ppe pt3 + GCSES (mar/may) Flashcards
chromatography practical needs to be explained
1
Q
What is an element?
A
A substance containing only one type of atom.
2
Q
What is a compound?
A
A substance containing two or more different types of atoms that are chemically bonded.
3
Q
What is the conservation of mass?
A
The law which says atoms can neither be created or destroyed in a reaction - equations must be balanced because of this.
4
Q
What can you add to balance an equation?
A
Put numbers in front of substances in the equation. Start with atoms in a compound and end with elements.
5
Q
What is a mixture?
A
Something consisting of different substances not chemically bonded.
6
Q
Explain filtration.
A
Filtration removes large, insoluble particles from a liquid.
- Grab a flask and insert a funnel
- Fold some filter paper and insert it into the funnel
- Pour the solution little by little into the filter paper so it can funnel into the flask
- Filtrate will appear in the flask and residue will appear in the filter paper
7
Q
Explain evaporation.
A
Evaporation leaves behind crystals of a dissolved substance (solute) if heated gently, causing crystallisation.
- Get a tripod and place gauze on it.
- Place a bunsen burner under it and an evaporating basin on the gauze.
- Pour in your solute into the evaporating basin and light the bunsen burner.
- Once you start to see crystals, take it off the heat and leave to rest.
8
Q
Explain distillation.
A
Distillation involves condensing the evaporated solvent and collecting it.
- Heat solution over a heat source
- The gas of the solvent once evaporated travels through a glass pipe which has cool water on either side to condense it once again, before collecting the liquid in a beaker as shown below.
9
Q
Explain fractional distillation.
A
Fractional distillation is the separation of two different liquids that works because of their different boiling points. It works the same as distillation.
10
Q
Explain chromatography.
A
Chromatography causes substances to rise up paper due to capillary action. Lighter particles move further up the paper.
- The starting line is drawn just above the water line in pencil, all measurements are made from it.
- The mobile phase (solvent) moves up the stationary phase (chromatography paper) due to capillary action.
- This pulls the substances in the mixture upwards, with lighter particles being moved further up the stationary phase.
- The starting line is drawn just above the water line in pencil so it won’t move; all measurements made from this.
- The Rf values can then be compared against that of known substances to identify them.
11
Q
How do you calculate Rf value?
A
Rf value = distance substance moved / distance mobile phase moved
12
Q
What are the 3 main states of matter?
A
- Solid - particles are in a regular arrangement (lattice), vibrate at fixed positions and can’t be compressed.
- Liquid - particles are arranged in an irregular arrangement, can move past each other and can’t be compressed.
- Gas - particles are far apart, can move past each other and collide, move quickly and can be compressed
13
Q
What type of change is a state change?
A
A physical change; no new substance is made.
14
Q
What is needed to overcome the forces of attraction between particles?
A
Energy (heat), as to melt/evaporate the forces of attraction.
15
Q
What is an aqueous?
A
A substance in solution (aq).
16
Q
Say the names of the scientists who altered our understanding of the atomic model in order and explain what they changed.
A
- John Dalton popularised the theory that matter is made of indivisible particles
- JJ Thomson created the ‘plum pudding’ model, which suggested the electrons were embedded in a uniform sphere of positive charge; in the middle was a large proton.
- Ernest Rutherford discovered the nucleus was small and + charged
- Neils Bohr deduced that electrons exist in ‘shells’
- James Chadwick determined that the nucleus must contain neutrons as well as protons.
17
Q
How did Ernest Rutherford discover the nucleus was small and + charged?
A
He launched alpha particles at a gold leaf and found most went straight through and very few deflected back.
18
Q
What is the structure of an atom?
A
Nucleus in the middle including neutrons and protons, with 2 electrons (at least - any more will go on a shell with 8 electrons until a new shell is made) surrounding it.
19
Q
What are the relative charges and mass of protons, neutrons and electrons?
A
Protons have a relative charge of +1 and a relative mass of 1.
Neutrons have a relative charge of 0 and a relative mass of 1.
Electrons have a relative charge of -1 and a relative mass of 0.0005.
20
Q
Define atomic number.
A
The number of protons in a nucleus. An atom must also have the same number of electrons.
(bottom number)
21
Q
How are ions made?
A
By an atom having an unequal amount of protons and neutrons. (the protons have changed).
