
High levels of compounds produced by the breakdown of CFCs in the upper atmosphere
67
What is ozone?
A form of oxygen (O3 - three oxygen atoms) that is in the stratosphere in the ozone layer
68
What does ozone do?
Absorbs ultraviolet light from the sun
Absorbs UV light and breaks down into oxygen molecule and an oxygen atom
O3 + UV -> O + O2
Oxygen molecule and oxygen atom join to make ozone again
O + O2 -> O3
Natural balance
69
What does reducing the amount of ozone in the stratosphere cause?
More UV light hitting the surface of the earth
| Increased risk of sunburn and skin cancer
70
Which countries banned CFCs as aerosol propellants in 1978?
USA
Canada
Sweden
Norway
71
What happened after the ozone hole was discovered?
Many countries got together and decided to reduce CFC production and eventually ban them altogether
72
How are free radicals made?
By breaking covalent bonds evenly so each atom gets one of the shared electrons making the free radical very, very reactive because of the unpaired electron (unpaired electron showed by dot •)
73
What does UV light do to the Carbon-chlorine bonds in CFCs?
Break to form free radicals
| Only happens in the stratosphere where UV light is stronger
74
What is the equation for the breaking up of CFCs?
CCl2F2 -> CClF2• + Cl•
75
Why are the chlorine free radicals dangerous?
React with ozone turning into ordinary oxygen and chlorine oxide (free radical) which then reacts with more ozone to make two oxygen molecules and another Cl• free radical
Chain reaction so just one chlorine free radical can break up lots of ozone
Chlorine atoms aren't used up so just carry on
76
What are the equations for the chlorine free radicals destruction?
O3 + Cl• -> ClO• + O2
| ClO• + O3 -> 2O2 + Cl•
77
Why do CFCs stay in the stratosphere for ages?
Not very reactive so only react with one or two chemicals in the atmosphere and will only break up in the stratosphere
78
What are safe alternatives to CFCs?
Alkanes and Hydrofluorocarbons (HFCs)
79
How can you tell if it's hard water?
It makes a scum with soap
| It forms limescale
80
Why is limescale bad in your kettle?
It's a thermal insulator so it will take longer to boil
| (also can eventually block pipes)
81
What is hard water caused by?
Calcium ions and magnesium ions
| As water flows of rocks containing calcium and magnesium compounds these dissolve in it
82
What is the only way calcium carbonate gets into water?
Calcium carbonate is insoluble but will react with acids and rainwater is slightly acidic because of the CO2 from the air dissolved in it so it reacts to form calcium hydrogencarbonate
83
What is the equation for rainwater reacting with calcium carbonate?
Carbon dioxide + water + calcium carbonate -> calcium hydrogencarbonate
84
What do fuel cells use to make electricity?
Hydrogen and oxygen
85
What do hydrogen and oxygen do when they react?
Give out energy
86
What kind of reaction is the one between hydrogen and oxygen?
Exothermic - releases energy
87
What does it mean when a reactions exothermic?
Less energy is taken to break bonds than is released in making bonds
88
What is a fuel cell?
An electrical cell that's supplied with a fuel and oxygen ad uses energy from the reaction between them to produce electrical energy efficiently
89
What does hydrogen-oxygen fuel cell do?
Combines hydrogen and oxygen to release heat energy and water - no nasty pollutants
90
What reaction do hydrogen-oxygen fuel cells involve?
A redox reaction
91
What electrolyte is used in a hydrogen-oxygen fuel cell?
Potassium hydroxide
92
What electrodes are used in a hydrogen-oxygen fuel cell?
Porous Carbon with a catalyst
93
What happens at the cathode in a hydrogen-oxygen fuel cell?
Oxygen gains electrons (reduction) and reacts with water to make OH-
O2 + 4e- + H2O -> 4OH-
94
What happens at the anode in a hydrogen-oxygen fuel cell?
Hydrogen (loses electrons - oxidation) combines with hydroxide ions to produce water and electrons
2H2 + 4OH- -> 4H2O + 4e-
95
How does a hydrogen-oxygen fuel cell make electricity?
