Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Qualitative analysis: tests for ions
Why test for ions must be unique – Gives certain results depending on ion present
Identifying positive ions
Flame tests
Clean nichrome wire loop: dip into hydrochloric acid & rinse with distilled water
dip into metal compound sample & place in clear part of flame (hottest)
lithium Li+ red
sodium Na 2+ yellow
potassium K+ lilac
calcium Ca2+ orange-red
copper Cu2+ blue-green
Cause of colour
Electrons move to higher energy levels – when they return, they release energy as visible light
(coloured)
Precipitation reactions by adding sodium hydroxide solution
Tested metal will become insoluble hydroxide: precipitate – use colour to identify
Aluminium Al3+ white then colourless when dissolved in excess sodium hydroxide
Calcium Ca2+ white
copper Cu2+ blue
iron(II) Fe2+ green
iron(III) Fe3+ brown
ammonium NH4+ gives off ammonia gas when heated: should turn red litmus paper blue
+ sharp smell
Identifying negative ions
2Carbonate CO3 : dilute acid → carbon dioxide gas
Metal carbonate + acid → salt + water + carbon dioxide
Sulfate SO42-: dilute hydrochloric acid + barium chloride solution → barium sulfate precipitate
(insoluble white solid)
Halide ions: dilute nitric acid (first: remove carbonate ions) + silver nitrate solution
Chloride Cl2- white precipitate
Bromide Br2- cream precipitate
Iodide I2- yellow precipitate
instrumental methods of analysis improve:
Sensitivity: detect smallest amounts of substances
Speed – can be automated
Accuracy: no human error
Flame photometry – instrumental method: looks at light emitted from solution of metal ions
identify metal ions in sample
Coloured light from vaporised sample can be split to produce emission spectrum
Each metal ion has unique emission spectrum
Identify metal by comparing sample to reference spectra
Determine concentration of metal ions in dilute solutions
Readings taken from flame photometer for known concentrations of metal ion in solution – used to
plot calibration curve (measure of emitted light / concentration)
Compare with calibration curve of known concentrations

Hydrocarbons – homologous series
Homologous series: group of chemicals that have similar chemical
structures
Functional group: group of atoms that determine how a molecule
reacts
Members of homologous series all contain same functional group
Saturated hydrocarbons:
All atoms form bonds with as many other atoms as they can
Each line: covalent bond
Alkane: CnH2n+2
Methane: CH4
Ethane: C2H6
Propane: C3H8
Butane: C4H10
Unsaturated hydrocarbons:
they can make more bonds – double bond can open up
Alkene: CnH2n – homologous series of hydrocarbons
with C=C functional group
Ethene: C2H4
Propene: C3H6
Butene: C4H8
But-1-ene & but-2-ene: which ‘C’ – double bond goes after
Bromine water addition
Test for carbon=carbon double bond (alkene)
Alkene: orange to colourless – decolourisation
Alkane: remains orange
Complete combustion of alkanes/alkenes: involves oxidation of
hydrocarbons to produce CO2 + H2O

Polymers
Substance of high average relative molecular mass made up of small repeating units (monomers)
Addition polymerisation
Made from unsaturated monomers – double covalent bond
Poly(ethene): Double bond breaks open to allow more ethene molecules to join together into single product
Properties depend on arrangement of polymer chains and forces between them
Poly(ethene): Flexible, cheap
Plastic carrier bags, cling film
Poly(propene):
Flexible, strong, resists shattering
Buckets, bowls, crates, carpets, ropes
Poly(chloroethene) (PVC): Tough electrical insulator, flexible or hard
Insulation for electrical wires, windows, gutters, pipes
Poly(tetrafluoroethene) (PTFE):
Slippery, chemically unreactive
Non-stick coating for pans, containers for laboratory substances
Condensation polymerisation
Involves 2 types of monomer
Monomers react / form bonds between them – forming polymer chains
Each monomer contains at least 2 functional groups – one at each end
Each functional group reacts with functional group of another monomer – creates long chain of alternating
monomers
For each new formed bond – water molecule lost
Polyester: condensation polymer – each time an ester link is formed – a water molecule is lost
Formed when dicarboxylic acid monomers & diol monomers react together
Dicarboxylic acid monomers contain 2 carboxylic acid groups (-COOH)
Diol monomers contain 2 alcohol groups (-OH)
Carboxylic acid group + alcohol group = ester link
Problems
Made from crude oil: will begin to run out & become more expensive – needed for country’s energy
landfill sites: non-biodegradable – waste of land for innumerable years
Combustion: produces CO2
Sorting polymers to be recycled is expensive/difficult
Recycling
Advantages
Reduces amount of plastic in land fill
Reduces emissions from combustion
Uses less water /money / energy resources than
making new plastics
Creates jobs
DNA: 4 monomers – nucleotides