22
Q
Define mass number (relative atomic mass).
A
The number of protons + neutrons in a nucleus.
(top number)
23
Q
How are isotopes identified?
A
By seeing an element be the same as another - except for having a different number of neutrons.
24
Q
How to find average mass?
A
total mass of 100 atoms / 100
25
Explain the development of the periodic table.
- The elements were initially ordered according to atomic 'weight'
- Dmitri Medeleev realised it made more sense to swap/reverse some of the elements order.
- His table had gaps in it, which he predicted would be for elements undiscovered
- He was eventually proven right
26
Where are the metals on the periodic table?
From group 1 and 2, that block in the middle (and down that column) to the diagonal staircase from aluminium down to tennessine.
The block in the middle are the transition metals.
27
Give the properties of the metal elements and transition metal elements.
- Metals always donate electrons to gain an empty outer shell and form positive ions.
- Transition metals also form positive ions and can donate different numbers of electrons. They also form coloured compounds.
28
Give the properties of non-metals.
- Non-metals always accept electrons to gain a full outer shell.
- They can form negative ions or share electrons to do this
29
Why is hydrogen a floating square?
It can do the things, both metals and non-metals can.
30
What are the alkali metals?
Group 1. They all lose/donate their outer electron so their ions are all (1)+. They get MORE reactive down the group as the outer electron is further from the nucleus and so is donated more readily. (The force of attraction is much less).
31
What are the halogens?
Group 7. They accept 1 electron to gain a full outer shell and form 1- ions. They get LESS reactive down the group and the boiling point increases.
32
What are the noble gases?
Group 0. They are very unreactive because they already have an empty outer shell.
33
What is metallic bonding?
This is how metal atoms bond to each other. They form a lattice of ions surrounded by delocalised electrons. As the electrons are free to move, metals are good conductors of electricity and heat.
34
What is ionic bonding?
This is how metals bond to non-metals. Metal atoms donate electrons to non-metals to form ions. The charges of all ions in an ionic compound must add up to ZERO.
35
Explain dot and cross diagrams.
Dot and cross diagrams show the electrons on the outer shells and represent ionic bonding.
| Search up a diagram if anything.
36
State the structure of an ion and some properties of ionic substances.
Ions are arranged in a lattice of repeating units of positive and negative ions, forming a crystal. Ionic compounds are also called salts.
Ionic substances...
- Have high melting/boiling points due to strong electrostatic forces/ionic bonds between them
- Can conduct electricity when molten or in solution (ions are free to move in these states and carry charge)
NOTE: You can also get molecular ions.
37
What are positive and negative ions known as?
Positive ions are known as cations. Negative ions are known as anions.
*You can remember it as cations are purr-sitive*
38
What is covalent bonding and what does it make?
This is how non-metals bond to each other. Atoms share electrons to gain full outer shells. Every covalent bond consists of a pair of shared electrons. A dot and cross diagram can represent these - with a line representing each bond.
- The number of electrons an atom needs = the number of bonds it makes.
They make simple covalent structures.
39
Do simple covalent structures have high or low boiling points, and why?
They have low boiling points due to weak intermolecular forces that need to be overcome.
40
What is giant covalent bonding?
Covalent bonding that results in structure that consists of repeating units of atoms to make what are essentially giant molecules. They've very high melting points as you would have to break the covalent bond.
41
What are the allotropes of carbon and properties?
Allotropes are structures made of the same element but arranged differently.
- Diamond
One of the hardest known substances due to very strong bonds
- Graphite
Had delocalised electrons form weak bonds between layers, can conduct electricity as these electrons can move - layers can slide past each other
- Graphene (a single layer of graphite)
- Fullerenes/nanotubes
Used for electronic composites, medical purposes
42
What are alloys?
Mixtures of metals: different sized atoms disrupt the lattice, so layers can't slide over each other easily - making them strong.
43
How small are nanoparticles?
1-100nm
44
How small are fine particles?
100-2500nm
45
How small are coarse particles, e.g. dust?
>2500nm
46
Why are fullerenes useful?
Due to their high surface to volume ratio, meaning fewer are needed for the purpose it's needed for. Double the length = half the ratio.
47
What is a buckminster fullerene?
A spherical fullerene.
48
How do you find relative formula mass?
Adding all the relative atomic mass on one side of an equation.
