Chemistry Paper 2

- system is no longer at equilibrium
- concentration of all substance will change until equilibrium is reached agin
- if concentration of reactant is increased, more products will be formed until equilibrium

in the exothermic direction - to release heat and minimise temp change

to the side with the fewest mols of gas - to oppose the increase

don't change position, only increase rates of forwards and backwards reactions

all changes to a system are opposed by a shift in equilibrium

- position of equilibrium moves to the product side to decrease the concentration of A
- A reacts with B, so the concentration of B decreases

CnH2n+2

- low BP
- higher volatility (tendency to turn into a gas)
- low viscosity (how easily it flows)
- higher flammability

turns blue cobalt chloride paper pink

CO formed because there isn't enough oxygen

- crude oil is heated
- vapours pass over a hot catalyst

vapours are mixed with steam and heated to a very high temperature

turn orange bromine water colourless

'family' of organic compounds with same functional group

CnH2n

- burn with a smokier yellow (luminous) flame compared with alkanes because there is incomplete combustion
- also release less energy per mole in combustion so aren't used as fuels

ethene + oxygen => carbon dioxide + water

- much more reactive than alkanes due to c=c bond
- molecules that react with alkenes 'add' to them across their double bond

60*C in presence of a nickel catalyst

- adding hydrogen across the c=c bonds in unsaturated oils straightens their molecules and increases MP
- the right amount of hydrogen can be added to make margarine that is easily spread straight from the fridge

- ethene gas reacted with steam
- ethene gas is the main by-product of cracking
- reaction requires energy to heat gases and generate high pressure
- reversible reaction - ethanol can break back down into ethene and steam so unreacted are recycled over the catalyst

-OH

-COOH

-COO-

fermenting sugars from plant material with yeast

dissolve many other organic compounds

- alcohols dissolve many of the same substances as water
- alcohols with smaller molecules mix very well with water, giving neutral solutions

- mainly ethanol but have the more toxic methanol mixed with them
- purple dye and other substances added make it unpleasant to drink

- 'clean' blue flame
- used in spirit burners and as biofuel in cars

carbon dioxide + water

- similar reaction to water
- forms sodium alkoxide solution and gives off hydrogen gas
- sodium alkoxides form strongly alkaline solutions when dissolved in water

oxidised by chemical oxidising agents or by action of microbes in the air

dissolve in water so that they can ionise

weak - most molecules stay as they are and don't ionise

CO2 is given off slowly, due to high pH of the weak carboxylic acid

ester + water

- distinctive smells - ideal for food flavourings
- volatile - ideal for perfumes

strong, easy to shape and transparent - used in carrier bags, cling film etc

very strong and tough plastic - used in carpets, milk crates and ropes

- alkene molecules join together
- double covalent bond between 2 carbon atoms in each alkene molecule 'opens up'
- replaced by a single carbon-carbon covalent bond between the two carbon atoms
- thousands of molecules can join together end to end

C=C double bond

an addition polymer

an condensation polymer and a small molecule (usually H2O or HCl)

- addition - monomers used often all the same alkene
- condensation - often 2 different monomers used with 2 different functional groups

diol + dicarboxylic acid ---> polyester + water

an alcohol containing 2 -OH groups

carboxylic acid containing 2 -COOH groups

- 2 monomers react together and give of HCl(g) as a small molecule
- monomers have reactive parts at both ends of their molecules so join together end-to-end, forming a long nylon polymer chain

- monosaccharides - made up of one sugar unit
- polysaccharides - repeating sugar units

- glucose = 6-membered ring structure
- fructose = 5-membered ring structure

1 glucose + 1 fructose

- 2 functional groups in the same molecule
- 1 basic (the amine group -NH2)
- 1 acidic (the carboxylic acid group -COOH)
- because acids and bases react together, amino acids have potential monomers with reactive groups at each end

react together in condensation polymerisation to make polypeptides and proteins made of long sequences of different monomers

- double helix made up of 2 long polymer strands of nucleotides
- 2 strands run in opposite directions to each other and are held in place by the intermolecular forces down the length of each polymer strand
- 4 different nucleotide monomers can react with each other to form DNA polymers
- nucleotides are based on the sugar deoxyribose, bonded to a phosphate group and a base (4 possible bases)

mixture that has been designed as a useful product - components are mixed in measured quantities

