- additives improves food:
- food colour- look more appetising
- flavour enhancer - bring out taste, smell without adding taste of own
- antioxidants - preserve food
- emulsifiers - help oil and water blend (e.g. salad cream, ice cream, mayonnaise)
- oil and water naturally separate
- emulsions - made up of droplets of a liquid suspended in another liquid
- emulsifiers are molecules with one part attracted to water and the other oil or fat
- hydrophillic - bonds to water molecules
- hydrophobic - bonds to oil molecules
- when shaken, oil forms droplets surrounded by bits of emulsifier with the hydrophillic end facing outwards.
- other oil droplets are repelled by hydrophillic end while water bonds so it wont separate
- cooking - better taste/texture, easier to digest, kill off microbes(important in meat), some foods are poisonous when raw (red kidney beans contain poison)
- chemical change - new substance is made, irreversible change, energy change occurs
- Eggs and Meat (good source of protein)
- energy from cooking breaks chemical bonds in protein allowing them to change shape.
- gives more edible texure
- change is irreversible (called denaturing)
- surrounded by rigid cell wall made of cellulose (humans cannot digest)
- cooking ruptures cell walls and starch grains inside swell up and spread out
- makes it softer and flexible and easier to digest
- Baking Powder
- added to cakes to make them rise
- contains sodium hydrogencarbonate which breaks down to make carbon dioxide
- sodium hydrogencarbonate(Na2CO3)→ sodium carbonate(NaHCO3) + carbon dioxide+water
- called thermal decompositon as Na2CObreaks down
- carbon dioxide test - turns limewater cloudy when bubbled through
some are natural others are artificial. perfumes need certain properties:
- evaporates easily - must reach nose easily
- non-toxic - cannot posion user
- no reaction to water - so no reaction with sweat
- non-irritant - could not be used if causes harm
- insoluble in water - not washed away easily
- to evaporate the forces of attraction must be overcome to change state. they need more energy for this, which is why they evaporate faster when heated.
- perfumes evaporate easily (very volatile) as the attraction between their mollecules are very weak and easily overcome.
- esters are used in perfumes as they have pleasant smells.
- found naturally in fruit but can be made in the lab also (esterification)
- alcohol + acid → ester + water
Nail Varnish, Testing and Solution
- solution - mixture of solute and a solvent that does not separate
- solute - substance being dissolved
- solvent - liquid its dissolving in
- soluble - it can dissolve
- insoluble - it cannot dissolve (e.g. precipitate)
- solubility - measure of how much it will dissolve
nail varnish is insoluble in water as the attraction between the particles in nail varnish and water molecules are weaker then the attraction between themselves. This means they do not form a solution. But it does dissolve in acetone (propanone / nail varnish remover) as the attraction between acetone and nail varnish is stronger then attraction between themselves.
- Testing cosmetics - ensure safety. but some tests are carried out on animals with is contraversial
- OK - to check they wont damage humans
- BAD - wrong to cause suffering just to test cosmetics, especially when results could be inconclusive
- banned in the EU because of concerns for animal welfare
Paints and Pigments
- pigment - gives paint its colour
- binding medium - sticks pigments to surface being painted
- solvent - thins the paint to more spreadable
- emusion paints (water based) - water solvent evapourates so paint dries leaving behind binder and pigent as a thin solid film
- fast drying and dont produce harmful fumes - ideal for indoors
- Oil Paints - oil based solvent evapourates as paint dries. then oil is oxidised by oxygen in air before forming tough layer on surface
- glossy, waterproof, hardwearing but produce harmful fumes - ideal outdoors
Colloid - type of mixture where one substance is spread or dispersed evenly in another substance but not dissolved
- paints are colloids - solid particles are mixed and dispersed with particles of liquid. the "solvent" they contain are there to spread paint thinly rather then to dissolve it
- do not separate or settle to the bottom as they are too small to settle.
Thermochromic - colour change by temperature
- change colour when heated or cooled.
- liquid crystals (used in calculator displays) are thermochromic making them good for thermometers and mood rings (change colour according to body temp)
- heat sensitive dyes - colourless at one temp and become coloured at another temp.
- good for mugs or kettles to warn when hot.
- babies spoons and bath toys to warn parents if too hot
- can be mixed with acrylic paints to give even more colour changes.
Phosphorescent pigments - glow in the dark
- in the light they absorb light energy which they release as light over a period of time. stop after released all stored energy. - good for warning signs and clock faces
- radioactive paints used to make glow in the dark pains (radium or tritium)
- radiation can damabe cells and may cause cancer - modern phosphorescent pigments are not radioactive and are much safer
Alkanes and Alkenes
- Hydrocarbons only contain hydrogen and carbon atoms
- held together by covalent bonds - very strong, formed when atoms share electrons
Alkanes have C-C bond
- saturated compounds - only has a single covalent bond between carbon atoms
- wont decolourise the bromine water (addition reaction used to test for unsaturation)
- wont form polymers (no double bonds to open)
Alkene have C=C bonds
- unsaturated compounds - has at least one doube covalent bond
- double bond can open up and join onto things, making them more reactive (e.g. polymerisation)
- turns bromine water from an orange to a colourless dibromo solution (decolourised)
- made when small molecules (monomers) join end to end to make large molecules
- high temperature, unsaturated monomers and pressure needed for polymerisation to happen
- involves unsaturated alkene monomers reacting together to make a saturated polymer molecule
- displayed formula - draw the monomer but change double bond to single, draw two bonds either side where the double bond was, put brackets round the molecule passing through outer bonds.