Disadvantages
Difficult/expensive to separate polymers by type
Mixed polymers reduces quality of product
Polymers can only be recycled limited number of
times – strength will decrease
Melting polymers can release dangerous gases

Proteins: based on amino acids

Starch: based on sugars

Alcohols and carboxylic acids
Alcohols: methanol 1, ethanol 2, propanol 3, butanol 4
Formulae: CnH2n+1OH
functional group: –OH
Alcohol form alkenes when dehydrated – each alkene molecule formed: water molecule lost
Ethanol with acid catalyst & heat → ethene + water
Core Practical: Investigate temperature rise produced in known mass of water by combustion of
alcohols
Used as fuel: release energy when burned
Experiment to see which alcohol is best fuel
Less alcohol burned = better fuel
More efficient if less fuel is needed to raise temperature of water by same amount
The longer the carbon chain: the more efficient
Put alcohol into spirit burner – measure its mass with fuel
100cm3 into copper calorimeter
Insulate using draught excluder, cover with insulating lid with thermometer inside – ensure
minimal energy lost to surroundings
Measure initial temperature of water then place it above burner & light wick
Stir water throughout
Blow out burner when water’s temperature has raised by 20˚
Reweigh burner with fuel immediately
Repeat with all alcohols keeping: volume of water / height of container above burner / length of wick /
moles of alcohol the same
Ethanol made by fermentation in lab
Uses yeast’s enzymes to convert sugars into alcohol
Mix yeast with solution of carbohydrate in container – leave in warm place (30-40˚C – fermentation
happens fastest)
Must be kept without oxygen or it would convert the ethanol to ethanoic acid
When concentration of alcohol reaches 10-20%: fermentation stops – alcohol kills off yeast
Yeast falls to bottom of container so you can collect ethanol solution from top
Fractional distillation of ethanol solution (from fermentation) to make it more concentrated
Ethanol has lower boiling point than water: it evaporates – water remains as liquid
Ethanol vapour rises in fractioning column and passes through Liebig condenser – converted back to liquid
and collected
Carboxylic acids: methanoic, ethanoic, propanoic, butanoic
functional group: –COOH
carboxylic acids have acidic properties:
react with carbonate to produce: carbon dioxide + salt + water
when in solution: ionise and release hydrogen ions – partially ionise: weak acids
Produced by oxidising alcohol
members of homologous series contain same functional group – have similar reactions

Bulk and surface properties of matter – nanoparticles
Compare size of nanoparticles with the sizes of atoms and molecules
1nm = 1 x 10-9m
Contain a few hundred atoms
Bigger than simple molecules
Fullerenes are nanoparticles
High surface area:volume ratio: gives nanoparticles different properties to ‘bulk’ chemical it’s from
grater proportion of atoms available to interact with substances that come in contact
nanoparticulate material proportions in relations to their uses – surface area:volume ratio of particles they contain
Sunscreens – titanium dioxide: doesn’t leave white marks on skin – small size, absorbs UV
Nano-medicine: fullerenes absorbed more easily
Lubricant coatings using fullerenes: artificial joints / gears
Nanotubes: conduct electricity, used in tiny electric circuits
Make plastics more strong/durable without adding mass – sports equipment
Silver nanoparticles added to polymer fibres: gives them antibacterial properties – surgical masks / wound dressing
Huge surface area to volume ratio: good catalysts – reactions take place on surface of catalyst: more collisions with
surface = faster rate of reaction
risks of nanoparticulate materials
Don’t break down easily – build up in cells
Side-effects/long-term impacts not known – new technology
Small size – breathed in / pass through membranes
Can catalyse harmful reactions
Properties & suitability of materials
Polymers
Strong/rigid
light/stretchy
Adaptable – bent without breaking & moulded into any shape
Cheap
Less dense – used for products that need low mass
Thermal/electrical insulators
Degrade/breakdown – don’t last long
Ceramics
Insulate heat/electricity
Brittle
Strong/hard-wearing
Don’t degrade/corrode – last long
Clay
Mineral – formed from weathered/decomposed rock
Soft – easy to mould
Hardened with high temperatures

composites
Fibreglass/concrete
Made from one material & embedded in another
Expensive
Can be designed to have specific properties for specific purpose
Metals
Conduct heat/electricity
High-density
Malleable – variety of shapes
Some corrode – some corrosion resistant
Less brittle – likely to deform but won’t shatter
Can be mixed with other elements to form alloys

poly(styrene) foam

heat-resistant

Glass
Transparent/strong
Moulded when hot
Brittle when thin
Soda-lime glass: made by heating
limestone / sand / sodium carbonate



---