- mobile phase (solvent) moves through the stationary phase (paper), carrying the components of the mixture with it
- each component has a different attraction for mobile and stationary phases
- substance with greater attraction between itself and the mobile phase moves a greater distance

$\frac{Distance \space moved \space by \space substance}{Distance \space moved \space by \space solvent}$

squeaky pop - burning splint held at the open end of a test tube burns rapidly with a pop sound

relights a glowing splint

bleaches damp litmus paper white

- dip nichrome wire loop in concentrated HCl, heat, and then dip back into acid
- dip into metal compound being tested
- hold loop in roaring blue flame of bunsen burner
- identify metal ion by flame colour
- some flame colours can be masked if the sample contains a mixture of metal ions

Li$^+$, crimson flame

Na$^+$, yellow flame

K$^+$, lilac flame

Ca$^2+$, orange-red flame

Cu$^2+$, green flame

- Al3+, Ca2+ and Mg2+ form white precipitates with sodium hydroxide solution
- if more sodium hydroxide is added, the precipitate formed with Al3+ ions will dissolve
- Ca2+ and Mg2+ can be distinguished by a flame test
- Ca2+ = orange-red flame
- Mg2+ = colourless flame

- Cu(ii) = blue precipitate
- Fe(ii) = green precipitate
- Fe(iii) = brown precipitate

- add dilute acid, which produces CO2 gas
- CO2 turns limewater cloudy
- group 1 carbonates dissolve in water

- add dilute nitric acid, then silver nitrate solution
- if a precipitate forms, hallide ions are present
- nitric acid purpose - dissolves compound and removes any carbonate ions as they would also form a precipitate with the silver ion, interfering with the test

I$^-$, yellow precipitate with silver ions

Br$^-$, cream precipitate with silver ions

Cl$^-$, white precipitate

- add dilute HCl to remove carbonate ions that would interfere
- add barium chloride solution
- positive = white precipitate of barium sulfate

- fast
- accurate
- enable very small samples to be analysed

- expensive
- special training needed
- results can often be interpreted only by comparison with data from known substances

- used to indentify metal ions
- sample put into a flame
- energy makes the metal ion electrons jump to higher energy levels
- when they fall back to lower levels, the energy is released as light energy
- the wavelengths of the light are analysed by the spectroscope
- each type of metal ion absorbs and gives out a characteristic line spectrum (pattern of radiation)

concentration of metal ions can be tested by measuring the intensity of the light

using solutions of the metal ion of known concentrations to give a value for the unknown concentration

steel industry - carefully control amounts of trace metals present to ensure quality of steel

- 80% nitrogen
- 20% oxygen
- <1% CO2, water vapour, noble gases

- volcanoes released CO2, H2O vapour and N2
- H2O vapour condensed and fell as rain - oceans
- mainly CO2 and little / no O2(g)
- may have been a bit of methane and ammonia
- N2 amount gradually built up - very unreactive so didn't react with O2 like methane and ammonia

- algae produced O2 - gradually increased until animals could evolve
- CO2 also reduced by formation of sedimentary rocks and fossil fuels that contain carbon

thick deposits of plant material eg. ancient trees and ferns

plankton

- greenhouse gases let short-wavelength EM radiation through
- surface of Earth cools down by emitting longer wavelength infrared radiation
- greenhouse gases absorb infrared
- radiation stimulates the molecules to vibrate and bend and stretch more vigorously - raising their temperature

less soluble in water

total amount of CO2 and other greenhouse gases emitted over the full life cycle of a product, service or event

swamps, rice fields, cattle

CO2 produced in fossil fuel power stations could be pumped deep underground and absorbed into porous rocks

high temperature inside allows the normally unreactive nitrogen gas in air to react with oxygen

- diesel engines burn bigger molecule hyrdocarbons than petrol
- when these large molecules react with oxygen they don't burn completely
- so tiny solid particles containing carbon and unburnt hydrocarbons produced

colourless and odourless

- travel into upper atmosphere and reflect sunlight back into space (global dimming)
- some scientists think they might damage lung cells and cause cancer

being used up at a faster rate than they can be replaced

from ethanol - fermenting glucose from natural resources of renewable crops / raw materials

