topic 9 - separate chemistry 2 Flashcards
flame tests for metal ions
lithium sodium potassium calcium copper (2+)
lithium ions - crimson flame Sodium ions - yellow flame potassium ions - lilac flame calcium ions - orange-red flame copper ions (Cu2+) - blue-green flame
carrying out flame tests
first clean a nichrome wire loop by dipping it in hydrochloric acid and then rinsing it in distilled water
then dip the wire loop into a sample of the metal compound and put the loop in the blue part of a bunsen flame
finding coloured precipitates of metal ions
aluminium 3+ calcium 2+ copper 2+ iron 2+ iron 3+
many metals hydroxides are insoluble and precipitate out of solution when formed
add a few drops of sodium hydroxide solution to a solution of the unknown compound
Al3+ = white at first, then redissolves to a colourless solution Ca2+ = white Cu2+ = blue Fe2+ = green Fe3+ = brown
working out if a substance contains ammonium ions
NH₄⁺
add sodium hydroxide solution to a solution of the mystery substance and heat gently - if ammonia gas is given off, there are ammonium ions in the substance
ammonia gas turns damp red litmus paper blue
testing for halide ions
chloride, bromide and iodide ions are tested for this way
add some dilute nitric acid to get rid of carbonate ions (they also produce a pale precipitate with siler nitrate so leave), then add a few drops of silver nitrate solution
chloride - white silver chloride precipitate
bromide - cream silver bromide precipitate
iodide - yellow silver iodide precipitate
testing for carbonates
add dilute acid, the mixture will fizz as CO2 is produced
to check if its CO2 it can be bubbled through limewater - it should turn it milky
testing for sulfate ions
add some dilute hydrochloric acid to the test sample (stops any precipitation reactions not involving sulphate ions from taking place)
then add some barium chloride solution, if sulphate ions are present then a white precipitate of barium sulfate will form
advantages of using instrumental analysis instead of conducting tests
tests that use machines, like flame photometry
- very sensitive
- very fast, the test can even be automated
- very accurate, don’t involve human error
what can be tested for using bromine water
alkenes, when shaken together an alkene will decolourise brome water
orange –> colourless because an addition reaction takes place and bromine is added across the alkene double bond
what happens to hydrocarbons in combustion reactions
they are oxidised, both alkanes and alkenes
what are polymers
substances of high average relative molecular mass, made by joining up lots of small repeating units called monomers
monomers that make up addition polymers are alkenes
properties and uses of poly(ethene)
flexible, electrical insulator, cheap
plastic bags, bottles, wire insulation
properties and uses of poly(propene)
flexible, mouldable, strong, tough
crates, furniture, ropes
properties and uses of poly(chloroethene) - PVC
tough, cheap
window frames, water pipes
properties and uses of poly(tetraflurorethene) PTFE
unreactive, tough, non-stick
non-stick pans, waterproof clothing
condensation polymerisation
two different types of monomer react together and bonds form between them, making polymer chains
each monomer has to contain a minimum of two functional groups, each functional group can react with the functional group of the other monomer, creating long chains of alternating monomers
formation of polyesters
polyesters form when dicarboxylic acid monomers and diol monomers react together
dicarboxylic acid monomers - contain 2 carboxylic acid groups (-COOH)
diol monomers - contain 2 alcohol groups (-OH)
when the carboxylic acid group reacts with the alcohol group, an ester link forms
polyesters are condensation polymers
disposing of polymers in landfill sites
- a lot of plastics are dumped in landfill - when different polymers are too difficult/expensive to separate and recycle
- lots of valuable land is quickly getting used up for landfill
- most polymers are non-biodegradable - they just sit in landfill
disposing of polymers by combustion
- burning plastic produces a lot of energy and can be used to generate electricity
- the burning has to be carefully controlled so that toxic gases can be released from the combustion of plastics
- CO2 is produced, a contributor to global warming
pros and cons of recycling polymers
+ reduced greenhouse and toxic gas emission from burning
+ recycling generally uses less water and energy than making new plastics
+ reduces amount of crude oil needed to produce more plastics
+ generally saves money and creates jobs
- polymers have to be separated by type first - can be difficult and expensive
- mixing polymers together - quality of final product is reduced
- polymers can only be recycled a finite no. of times - over time strength can decrease
- melting polymers down can release dangerous gases which are harmful to plants and animals
dehydration reaction
when a mixture of an alcohol and an acid catalyst is heated together, an alkene and water are formed
what happens when alcohols are oxidised
when alcohols are oxidised using an oxidising agent, they can form carboxylic acids
working out which alcohol is best
- add some alcohol to a spirit burner and measure mass (wear safety glasses and gloves)
- 100cm^3 into a copper calorimeter
- insulate the calorimeter with a drought excluder, cover with an insulating lid after placing a thermometer inside
- take initial water temp, put the burner under the calorimeter and light the wick
- stir the water using the thermometer, when the heat rises by 20˚~C blow out the burner
- immediately reweigh
- smaller change in mass = more efficient fuel
what are nanoparticles
tiny particles, around 1-100 nm across
they contain roughly a few hundred atoms, so they’re bigger than atoms
they have very different properties from the bulk chemical that they’re made from (because of their high surface area to volume ratio)
