Topic 9 - seperate chemistry 2

explain why the test for any ion must be unique

• you would never be able to know which specific ion it was if more than one ion gave you the same result

colour of flame test for lithium ion, Li+

red

colour of flame test for sodium ion, Na+

yellow

colour of flame test for potassium ion, K+

lilac

colour of flame test for calcium ion, Ca²⁺

orange-red

colour of flame test for copper ion, Cu²⁺

blue-green

what will form from tests to identify aluminium ions, Al³⁺ in solids or solutions

white precipitate (dissolves when excess NaOH is added

what will form from tests to identify calcium ions, Cu²⁺ in solids or solutions

white precipitate

what will form from tests to identify coper ions, Cu²⁺ in solids or solutions

blue precipitate

what will form from tests to identify iron (II) ions, Fe²⁺ in solids or solutions

green precipitate

what will form from tests to identify iron (III) ions, Fe³⁺ in solids or solutions

brown precipitate

what will form from tests to identify ammonium ions, NH⁴⁺ in solids or solutions

• pungent smelling gas is produced

• this gas produced turns damp red litmus paper blue

describe the chemical test for ammonia

• makes damp red litmus paper turn blue

• it also forms a white smoke of ammonium chloride when hydrogen chloride gas, from concentrated hydrochloric acid, is held near it

describe tests to identify the following ions in solids or solutions as appropriate

• carbonate ion, CO₃^2- , using dilute acid and identify the CO₂ evolved

  • gas produced bubbled through limewater, if the limewater goes cloudy, the gas is CO₂ (carbonates react with dilute acids to produce CO₂)

• sulfate ion, SO₄^2-, using dilute hydrochloric acid and barium chloride solution

  • add dilute HCl followed by barium chloride solution

  • a white precipitate will form when sulfate ions are in this solution

• chloride ion, Cl^-, bromide ion, Br^-, iodide ion, I^-, using dilute nitric acid and silver nitrate solution

  • first add dilute nitric acid, followed by silver nitrate solution

  • chloride gives a white precipitate

  • bromide gives a cream precipitate

  • iodide gives a yellow precipitate

describe that instrumental methods of analysis are available and that these may improve sensitivity, accuracy and speed of tests

• elements and compounds can be detected and identified using instrumental methods

  • these are accurate, sensitive and rapid

• instrumental methods include: gas chromatography and mass spectrometry

evaluate data from a flame photometer to determine the concentration of ions in dilute solution using a calibration curve, and to identify metal ions by comparing the data with reference data

• examples of an instrumental method used to analyse metal ions in solutions

• sample is put into a flame and the light given out is passed through a photometer

• output is a line spectrum that can be analysed to identify the metal ions in the solution and measure their concentration

formula of molecules of the alkanes and draw structures of these molecules showing all covalent bonds

• the first 4 alkanes are methane, ethane, propane and butane (Monkeys, Eat, Peanut Butter)

• alkane molecules can be represented in the following forms:

  • C₂H₆

explain why the alkanes are saturated hydrocarbons

they contain no C=C double bonds and are compounds made of hydrogen and carbon only

recall the formulae of molecules of the alkenes, ethene, propene, butene and draw the structures

• the first 2 alkenes are ethene and propene

• unsaturated carbons can be represented in the following forms:

explain why the alkenes are unsaturated hydrocarbons

• contain one or more C=C double bonds and are compounds made of hydrogen and carbon only

recall the addition reaction of ethene with bromine, showing the structures of reactants and products, and extend this to other alkenes

• ethene + bromine → 1,2-dibromethane

• this reaction works the same for any alkene or any halogen

explain how bromine water is used to distinguish between alkanes and alkenes

• alkenes react with bromine water, turning it from orange to colourless - alkanes DO NOT react with bromine water

what does the complete combustion of alkanes and alkenes involve

• the combustion of hydrocarbons releases energy

• during combustion, the carbon and hydrogen in the fuels are oxidised to produce carbon dioxide and water