The electrons released by the hydrogen gas at the anode flow through an external circuit from the anode to the cathode (to react with oxygen) creating the electric current
96
What is the overall reactions equation in a hydrogen-oxygen fuel cell?
Hydrogen + oxygen -> water
| 2H2 + O2 -> 2H2O
97
What are the advantages of hydrogen-oxygen fuel cells?
Much more efficient than power stations or batteries (efficiency can be 80%)
Electricity generated directly from the reaction (direct energy transfer) so no turbines or generators
Aren't a lot of stages so fewer places for energy to be lost
No moving parts so energy isn't lost as friction
Only product is water - no pollution
98
What are the disadvantage s of hydrogen-oxygen fuel cells?
Producing hydrogen needed requires a lot of energy - may have come from burning fossil fuels - pollution
Often contain poisonous catalysts which eventually have to be disposed of - takes time and money and can cause environmental problems
99
Where are hydrogen-oxygen fuel cells used?
To provide electrical power in spacecraft
100
Why are hydrogen-oxygen fuel cells used in space craft?
```
Hydrogen and oxygen readily available from the rocket fuel tanks
Lightweight and compact
No moving parts that could go wrong
The product is used as drinking water
No other waste products to get rid of
```
101
Why is the car industry developing fuel cells?
Replace conventional petrol/Diesel engines
Fuel cells don't produce pollution - good for cities with air pollution issues
Hydrogen can be obtained from decomposing water so large amount available
102
What are CFCs?
Chlorofluorocarbons
| Organic molecules containing Carbon, chlorine and fluorine
103
What are the advantages of CFCs?
```
Non-toxic
Non-flammable
Chemically inert
Insoluble in water
Low boiling points
-ideal for many uses
```
104
What were CFCs used in?
Coolants in refrigerators and air conditioning systems
| Propellants in aerosols
105
When did scientists discover that chlorine helps destroy ozone?
1974
106
When did scientists find evidence of decreasing ozone levels over Antarctica?
1985
107
What supports the hypothesis that CFCs destroy ozone?
High levels of compounds produced by the breakdown of CFCs in the upper atmosphere
108
What is ozone?
A form of oxygen (O3 - three oxygen atoms) that is in the stratosphere in the ozone layer
109
What does ozone do?
Absorbs ultraviolet light from the sun
Absorbs UV light and breaks down into oxygen molecule and an oxygen atom
O3 + UV -> O + O2
Oxygen molecule and oxygen atom join to make ozone again
O + O2 -> O3
Natural balance
110
What does reducing the amount of ozone in the stratosphere cause?
More UV light hitting the surface of the earth
| Increased risk of sunburn and skin cancer
111
Which countries banned CFCs as aerosol propellants in 1978?
USA
Canada
Sweden
Norway
112
What happened after the ozone hole was discovered?
Many countries got together and decided to reduce CFC production and eventually ban them altogether
113
How are free radicals made?
By breaking covalent bonds evenly so each atom gets one of the shared electrons making the free radical very, very reactive because of the unpaired electron (unpaired electron showed by dot •)
114
What does UV light do to the Carbon-chlorine bonds in CFCs?
Break to form free radicals
| Only happens in the stratosphere where UV light is stronger
115
What is the equation for the breaking up of CFCs?
CCl2F2 -> CClF2• + Cl•
116
Why are the chlorine free radicals dangerous?
React with ozone turning into ordinary oxygen and chlorine oxide (free radical) which then reacts with more ozone to make two oxygen molecules and another Cl• free radical
Chain reaction so just one chlorine free radical can break up lots of ozone
Chlorine atoms aren't used up so just carry on
117
What are the equations for the chlorine free radicals destruction?
O3 + Cl• -> ClO• + O2
| ClO• + O3 -> 2O2 + Cl•
118
Why do CFCs stay in the stratosphere for ages?
Not very reactive so only react with one or two chemicals in the atmosphere and will only break up in the stratosphere
119
What are safe alternatives to CFCs?
Alkanes and Hydrofluorocarbons (HFCs)
120
How can you tell if it's hard water?