49
What does 1 mole equal to (avogadro's constant)?
6.02\*1023
50
How do you calculate moles?
'grams'/'rams' a.k.a. mass(g)/relative atomic/formula mass
51
How would you answer a question about moles? (e.g.: "How many grams of water would be made if *x*g of [a] reacted completely with [b]?)
- find the mass of [a] (in question: *x*) then calculate into moles.
- moles of [a] = moles of [b]
- if there's a big number in front of [b] in the example equation (given in question), multiply moles by the big number
- find the mass of [b] using the calculation rearranged
| essentially: mass -> moles -> moles -> mass
52
What is stoichiometry?
The ratio of moles of one substance to another in a reaction.
53
What is a limiting reactant?
The reactant which is used up in a equation, without using up the other reactant(s).
54
What must happen in a reaction for the reactants to react completely?
There must be the correct number of moles of both reactants in order to react completely.
55
When a substance is dissolved in water, what happens?
It dissociates into its ions - as does the water (into H+ and OH- ions).
56
How can concentration be given, and how is it calculated?
It can be given in g/dm3 or mol/dm3
57
How do you convert from cm3 or ml to dm3
/ 1000
58
How do you calculate concentration?
concentration (mol/dm3) = moles / volume (dm3)
59
What is percentage yield?
The mass of product is made in a reaction in reality compared to the maximum theoretical mass that could be made (using actual masses).
60
What is atom economy?
How much of a desired product can be made in a reaction compared to the total mass of reactants (use relative atomic masses)
61
How do you calculate atom economy?
(RAM of desired product / total RAM of reactants)\*100
62
How much volume does 1 mole of any gas take up?
24dm3
63
What is room temperature and pressure?
20°C, 1atm
64
How do you convert from moles of gas to volume (dm3)?
\* 24
65
Where is carbon on the reactivity series?
Higher than zinc, lower than aluminium.
66
Where is hydrogen on the reactivity series?
Higher than copper, lower than lead.
67
What are the top 3 most reactive substances on the reactivity series?
- potassium
- sodium
- lithium
68
What are the least 3 most reactive substances on the reactivity series?
- silver
- gold
- platinum (least)
69
When does a displacement reaction occur?
When a more reactive metal displaces a less reactive metal from a compound.
70
What do most metals react with acids to make?
Salt and hydrogen.
71
What do metal carbonates react with acids to make?
A salt, carbon dioxide and water.
72
Are group 1 metals more or less reactive than hydrogen?
More reactive; producing hydrogen gas and a metal hydroxide.
73
How is displacement used to obtain metals from their ores?
You can displace metals from their ores with a more reactive, less valuable metal or carbon. This will take place in a blast furnace. (e.g.carbon in, iron out -> iron oxie is 'reduced' to produce iron).
74
What does oxidation and reduction mean in terms of electrons?
OILRIG.
Oxidation is loss, reduction is gain (of electrons).
75
How do you make a half/ionic equation?
By showing what part of the equation actually oxidises/reduces (loses/gains electrons). Including state symbols!
| e.g Na -> Na+ + e-
76
What happens when an acid reacts with an alkali?
A salt and water are produced if reacted completely. This salt is left in solution, meaning that there is now a mixture of dissociated ions.
77
Reacting sulphuric acid with an alkali, what does it produce?
A metal sulphate salt is formed.
## Footnote
The salt is left in solution; with a mixture of dissociated ions. (Na+, Cl-, H+ and OH-
78
When nitric acid is reacted with an alkali, what is produced?
A metal nitrate salt.
## Footnote
The salt is left in solution; with a mixture of dissociated ions. (Na+, Cl-, H+ and OH-
79
How can you get crystals of the dissolved salts?
By gently heating the solution so the water evaporates, leaving only the salt behind.
80
What is pH dependent on?
- The concentration of H+ ions (^ H+ ^ acidic) or OH- ions (^ OH- ^ alkali).
- How strong/weak an acid is. A stronger acid dissociates more completely and will have a lower pH than a weak acid if they have the same concentration.
81
Give 3 examples of strong acids.
- Hydrochloric
- Sulphuric
- Nitric
82
Give 3 examples of weak acids.
- Ethanoic
- Citric
- Carbonic
83
How does universal indicator give you an indication of pH?
By changing colour.
84
Explain titration.
