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Flashcards in Topic 9 Deck (44)
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what do you use the flame test to identify

metal ions


what colour do the metal ions go in the flame test

lithium - red
sodium - yellow
potassium - lilac
calcium - red-orange
copper - blue-green


how do you carry out flame test

clean a nichrome wire loop by dipping it into hydrochloric acid and rinsing it in distilled water
dip wire loop into metal compound and put in clear blue part of flame


what is the test for metal hydroxides other than flame

add sodium hydroxide to metal compound and a precipitate will form because some metal hydroxides are insoluble
aluminium - white colourless in excess
calcium white
copper blue
iron 2 green
iron 3 brown


what is the test for ammonia

add sodium hydroxide
gently heat
damp red litmus blue


what is the test for halide ions

dliute nitric acid and silver nitrate
chlorine white
bromine cream
iodine yellow

nitric acid added first to get rid of any carbonate ions - they produce a pale precipitate with silver nitrate too which would confuse the results
you cant use HCl because you would be adding chloride ions


what is the test for carbonates

add dilute hydrochloric acid
mixture fizz because carbonate react with acid to form CO2
gas produced bubble through lime water and turn cloudy


what is the test for sulfate ions

add dilute HCl to stop ant precipitate reactions not involving sulfate ions from taking place and barium chloride
white precipitate will form of barium sulfate


what is flame photometry

- accurately identify different metal ions in a solution and their concentration
- instrumental method allowing you to identify ions in a solution
- each ion produces a unique line spectrum
- the intensity of the measured wavelength indicated the concentration of that ion in solution
- work out conc from a calibration curve
- it can be used to identify different ions in mixtures making it more useful than flame tests which only work for substances that contain a single metal ion


what are the advantages of using instrumental analysis like flame photometry

- very sensitive and can detect even the tiniest amounts of substances
-n very fast and tests can be automated
- very accurate as it removes human error


what are alkanes

- homologous series of hydrocarbons
- formula CnH2n+2
- saturates
- orange in bromine water


what are alkenes

- homologus series of hydrocarbons with one C=C functional group
- formula CnH2n
- unsaturated as can make more bonds as the double bond can open up
- colourless in bromine water as addition reaction takes place where bromine is added across the alkene double bond


what happens to hydrocarbons in combustion reactions

- they are oxidised
- alkanes and alkenes burn in oxygen in combustion reactions
- during complete combustion they're oxidised to form carbon dioxide and water

ethane + oxygen -> carbon dioxide and water
ethene + oxygen -> carbon dioxide and water


what is addition polymerisation

- polymers are substances of high average relative molecular mass made by joining small repeating units called monomers together
- the monomers that make up addition polymers have a double covalent bond
- lots of unsaturated monomer molecules (alkenes) can open up their double bonds and join together to form polymer chains. this is called addition polymerisation


what are the uses of polymers

plastic bags, bottles, wire insulation

crates, garden furniture, ropes

poly(chloroethene) (PVC):
window frames and water pipes

poly(tetrafluroethene) (PTFE):
nonstick pans and waterproof clothing


why are the properties of polymers

flexible, cheap, electrical insulator

flexible, strong, trough and mouldable

tough and cheap

unreactive, tough and nonstick


what is condensation polymerisation

- usually involves two different types of monomer
- the monomers react together and bonds form between them making polymer chains
- each monomer has at least two functional groups one on each end of the molecule
- each functional group can react with the functional group of another monomer creating a long chain of alternating monomers
- for each new bond that forms a small molecule (water) is lost


what are polyesters

- polyesters form when diacarboxylic acid monomers and diol monomers react together
- the diacarboxylic monomers contain two COOH groups (carboxylic acid groups)
- the diol monomers contain two alcohol (OH) groups
- when the carboxylic acid group reacts with the alcohol group it forms an ester link
- polyesters and condensation polymers
- each time an ester link is formed a small molecule of water is lost


what are three naturally occurring polymers

- contains two strands and each strand is made up of nucleotide monomers that bond together in a polymerisation reaction
- bases are different 4 nucleotide monomers