It makes a scum with soap
| It forms limescale
121
Why is limescale bad in your kettle?
It's a thermal insulator so it will take longer to boil
| (also can eventually block pipes)
122
What is hard water caused by?
Calcium ions and magnesium ions
| As water flows of rocks containing calcium and magnesium compounds these dissolve in it
123
What is the only way calcium carbonate gets into water?
Calcium carbonate is insoluble but will react with acids and rainwater is slightly acidic because of the CO2 from the air dissolved in it so it reacts to form calcium hydrogencarbonate
124
What is the equation for rainwater reacting with calcium carbonate?
Carbon dioxide + water + calcium carbonate -> calcium hydrogencarbonate
125
What are the two kinds of hardness?
Temporary hardness
| Permanent hardness
126
What is temporary hardness caused by?
The hydrogencarbonate ion
127
What is permanent hardness caused by?
Dissolved calcium sulfate
128
How is temporary hardness removed?
By boiling
| The calcium hydrogencarbonate decides to form insoluble calcium carbonate
129
What is the equation for boiling temporary hardness water?
Calcium hydrogencarbonate
->
Calcium carbonate + water + carbon dioxide
Ca(HCO3)2 -> CaCO3 + H2O + CO2
130
How can both types of hardness be removed?
Adding washing soda (sodium carbonate) - carbonate ions join to calcium ions making an insoluble precipitate of calcium carbonate
Ion exchange resin - lots of sodium or hydrogen ions are exchanged for calcium or magnesium ions
131
What is the equation for removing hardness by adding washing soda?
Ca2+ + CO32- -> CaCO3
132
Describe an experiment that compares the hardness of water samples
Add 100cm3 of water to conical flask
Add 1cm3 soap solution
Put a bung in and shake
Keep adding soap until a good lasting lather has formed (bubbles cover surface for at least 30 seconds)
Record how much soap needed
Then repeat this time boiling the water first to see of hardness is temporary or not
133
What is the general formula of an alcohol?
C(n)H(2n+1)OH
134
What makes ethanol?
Fermentation
135
What is the word equation for fermentation?
Glucose -> ethanol + Carbon dioxide
136
What is the symbol equation for fermentation?
C6H12O6 -> 2C2H5OH + 2CO2
137
How is fermentation used?
To convert sugars into ethanol - the reaction is caused by enzymes found in yeast
138
What conditions are needed for fermentation?
Temperature carefully controlled to prevent denaturing and inactive-ness (too cold) - carried out at optimum - between 25 and 50 degrees
Prevent oxygen from interfering as this will convert ethanol into ethanoic acid
139
How is pure ethanol got from the products of fermentation?
Fractional distillation
140
How is ethanol made industrially?
By hydrating ethene
141
Describe the industrial process for making ethanol
Ethene reacts with steam to make ethanol
Needs 300 degrees C and pressure of 70 atmospheres
Reaction sped up by being passed over a heated phosphoric acid catalyst
142
What is the word equation for the hydration of ethene?
Ethene + water (steam) -> ethanol
143
What is the symbol equation for the hydration of ethene?
C2H4 + H2O -> C2H5OH
144
Compare the two ways of manufacturing ethanol
Fermentation is a batch process - slow and inefficient
Ethene hydration is a continuous process - ethanol made quicker but is more expensive to run because requires harsher conditions
145
Compare the two ways of making ethanol by sustainability
Ethanol made by fermentation is a renewable fuel made from renewable sources
Hydration is non renewable made from crude oil
146
Compare the two ways of making ethanol by purity
Ethanol by fermentation isn't very pure and has to be distilled
Hydration has a higher purity
147
Compare the two ways of making ethanol by atom economy
Fermentation has a lower atom economy than hydration
148
Compare the two ways of making ethanol by percentage yield
Yield of hydration is low but by recycling unused products it has a 95% yield
Yields achieved by fermentation are much lower
149
Where do fats and oils come from?