• alkane/alkene + oxygen → carbon dioxide + water

what is a polymer

• a polymer is a substance of high average relative-molecular mass made up of small repeating units

what happens if ethene molecules combine together in a polymerisation reaction

• alkenes can be used to make polymers such as poly(ethene) and poly(propene) by addition polymerisation. in this reaction, many small molecules (monomers) join together to create very large molecules (polymers) — eg. in photo

• the repeat unit has the same atoms as the monomer because no other molecule is formed in the reaction

describe how other addition polymers can be made by combining together other monomer molecules containing C=C, to include poly(propene), poly(chloroethene) and poly(tetrafluoroethene)

• any alkene can be used as a monomer to create a polymer due to the C=C bond

deduce the structure of a monomer from the structure of an addition polymer and vice versa

• monomer is the same as the repeat unit, just replace C-C with C=C and remove brackets and ‘n’

how are poly(ethene)s properties related to its uses

• properties: flexible, cheap, electrical insulator

• uses: plastic bags and bottles, coating on electrical wires

how are poly(propene)s properties related to its uses

• properties: flexible and strong

• uses: buckets and crates

how are poly(chloroethene/PVC)s properties related to its uses

• properties: tough, cheap and long lasting

• uses: window frames

how are PTFEs properties related to its uses

• properties: tough & non-stick

• uses: non-stick coating on pans

explain why polyesters are condensation polymers

• in condensation polymerisation, a small molecule is formed as a by-product each time a bond is formed between two monomers

• alcohol and carboxylic acid functional groups react, losing a small molecule - water

• this is an ester - therefore a polyester is a lot of these monomers (esters)

explain how a polyester is formed when a monomer molecule containing two carboxylic acid groups is reacted with a monomer molecule containing two alcohol groups

• the dicarboxylic acid loses the OH group off of each COOH group

• the di-alcohol loses the H off of each OH group

• the remaining molecules join together to make a polyester

explain how a molecule of water is formed each time an ester link is formed

• the OH and H groups combine to make H₂O

describe some problems associated with polymers

• polymers are formed by the joining up of many small molecules with strong covalent bonds

• the presence of strong covalent bonds make polymers unreactive and chemically inert, hence they are usually non-biodegradable

• when non-biodegradable polymers such as plastics are thrown at landfills, they cause landfills to fill up quickly as decomposers are unable to break them down

• polymers also release carbon dioxide, which is a greenhouse gas when they are decomposed via combustion. this can lead to climate change

• polymers which contain chlorine such as PVC releases toxic hydrogen chloride when burned. if polymers are incinerated by incomplete combustion, carbon monoxide may be released which is harmful to the respiratory system

advantages of recycling polymers

• reuse waste materials - better for enviroment than burning them or putting them in landfills

• saves crude oil (a finite resource)

• more economically viable instead of making more polymers

disadvantages of recycling polymers

• difficult and expensive to first seperate the different polymers (they need to be sorted into types)

what is DNA

• DNA is a polymer made from 4 different monomers called nucleotides

what is starch

• starch is a polymer based on sugars

what are proteins

• proteins are polymers based on amino acids

formulae of the first four molecules of alcohols

• alcohols contain the functional group -OH

• the first 4 members of the series are methanol, ethanol, propanol and butanol

• methanol = CH₃OH

• ethanol = CH₃CH₂OH

• propanol = CH₃CH₂CH₂OH

• butanol = CH₃CH₂CH₂CH₂OH

​ ​ Core​ ​ Practical:​ ​ Investigate​ ​ the​ ​ temperature​ ​ rise produced​ ​ in​ ​ a​ ​ known​ ​ mass​ ​ of​ ​ water​ ​ by​ ​ the​ ​ combustion​ ​ of the​ ​ alcohols​ ​ ethanol,​ ​ propanol,​ ​ butanol,​ ​ and​ ​ pentanol

method

1. use a stand, boss and clamp to secure a steel or copper can over a spirit burner. adjust the height of the can so that the lid of the burner can be removed and replaced safely