- A burette is used to measure what volume of acid/alkali is needed to neutralise, to allow us to calculate an unknown concentration.
- Measure 50cm3 of alkali of known concentration using a glass pipette put in conical flask with **methyl orange indicator**.
- Put acid in burette (up to the 0cm3 mark), open tap and let it drip into the flask
- Once the liquid goes pink/red, stop and swirl the flask. If it stays the same colour - neutralisation has occurred. If not, continue adding until it does.
- Use moles to calculate the unknown concentration.
(concentration (mol/dm3) = moles / volume (dm3))
85
What is electrolysis?
Involves passing an electrical current through a substance to cause oxidation and reduction at the two electrodes - the anode (+) and cathode(-).
It can only take place if the ions are free to move to the electrode they're attracted to - so for ionic compounds, this can only happen when molten or in solution.
86
What is electrolysis used for?
It can be used to obtain pure metals from a compound/ore.
87
What are cations and anions attracted to?
Cations (+) are attracted to the cathodes (-) and anions(-) are attracted to the anode(+).
88
Which cation remains in the solution, the least or most reactive one?
The more reactive cation remains in solution, while the less reactive one is reduced at the cathode.
89
What gets oxidised at the anode?
Halide ions, ALWAYS. If the anion isn't a halide, the oxygen is oxidised instead and oxygen gas is produced.
90
Why does electrolysis in solution work?
Because the dissolved ions are free to move in the mixture.
91
Why does every chemical reaction involve energy changes?
Energy is needed to break chemical bonds, while it is released when bonds are made.
92
What is the difference between an exothermic and endothermic reaction?
An exothermic reaction is if a reaction intakes energy.
An endothermic reaction is if a reaction releases energy.
93
Describe the practical in which we find the max amount of alkali needed to neutralise an acid, through observing an endothermic reaction.
- React an acid with an alkali and measure the max temperature reached
- Repeat with increasing volumes of alkali and plot the volume of alkali used against the temperatures reached on a graph
- Eventually the max temp will start to decrease as the alkali is in excess.
- Draw two lines of best fit - one for the increasing temperatures and one of the decreasing temperatures
- Where these LOBFs meet is the volume of alkali needed to neutralise.
94
Describe the energy profile for an exothermic reaction.
- The potential energy of the reactants is higher than the potential energy of the products because there is a net increase in KINETIC energy.
- This increases temperature.
- Right before the potential energy decreases, there's an activation energy bump.
95
Describe the energy profile for an endothermic reaction.
- The potential energy of the reactants is lower than the potential energy of the products.
- The potential energy increases and then goes slightly above the pot energy of the products (activation energy from surroundings).
- The pot energy then goes down slightly again, and that's the pot energy of the products. A rise in the pot energy means a net decrease in kinetic energy, lowering the temperature.
96
What happens to the bonds in a reaction?
All the bonds are broken, then new ones are formed.
97
What do cells contain?
- Chemicals that, when reacted, produce a potential difference that can power electrical devices.
- They generally consist of two different metals in contact with an electrolyte.
98
What's the difference between non-renewable and renewable cells and batteries?
Non-renewable cells/batteries can't be used once their chemicals are used up.
Renewable batteries are able to perform the reverse reaction when a p.d. is supplied.
99
How do hydrogen fuel cells work?
They contain hydrogen and oxygen that haven been separated by electrolysis, for example. When they recombine, this produces a p.d. (voltage).
100
What is the rate of reaction?
Rate = change in quantity / time
This is technically the mean rate.
You can use mass/volume of reactant used/product made
101
Describe the X practical to show the rate of reaction.
- Place a flask on top of a paper with an X drawn on it.
- Put in the hydrochloric acid, then the sodium thiosulphate
- Start a timer
- The solution will go cloudy
- When you can no longer see the cross underneath the flask, stop the timer
- Record the time and repeat at different temperatures.
- Plot results on a graph, the gradient = rate of reaction
- Find the gradient using the calculation (y2 - y1 / x2 - x1
102
Describe the gas practical to show the rate of reaction.
- Put a reaction which produces gas into a flask
- Attach a gas syringe to the flask
- Measure volume of gas produced every 30s and note down results
- Plot results on a graph, the gradient = rate of reaction
- Find the gradient using the calculation (up / across)
| up/across of a triangle (so the opposite and adjacent)
103
How can you increase the rate of reaction?
