topic 9 - separate chemistry 2

Question 1

flame tests for metal ions

lithium
sodium
potassium 
calcium
copper (2+)

Answer 1

lithium ions - crimson flame
Sodium ions - yellow flame
potassium ions - lilac flame
calcium ions - orange-red flame
copper ions (Cu2+) - blue-green flame

Question 2

carrying out flame tests

Answer 2

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

Question 3

finding coloured precipitates of metal ions

aluminium 3+
calcium 2+
copper 2+
iron 2+
iron 3+

Answer 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

Question 4

working out if a substance contains ammonium ions

Answer 4

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

Question 5

testing for halide ions

Answer 5

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

Question 6

testing for carbonates

Answer 6

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

Question 7

testing for sulfate ions

Answer 7

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

Question 8

advantages of using instrumental analysis instead of conducting tests

Answer 8

tests that use machines, like flame photometry

• very sensitive
• very fast, the test can even be automated
• very accurate, don’t involve human error

Question 9

what can be tested for using bromine water

Answer 9

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

Question 10

what happens to hydrocarbons in combustion reactions

Answer 10

they are oxidised, both alkanes and alkenes

Question 11

what are polymers

Answer 11

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

Question 12

properties and uses of poly(ethene)

Answer 12

flexible, electrical insulator, cheap

plastic bags, bottles, wire insulation

Question 13

properties and uses of poly(propene)

Answer 13

flexible, mouldable, strong, tough

crates, furniture, ropes

Question 14

properties and uses of poly(chloroethene) - PVC

Answer 14

tough, cheap

window frames, water pipes

Question 15

properties and uses of poly(tetraflurorethene) PTFE

Answer 15

unreactive, tough, non-stick

non-stick pans, waterproof clothing

Question 16

condensation polymerisation

Answer 16

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

Question 17

formation of polyesters

Answer 17

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

Question 18

disposing of polymers in landfill sites

Answer 18

• 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

Question 19

disposing of polymers by combustion

Answer 19

• 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

Question 20

pros and cons of recycling polymers

Answer 20

+ 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

Question 21

dehydration reaction

Answer 21

when a mixture of an alcohol and an acid catalyst is heated together, an alkene and water are formed

Question 22

what happens when alcohols are oxidised

Answer 22

when alcohols are oxidised using an oxidising agent, they can form carboxylic acids

Question 23

working out which alcohol is best

Answer 23

• 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

Question 24

what are nanoparticles

Answer 24

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)

Question 25

uses of nanoparticles

Answer 25

catalysts - huge SA to volume ratio
sunscreen - small particles, better protection and no white cast
tiny electrical circuits - they conduct
surgical masks - silver nanoparticles are added to polymer fibres for surgical masks and wound dressings, they’ve the fibres antibacterial properties

Question 26

how are polymers suited for their purpose

Answer 26

they are adaptable - they’re often flexible and can be bent without breaking, easily moulded into almost any shape

cheaper than most materials

less dense

thermal and electrical insulators

can degrade and break down over time (bad)

Question 27

how are ceramics suited for their purpose

Answer 27

insulators of heat and electricity
more brittle and stiff than other materials
strong and hardwearing
don’t degrade or corrode

Question 28

how are metals suited for their purpose

Answer 28

good conductors of heat and electricity
malleable
some corrode easily, but there are corrosion resistant metals
not very brittle - may deform, but thy stay in one piece whilst other materials may shatter