2. measure and record the mass of a spirit burner with its lid

3. use a measuring cylinder to add 100cm³ of cold water to the can. measure and record its temperature

4. place the spirit burner underneath the can. remove the lid and light the wick

5. stir the water carefully with the themometer. when the temperature has increased by about 20°C, replace the lid to put the flame out

6. measure and record the mass of the spirit burner with its lid, and the maximum temperature of the water

7. repeat steps 2-6 with different alcohols, starting with fresh water each time

analysis

the change in mass is equal to the mass of fuel burned

for each experiment, calculate the change in temperature and the change in mass

• you should find that the temperature is raised more as the chain length of the alcohols increases, because the combustion of longer chain alcohols releases more energy

recall the formulae of molecules of the carboxylic acids

• ethanoic acid is a member of the carboxylic acids, they have the functional group -COOH

• first four members are: methanoic acid, ethanoic acid, propanoic acid and butanoic acid

• methanoic acid = CHOOH

• ethanoic acid = CH₃COOH

• propanoic acid = CH₃CH₂COOH

• butanoic acid = CH₃CH₂CH₂COOH

what is formed when ethanol is oxidised

• ethanol can be oxidised to form ethanoic acid

• any alcohol can be oxidised to produce a carboxylic acid (eg. propanol → propanoic acid)

what is similar about members of a given homologous series

• have similar reactions because their molecules contain the same functional group and use this to predict the products of other members of these series

describe the production of ethanol

• ethanol can be produced by fermentation with yeast, using renewable sources

• it is produced from carbohydrates (can be sugars from fruit or starch)

• mixture must be kept warm and under anaerobic conditions (warm - so reaction is fast enough but yeast doesn’t denature. anaerobic - only carbon dioxide and water would be produced if not)

• glucose → ethanol + carbon dioxide

• C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

explain how to obtain a concentrated solution of ethanol by fractional distillation of the fermentation mixture

• ethanol concentration is about 15% from fermentation, ethanol is seperated from the reaction mixture using fractional distillation

  • water and ethanol solution are heated

  • ethanol evaporates first (has a lower boiling point than water), cools, then condenses

  • water left evaporates, cools, then condenses

compare the size of nanoparticles with the size of atoms and molecules

• nanoparticles are 1-100 nanometres across

• they contain a few hundred atoms

• nanoparticles, are smaller than fine particels, which have diameters between 100 and 2500nm (1 × 10^-7m and 2.5 × 10^-6m)

• as the side of cube decreases by a factor of 10, the surface area to volume ratio increases by a factor of 10

describe how the properties of nanoparticulate materials are related to their uses

• nanoparticles involve fullerenes

• a nanoparticle has different properties to the ‘bulk’ chemical it’s made from, because of their high surface area to volume ratio. it may also mean that smaller quantities are needed to be effective than for materials with normal particle sizes eg. fullerenes have different properties to big lumps of carbon

• they have high surface area to volume ratio, and therefore would make good catalysts

• they can also be used to produce highly selective sensors

• nanotubes could make stronger, lighter building materials

• new cosmetics, eg. sun tan cream and deodorant. they make no white marks

• lubricant coatings, as they reduce friction. these can be used for artificial joints and gears

• nanotubes conduct electricity, so can be used in small electrical circuits for computers

explain the possible risks associated with some nanoparticulate materials

• some worries that they may be harmful to health - ie. enter bloodstream and cause harm

• a lot of effects of nanoparticulate materials are unknown and this is worrying for some people as risks are not fully known

physical properties of glass ceramics in comparison to uses

properties: transparent, hard, brittle, poor heat and electrical conductors

uses: windows, bottles

physical properties of clay ceramics in comparison to uses

properties: opaque, hard, brittle, poor heat and electrical conductors

uses: bricks and porcelain

physical properties of polymers in comparison to uses

properties: can be made transparent/translucent/opaque, poor heat and electrical conductors, can be tough or ductile

uses: plastic bags, bottles

physical properties of metals in comparison to uses

properties: shiny, good heat and electrical conductors, hard, tough

uses: cars, bridges, electrical cables