Increase...
- The surface area
- Concentration
- Pressure
- Temperature
- Catalyst (reduces activation energy)
Increasing all of these makes particles collide more frequently, increasing temp makes the particles move faster and collide with more energy, and both increasing temp and adding a catalyst makes collisions more successful.
104
What happens in a reversible reaction in a closed system?
Both the forward and reverse reaction will take place. Eventually the rate of both reactions will be equal, reaching equilibrium. The overall quantity of both sides won't change.
105
What is Le Chatelier's principle?
If a system at equilibrium is subjected to a change, the system will adjust to counteract the change.
- Increasing pressure will favour the reaction that produces fewer moles.
- Lowering the concentration of one product will favour the opposite reaction.
- Increasing temperature favours the endothermic reaction because heat is needed for it.
106
What is crude oil made from and what does it consist of?
It's made from plankton buried underwater and compressed over a long time. It consists mainly of hydrocarbons (molecules made from **only** carbon and hydrogen).
107
What are the 2 types of hydrocarbons?
Alkanes and alkenes.
108
What are alkanes made of?
Single-covalently bonded carbon atoms surrounded by hydrogen atoms. They are SATURATED.
109
What is the general formula for alkanes?
CnH2n+2
110
What are the 4 alkanes you need to know?
C1 - Methane, C2 - Ethane, C3 - Propane, C4 - Butane
111
What does methane look like?
Like this:
H
|
H---C---H
|
H
This is methane.
112
Explain how the hydrocarbons in crude oil are made useful.
- They must be separated into fractions before they can be used.
- They're evaporated, and they rise up the fractionating column where they recondense at different heights: higher = colder
- Longer alkanes have higher boiling points due to more energy needed to overcome the stronger intermolecular forces, so they recondense lower down the column.
113
What are the hydrocarbon fractions?
| (in order of condensation)
- LPG
- Petrol
- Kerosene
- Diesel oil
- Heavy fuel oil
- Bitumen
114
What is the equation for complete combustion of alkanes?
fuel + oxygen ⇾ carbon dioxide + water
115
What is the equation for incomplete combustion of alkanes?
fuel + oxygen ⇾ carbon monoxide/carbon + water
Carbon monoxide is poisonous.
116
Different between long and short alkanes.
Longer alkanes have higher viscosity.
Shorter alkanes are more flammable.
117
What can hydrocarbons be used to make?
Solvents, lubricants, detergents and polymers (ALKENE ONLY).
118
What is an alkene?
A hydrocarbon with at least one double covalent bond, They are unsaturated.
119
What are the four alkenes you need to know?
- Methene
- Ethene
- Propene
- Butene
120
What are polymers made from? (used to make plastics)
Alkenes.
121
What is the general formula for alkenes?
CnH2n
122
How do you test for alkenes?
Adding bromine water will turn from orange to colourless. This is due to the bromine atoms bonding to the alkene by breaking the double bond into single bonds. The molecule has been saturated.
Chlorine and iodine react similarly, while water can react with an alkene to make an alcohol.
123
What does an alkene look like?
Like this:
H H
\| |
C==C
\| |
H H
This is ethene.
124
What is cracking?
The breaking of less useful hydrocarbon molecules into smaller, more useful ones.
125
Explain how cracking works.
- Takes places in an oil refinery in crackers.
- Within the cracker, a heavy fraction distilled from crude oil is heated to vapourise the hydrocarbons
- The vapour is then either: passed over a hot catalyst (at 550°C) OR mixed with steam and heated to a very high temperature
- Thermal decomposition reactions take place during cracking
| There must be the same number of all atoms in the products.
126
What is an alcohol?
An organic molecule with an -OH functional group.
| Names end in -ol.
127
What is the equation for complete combustion with alcohol?
alcohol + oxygen ⇾ carbon dioxide + water
128
What is the equation for incomplete combustion with alcohol?
alcohol + oxygen ⇾ carbon monoxide/carbon + water
129
Reacting ethanol + sodium produces what?
Sodium ethoxide + hydrogen.
130
Can alcohols produce a solution with water?
Yes! But this becomes more difficult the longer the alcohol.
131
What happens when alcohol is oxidised?
It produces a carboxylic acid (-COOH).
132
What does an alcohol look like?
.
H H
\| |
H---C---C---OH
\| |
H H
| This is ethanol.