Annals or plants
150
Give some examples of animal fats and oils
Lard (pork fat)
Blubber (whale fat)
Ghee (butter oil)
Cod liver oil
151
Give some examples of plants fats and oils
Walnut oil
Coconut oil
Olive oil
Soya oil
152
What happens to fats and oils at room temperature?
Fats are solid
| Oils are liquid
153
What are fats and oils?
Esters (what you get when you react an acid with an alcohol)
154
How are fats and oils produced?
When an alcohol (glycerol) reacts with fatty acids
155
Why are natural fats and oils important raw materials for the chemical industries?
Can be used as alternatives to chemicals made from crude oil
Used in
Paints, machine lubricants, detergents and cosmetics
156
What are emulsions made from?
Oil and water
| Have to be shaken vigorously to mix so the oil is broken into small drops which diapers throughout the water
157
What does immiscible mean?
Doesn't mix in water
158
Which out of oils and fats is immiscible?
Oils
159
What is an oil in water emulsion?
Oil droplets suspended in water
| Eg milk
160
What is a water in oil suspension?
Water droplets suspended in oil
| Eg butter
161
What can vegetable oils be used to make?
Biodiesel
| Oils such as rapeseed and soybean can be processed and turned into fuels because they provide a lot of energy
162
What are fats and oils used to make?
Soaps
163
How do fats and oils make soap?
Vegetable oils react with alkali to make soap
Natural fats and oils are boiled with sodium hydroxide - the hot sodium hydroxide splits them up to produce soap and glycerol - saponification
164
Describe saponification
Fat or oil broken up to release glycerol and fatty acids - hydrolysis
Then fatty acids react with the sodium hydroxide to make soap
165
What is the word equation for making soap?
Fat + sodium hydroxide -> soap +
| Glycerol
166
What do fats and oils contain?
Long chain molecules with lots f Carbon atoms
167
What can fats and oils be?
Saturated or unsaturated
168
What are monounsaturated fats?
Ones which contain one double bond somewhere in their Carbon chains
169
What are polyunsaturated fats?
Ones which contain more than one double bond
170
How do detect whether it's saturated or unsaturated
Bromine water test
Saturated and the bromine water stays orange
Unsaturated and and addition reaction will take place making a colourless dibromo compound and the bromine water is decolourised
171
What can unsaturated oils be?
Hydrogented
172
Describe hydrogenation
Hardening unsaturated oils by reacting them with hydrogen in the presence of a nickel catalyst at 60 degrees
- hydrogen reacts with the double bond
173
How is margarine made?
Partially hydrogenating unsaturated vegetable oil - so it's easy to spread (hydrogenating all and it would be too hard)
174
Why are saturated fats less healthy than unsaturated fats?
Saturated fats increase the amount of cholesterol in the blood - increasing risk of heart disease
175
What do natural unsaturated oils do?
Reduce the amount of blood cholesterol
176
What do vegetable fats and oils tend to be?
Unsaturated
177
What do animal fats and oils tend to be?
Saturated
178
What does partially hydrogenated vegetable oil do?
Increase amount of bad cholesterol and decrease amount of food cholesterol - increase risk of heart disease
179
What do detergents and soaps have?
A hydrophobic tail and a hydrophilic head
180
What is the hydrophobic tail of a detergent molecule usually?
A long hydrocarbon chain
181
What is the hydrophilic head of a detergent molecule usually?
Small and ionic
182
How do detergents remove oil?
Hydrophobic tail forms string intermolecular forces with fats and oils and hydrophilic head with water molecules so surround the fat and oil droplets on clothes and lift them out of the fabric
183
What is dry cleaning?
Any cleaning process that uses other solvents instead of water
184
Why are solvents better at removing oil and grease than detergents?
They completely dissolve them
Weak intermolecular forces between solvent molecules and between grease molecules
Grease molecules are surrounded by solvent because intermolecular forces formed between them so when solvent removed the grease is removed as well
185
What do biological detergents contain?
Biological catalysts that help break down large insoluble molecules into small soluble molecules
186
Why are biological detergents good?
Wash at lower temperatures so not denatured enzymes - saves money
(40 degrees C)
Can wash more delicate clothes in washing machine because washing at a cooler temperature