- rainwater seeps through soil and rocks to porous underground seams of rock
- fresh water can be obtained by drilling a pipe down to form a water well

- rainwater dissolves some gases from the air as it falls
- on solid ground, it dissolves soluble substances as it passes over them
- water from natural sources will always contain dissolved minerals (salts) and microorganisms from the soil / decaying matter

- pass untreated water through filter beds of sand and gravel to remove solid particles
- add chlorine / ozone / UV to sterilise by killing microorganisms

- converting salty water to potable and useable water
- flash distillation and reverse osmosis

reduce pressure so water boils below 100*C

- membranes separate water from salts dissolved in it
- no heating needed but still energy to pressurise water passing through
- corrosion of pumps by salty water adds expense

- screening
- primary treatment
- secondary treatment
- final treatment
- (additional treatment)

passes through metal grid that traps large solid objects and grit

- solid sediments allowed to settle out from the mixture
- large paddles rotate, pushing the sludge towards the centre of the tank
- sludge is piped to a storage tank for further treatment
- watery liquid (effluent) above the sludge flows into next tank

- useful bacteria aerobically break down any remaining organic matter and harmful microorganisms
- tank is aerated by bubbling air through water

- useful bacteria are allowed to settle out to the bottom of the tank as sediment
- sediment is either recycled back into secondary tank or passed into tank where sludge is treated
- safe to discharge back into rivers

- if river is particularly sensitive ecosystem, water can be filtered agian through a bed of sand
- can then be sterilised by chlorine / UV
- but toxic organic compounds of chlorine can be formed in the environment

- most can be dried and used as fertiliser / renewable energy
- organic matter in the sludge is digested anaerobically by microorganisms
- breakdown products - biogas to power treatment plant / surrounding area
- biogas can be further cleaned to make methane and piped into gas supply
- sludge can be dried out and turned into crusty solid 'cake' that can be burnt to generate electricity

copper-rich ores - finite resource in danger of running out

- copper sulfate solution produced
- copper extracted by adding scrap iron - displacement

- copper ore heated to a high temperature in a furnace with air to produce impure copper
- impure copper then used as the positive electrode in electrolysis cells to make pure copper

- plants that can absorb copper ions are grown on soil containing low-grade copper ore
- could be slag heaps of previously discarded waste from processing copper-rich ores
- plants are burnt
- copper ion 'leached' (dissolved) from the ash by adding sulfuric acid - solution of copper sulfate
- displacement by scrap iron then electrolysis makes pure copper

- bacteria feed on low-grade ores
- by a combo of biological and chemical processes, a solution of copper ions can be obtained from waste copper ore
- scrap iron and electrolysis used to extract pure copper

- list all energy and material inputs and all outputs into environment
- evaluate possible environmental impacts of these
- data often converted into a single 'impact score' - requires subjective judgement
- calculations based on assumptions should include an uncertainty (+-)
- don't take into account differences in cost / performance

- help conserve Earth's reserves of aluminium ore
- save energy by avoiding electrolysis

- source of scrap iron (usually steel cans with thin coating of tin to prevent rusting)
- magnetic - easy to separate in waste centres

often alloyed with other metals

- huge pits scar landscape, create noise and dust, destroy habitats
- mines leave large heaps of waste rock
- as rain drains through exposed ores and slag heaps of waste, groundwater can become acidic
- sulfide ores heated in smelting can produce sulfur dioxide gas

caused by the chemical reactions between a metal and substances in the environment

corrosion of iron - forms on surface and soon flakes off, exposing more iron

no - protected by the oxide layer that forms on its surface

air and water

paint, oil / grease, plastic, less reactive metal

- iron is coated in zinc (more reactive)
- any water / oxygen reacts with zinc
- iron is galvanised (protected from oxidation)
- magnesium / aluminium can also be used
- used when iron is in contact with seawater, in underground pipes and where coating is likely to be scratched off eg. wheelie bins

- copper and tin
- tough and resistant to corrosion
- statues and ship propellors