133
What does a carboxylic acid look like?
H O
| //
H—C—C
| \
H OH
| This is ethanoic acid.
134
What is a polymer?
A long chained organic molecule of repeating sections made from monomers.
135
What is are monomers?
Small identical molecules.
136
What are the two types of polymerisation?
Addition and condensation.
137
Explain addition polymerisation.
The monomers are alkenes that need a C=C double bond, which break in order to produce a single bond to bond to the next monomer.
138
Explain condensation polymerisation.
The polymerisation of monomers that have two functional groups on the ends of the molecules. It forms the condensation polymer and a small molecule (typically water).
139
What do amino acids contain?
An amino group and a carboxyl group.
140
What can amino acids be polymerised to make?
Polypeptides and proteins.
141
What is DNA?
Deoxyribonucleic acid. It's a two-stranded polymer made from monomers called nucleotides.
142
What is starch a polymer of?
Glucose.
143
What is cellulose a polymer of?
Beta-glucose.
144
How do you test for pure substances?
Using their very specific melting/boiling points.
145
What is a formulation; provide examples?
Mixtures of certain quanitities of substances designed to fulfil a specific purpose.
- paints
- fuels
- alloys
- fertilisers
146
How do you test for the gases hydrogen, oxygen, carbon dioxide and chlorine?
Hydrogen - lit splint produces squeaky pop
Oxygen - will relight glowing splint
Carbon dioxide - causes limewater to turn cloudy when bubbled through it
Chlorine - bleaches blue litmus paper (making it white)
147
List the flame tests and their corresponding colours.
- Lithium - crimson
- Sodium - yellow
- Potassium - lilac
- Calcium - orange-red
- Copper - green
148
How do you test for metal ions in solution?
Add sodium hydroxide to make metal hydroxide (colour precipitate).
149
List the metal ion in solution tests and their corresponding precipitate.
- Aluminium/calcium/magnesium - white precipitate, which disappears with excess NaOH
- Copper ions - blue precipitate
- Iron (II) ions - green precipitate
- Iron (III) ions - brown precipitate
150
How do you test for carbonates?
React with an acid to produce CO2.
151
How do you test for halide ions and what precipitate do chloride, bromide and iodide ions produce?
You mix halide ions will produce a precipitate when mixed with silver nitrate and nitric acid.
- Chloride ions - white
- Bromide ions - cream
- Iodide ions - yellow
152
How do you test for sulphate ions?
Mix with radium chloride and hydrochloric acid to produce a white precipitate.
153
What is the instrumental method for flame tests?
Flame emission spectroscopy, which is *accurate, sensitive and rapid*.
It involves analysing the wavelengths of light emitted from a flame, which can be used to identify ions accurately.
154
What was the early earth's atmosphere made of? (timeline)
- Mostly CO2 with nitrogen and water, then increasing due to volcanic activity.
- The CO2 was likely then dissolved into the oceans formed, then into sediment.
- Plants and algae then converted the CO2 into oxygen.
155
What is the greenhouse effect?
It's what keeps the earth warm - greenhouse gases absorb long wavelength radiation reflected off the surface; including water vapour, CO2 and methane.
156
Define global warming.
The rise in global temperatures. The earth's climate is incredibly hard to model and predict, however.
157
What is carbon footprint?
The measure of how much CO2 is released into the atmosphere as a result of your actions.
158
What is carbon monoxide?
An atmospheric pollutant which binds to the haemoglobin in red blood cells, reducing the oxygen they are able to transport around the body. It's odourless and colourless, making it v/hard to detect.
159
Define sulphur dioxide.
An atmospheric pollutant which causes acid rain, which corrodes metals and erodes stone.
160
What is nitrogen oxide?
An atmospheric pollutant which causes respiratory problems.
161
Define carbon particulates/soot.
An atmospheric pollutant which causes health issues.
162
What are resources needed for?
- Warmth
- Shelter
- Food
- Transport
163
Give some examples of natural resources.
- Food
- Wood for building
- Fuels for burning, energy
- Materials for fabrics/clothing
164
How do we provide resources?
Through agriculture. However we are also trying to replace them with synthetic materials.
165
Define sustainability.
Using natural materials in a way that doesn't compromise future generations' ability to do the same.
166
What is potable water?
Water that has low enough levels of dissolved salts and microbes that it's safe enough to drink.