- made from amino acid monomers via condensation polymerisation

Starch and Cellulose:
- Carbohydrates are molecules containing carbon, oxygen and hydrogen used by living things to produce energy
- starch and cellulose are large, complex carbohydrates which are made up of many smaller units of carbohydrates known as sugars joined together in a long chain


what are polymers

p- plastics are a type of polymer made from crude oil
- crude oil is finite
- the more we use crude oil the more expensive it will become increasing the price of crude oil products
- crude oil is needed for petrol and heating are homes
- one way to fight this problem is recycling


discuss the problem of disposal of polymers

- when polymers are too difficult or expensive to separate and recycle
- lots of valuable land used up quickly
- most polymers are non-biodegradable (not broken down by microorganisms) meaning they will sit in landfills for years

- burning plastics produces a lot of energy which can be used to generate electricity
- if not carefully controlled toxic gases can be released from the combustion of plastics. For example when polymers that contain chlorine such as PVC are burned they produce HCl which has to be removed
- carbon dioxide produced contributing to global warming


what are the advantages of recycling polymers

- reduces the amount of non-biodegradable waste filling up landfills
- avoid environmental impact of burning/landfills
- limit the amount of crude oil we are using
- reduces emissions of greenhouse and toxic gases which can be released from burning polymers
- recycling generally uses up less water and energy resources than when making new plastics
- recycling generally saves money and creates jobs


what are the disadvantages of recycling polymers

- must be separated by type before they can be melted and reformed into a new product which can be difficult and expensive
- if polymers are mixed together the quality of the final recycled polymer product could be reduced
- polymers can only be recycled a finite number of times
- over time the strength of the polymer can decrease
- melting down polymers can release dangerous gases into the atmosphere
- these are harmful to plants and animals


what are the properties of alcohols

- general formula CnH2n+1OH
- can be oxidised to form carboxylic acids
- OH functional group


discuss alcohols be oxidised to form carboxylic acids

- you need an oxidising agent
- general formula Cn-1H2n-1COOH
- COOH functional group


discuss making ethanol by fermentation of yeast

- using yeast to convert sugar into alcohol
C6H12O6 -> 2C2H5OH + 2CO2
glucose -> ethanol + carbon dioxide

- sugar cane and sugar beet plants used
- yeast cells contain an enzyme to speed up reaction as biological catalyst

- mix yeast and glucose solution in clean container
- seal the container and leave in warm place
- keep mixture between 30-40 degrees as enzyme controlled reaction
- keep mixture in anaerobic conditions with no oxygen because otherwise the oxygen oxidises the ethanol to ethanoic acid which tastes vinegary
- when conc of alcohol reaches about 20% the fermentation reaction stops because the yeast is killed off by the alcohol
- yeast will fall to the bottom of the container and you can collect the ethanol solution from the top

- the fermented mixture can be distilled to produce a more concentrated alcohol


what is used to concentrate ethanol

fractional distillation
- a dilute solution of ethanol is produced by fermentation
- to make a conc above 20% ethanol must be concentrated by fractional distillation of the fermenting mixture
- fractional distillation separates mixtures by heating them
- ethanol has a lower boiling point than water so when the fermentation mixture is heated ethanol evaporates and vapour rises up the fractionating column while the water stays as a liquid
- a liebig condenser is used to condense the ethanol vapour by cooling it and the concentrated ethanol can then be collected in a separate flask


discuss alcohols been used as fuels

- alcohols can be used for fuel because when they are burned they release energy
- some countries that have littler or no oil deposits but plenty of land and sunshine grow loads of sugar cane which they ferment to ethanol and this ethanol is then used to help fuel cars


discuss the experiment to see which alcohol is the most efficient

- put 20ml of alcohol in a spirit burner and measure the mass of burner and fuel using a mass balance
- measure 100cm cubed distilled water into copper calorimeter
- insulate calorimater using a draught excluder then cover with an insulating lid after placing a thermometer inside to help reduce energy loss to the surroundings
- take the initial temperature of the water then put the burner under the calorimeter and light the wick
- stir the water throughout using the thermometer. When the heat from the burner has made the temperature of the water rise by 20 degrees blow out the spirit burner
- immediately reweigh the burner and fuel
- repeat the experiment using different alcohols but keep mass/volume of water, height of container above wick, length of wick/ height of flame and number of moles of alcohol the same


what means a better fuel

less alcohol burned

an alcohol will be more efficient as a fuel compared to another alcohol if less fuel is needed to raise the temperature of the water by a given amount

longer the carbon chain the more efficient the fuel will be