- copper and zinc
- can be hammered and shaped but stronger than copper
- musical imstruments and taps

lightweight but strong - aluminium has a low density for a metal

- usually alloyed with copper to make jewellery
- proportion of gold in alloys is measured in carats

strong but brittle

soft and more easily shaped

much cheaper and simpler than ones with other metals

- chromium-nickel steels
- hard, strong and resistant to corrosion
- used in cutlery and reaction vessels in the chemical industry

- formed from ethene at moderate temperature and high pressure
- polymer chains are randomly branched and can't pack closely together

- made from ethene at lower temperature and pressure with a catalyst
- straighter chains - can pack more closely together than branched chains
- stronger and higher softening temperature than low density

- tangled web of polymer chains
- weak intermolecular forces between chains
- becomes soft on heating
- when cooled down - intermolecular forces bring chains back together and polymer hardens again - so polymer can be remoulded

- strong covalent bonds forming 'cross links' between chains - can't separate
- monomers make covalent bonds between chains when first heated to shape the polymer
- even if heated strongly, polymer won't soften
- will eventually char at a high enough temperature

- raw materials are heated - melt and react to form molten glass, then cooled down to form a solid
-particles don't form a regular pattern (as if the molten glass particles are frozen in place)

- soda glass (sand, limestone and soduim carbonate)
- borosilicate glass (sand and boron trioxides) - melts at higher temperature than soda glass so used in ovenware and test tubes

- clay contains compounds of metals and non-metals (ionic) but also has some covalent bonding
- the ions and atoms are arranged in giant structures that form layers
- when clay is wet, water molecules get between the layers and make it mouldable
- when heated in a furnace, water is driven out and strong bonds form between layers
- the higher the furnace temperature, the harder the ceramic formed

a sharp blow can distort layers in their structure so that ions with like charges are adjacent and repel each other

one material acts as a binder for the other, surrounding and binding together fibres / fragments

- fine threads of glass embedded in a polymer resin that hardens once moulded into shape
- tough, flexible, waterproof, low density - kayaks

thin sheets of wood glued together so grain run in layers at right angles to each other - split resistant

woodchips and shavings compressed together and bound with polymer resin - cut into intricate shapes without splintering

- cement, sand and gravel mixed with water and left to set
- can be made more resistant to bending forces by setting it around a matrix of steel rods

plants take in soluble nitrate ions (NO3-) as they grow but this isn't naturally cycled in farming because most parts of the plant aren't allowed to rot back into the soil

- nitrogen and hydrogen purified
- passed over an iron catalyst at around 450*C and around 200 atmospheres
- reversible reaction - ammonia gas made breaks down again into nitrogen and hydrogen
- ammonia removed by cooling the gases so that ammonia liquefies and can be separated from unreacted gases
- unreacted gases are re-compressed, heated and recycled back into the reaction mixture

- nitrogen extracted by fractional distillation of liquid air - energy required to significantly cool down air
- hydrogen obtained from reacting methane gas with steam at very high temperature - energy needed and methane gas is expensive

- side with the least moles of gas = right hand side
- so position of equilibrium will move to the right and produce more ammonia, in order to reduce the pressure
- higher pressure = higher yield
- but high pressure - lots of energy to compress gases and expensive reaction vessels and pipes - strong enough to withstand pressure
- compromise of 200 atmospheres

- forwards reaction is exothermic
- lower temperature - position of equilibrium moves to exothermic direction to release heat and minimise temperature change
- but low temperature = slow rate of reaction - running a chemical plant is expensive so reaction should happen quickly
- low temperature also reduces effectiveness of iron catalyst
- compromise of $450\degree C$

yes but most is turned into compounds of ammonia

nitric

- can be made by reacting ammonia solution (alkali) with different acids
- sulfuric acid - ammonium sulfate
- nitric acid - ammonium nitrate
- phosphoric acid - ammonium phosphate

nitrogen, potassium and phosphorus all added to land at same time in mixture of compounds

- comes from deposits of phosphate-containing rock
- rock can't be used directly on soil - insoluble in water
- must be treated with acids to make fertiliser salts (ammonium phosphate and calcium phosphate)