167
What is the easiest way of obtaining potable water?
Taking it from a freshwater source, filtering it then sterilising it using chlorine, ozone or UV.
168
What is desalination?
The removal of salt (from seawater) by distillation or reverse osmosis, so it's safe to drink. It unfortunately requires a lot of energy.
169
Why do we need to treat waste water?
To remove harmful chemicals and organic matter must be removed before it's released back into the environment.
170
Describe the process of treating waste water.
- Waste water is collected from the toilet or industrial processes
- The water goes through screening/grit removal
- Then it's put to rest - sedimentation
- The sludge is collected and anaerobically digested by bacteria
- The liquid effluent is aerobically digested
171
How do we obtain most metals?
From their ores, which are mined from the ground. Pure metal is then obtained by electrolysis or displacement reactions.
172
Name and explain two other ways metal is extracted.
Phytomining:
- Plants absorb copper ions into their roots.
- The plants are then burned, and the copper is obtained from the ash
Bioleaching:
- Bacteria produce leachate solutions that contain copper ions that can be extracted.
Both of these yield incredibly low amounts of copper though.
173
Explain life cycle assessments.
This predicts the impact of a new product on the environment.
LCAs consider...
- Extraction and processing of raw materials
- Manufacturing and packaging
- Use over its lifetime
- Disposal
- Transportation
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How do we reduce the impact of a new product on the environment?
- Use products less
- Reduce the materials and energy needed to make something
- Recycling
175
What is corrosion?
The destruction of metals over time due to chemical reactions.
176
What makes iron rust?
Water and oxygen (steel also does this).
177
What makes copper corrode?
When it reacts with oxygen to make copper oxide.
178
What colour is aluminium oxide?
White.
179
How do we protect important metals?
By covering them with sacrificial metals that will corrode before the important metal underneath does.
180
What is galvanising?
Covering another metal with zinc.
181
What is an alloy?
Mixture of metals to fulfil a specific need.
182
What is bronze?
An alloy made up of copper and tin.
183
What is brass?
An alloy made up of copper and zinc.
184
What is jewellery gold?
An alloy made up of gold, silver, copper and zinc.
24 carat = 100% gold.
18 carat = 75% gold, etc.
185
Define steel.
An alloy made up of iron and carbon.
186
Define stainless steel.
An alloy that's made up of steel and chromium/nickel.
| More resistant to corrosion than normal steel.
187
Why are alloys stronger than pure metals?
They are due to different size atoms disrupting the lattice, so their layers can't slide over each other easily.
188
When is aluminium used?
When we need to make light/low density alloys.
189
How is soda-lime glass made?
By heating sand, sodium carbonate and limestone.
190
How is borosilicate glass made?
From sand + boron trioxide. It has a higher melting point than soda-lime glass.
191
How is pottery made?
Made from heating shaped clay in a furnace.
192
Define composites.
A combination of two materials (except metals), with one binding the other, usually resulting in strong and light metals.
193
What is the difference between HDPE and LDPE?
HDPE is high density polyethene and LDPE is low density polyethene.
194
When heated, what happens to thermosoftening and thermosetting polymers?
Thermosoftening polymers melt when heated, and have a structure that is interlinked.
Thermosetting polymers don't melt when heated and have a structure which looks like bricks - these are cross-links between the polymers, which increases the attractive forces between the layers.
195
Explain the Haber process.
It makes ammonia.
- Nitrogen from the air is reacted with hydrogen from electrolysis of water.
- They're passed over a catalyst at a temperature of 450°C and a pressure of >200 atm.
The high pressure favours the forward reaction - the production of ammonia.
The higher temperature increases the rate of reaction but also favours the reverse reaction, which isn't good. ~400°C is a compromise temperature.
This maximises the yield of ammonia produced, while ensuring the reaction happens at a reasonable rate.
196
What is the equation for the Haber process?
N2 + 2H2 ⇌ 2NH3
197
What do plants need?
Nitrogen, phosphorus and potassium. To provide this, we make fertilisers from their salts.
| ^ NPK fertiliser
198
What is used to make ammonium salts?
Ammonia.
199
How are potassium chloride and potassium sulphate made?
Obtained by mining.
200
Can we use phosphate rock immediately?
No. You must mine it, then treat it with an acid before being added to the fertiliser.