- long chains held together by weak intermolecular forces
- chains slide over eachother
- stretched easily and low melting point
- strong bonds between polymer chains - cross linking bridges or covalent bonds between chains
- high melting points, rigid and cannot be stretched
- crosslinks hold it firmly together
- waterproof - stops water getting in but stops sweat getting out
- breathable - stops water getting in and lets sweat out
- Nylon is a polymer. it is waterproof, tough, lightweight and blocks UV light but does not let water vapour through, so sweat condenses making you feel uncomfortable.
- Gore-Tex® - has the same properties but it is breathable by having different layers
- polyurethane (PTFE) positioned between outer and inner lining- has tiny holes too small to let water droplets in, but big enough to let water vapour out. this is why rain cant get in and sweat can get out.
- this is fragile so is laminated with nylon
- Non-biodegradable plastics means they dont rot as not broken down by micro-organisms.
- landfil - still there years later, fill up quickly, waste of land, waste of plastic
- burnt - sulfur dioxide and posionous hydrogen chloride/cyanide let out and a waste of plastic
- resuse then recycle - no waste but have to sort for recycling which is expensive and difficult as must be done by hand
- biodegradable polymers - get wet, break down starch causing to crumble
- dissolvable polymers - dissolve in water
crude oil is a fossil fuel. it is formed from living things that lived in the sea millions of years ago. it is a non-renewable resource, we are using it much faster then it can be made all fossil fuels are a finite resource - they will run out if we continue to use them crude oil can be separated into different hydrocarbons by fractional distillation. in a fractioning column, the hydrocarbons are separated by boiling points. --------------- the large the hydrocarbon molecules, the stronger the intermolecular forces. they have a high boiling point as more energy is needed to break these bonds
Making Crude Oil More Useful
- crude oil forms on the seabed where rock forms over it, then the oil is forced up through the rock. Oil companies can use oil wells to drill down through the impermeable rocks to get it out.
- oil tanker crash - oil slick - oil covers bird feathers, so they cannot fly and they die of cold as stops them from being waterproof - detergents can be used to break them up, but these are also harmful to environment
- countries with most oil will have the power over other countries which could cause political conflicts - USA/UK have to depend on politically unstable countries for supplies and could be cut off at any time.
- splits up longer chained hydrocarbons that are in less demand to shorter chained molecules in higher demand as the supply is less then the long-chain hydrocarbons.
- helps match supply of fractions to the demand for them creating more widely used fractions
- involves heating oil fractions to a high temperature and passing them over a catalyst (aluminium oxide)
- produces an alkene and alkane
- complete combustion - plenty of oxygen available
- the carbon oxidises to carbon dioxide
- the hydrogen oxidises to water (remember that water, H2O, is an oxide of hydrogen).
- clean blue flameit does not matter which hydrocarbon fuel is burned completely with O2, water and carbon dioxide will be produced
- hydrocarbon + oxygen → carbon dioxide + water
- you can show a fuel burns to give CO2 and H2O
- water pump draws gas from burning hydrocarbon, water collects inside cooled U-tube.
- show its water by checking boiling point
- limewater turns milky showing that CO2 is present
- if there isnt enough oxygen, the combustion will be incomplete
- this gives carbon monoxide and carbon as waste products
- yellow smokey flame
- hydrocarbon + oxygen --> carbon monoxide + carbon + water
- carbon monoxide is colourless, odourless and poisonous gas and is very dangerous
- Gas fires and boilers must be serviced regularly to ensure they do not produce carbon monoxide.
- hydrocarbon + oxygen --> carbon monoxide + carbon + water
Composition of Air
The Earth's atmosphere has remained much the same for the past 200 million years.
Evolution of the Atmosphere
- phase 1 - Volcanoes gave out steam and CO2
- originally molten
- cooled and thin crust formed
- volcanoes kept erupting releasing gases inside Earth, "degassing"
- early atomsphere mostly CO2 and water vapour, later condensing to form ocean
- phase 2 - green plants evolved and produced O2
- CO2 dissolved in oceans
- plants photosynthesised removing CO2 and producing O2
- O2 levels increase and CO2 locked up in fossil fuels and sedimentary rocks
- N2 made by ammonia reacting with O2 and released by denitirfying bacteria
- phase 3 - ozone layer allows evolution of complex animals
- build up of O2 killed animals that could not tolerate it
- allowed evolution of complex organisms that used O2
- O2 created ozone layer blocking harmful rays from sun
- virtually no CO2 left
Humans and Air
- population increasing means more CO2 in atmosphere
- so more respiration giving out more CO2
- more energy needed for lighting/cooking/transport
- industialised - increasing energy demand per person (more electrical goods etc)
- more land needed for houses
- deforestation = less plants to take in CO2
build up of pollutants make life unhealthy and miserable
- number of respiratory illness has increased - especially among young people
- Carbon monoxide
- incomplete combustion of fuel in car engines
- poisonous gas
- fainting, coma, death
- Oxides of nitrogen
- formed from heat and pressues in car engine
- oxides of nitrogen react with other pollutants in sunlight to get ozone (photochemical smog)
- leads to breathing difficulties, headaches, tiredness
- sulfur dioxide
- sulfur impurities in the fuel burn
- oxides of nitrogen and sulfur dioxide react to form acid rain
- killing plants and aquatic life
- eroding stonework
- corroding metals
- Catalytic converters convert carbon monoxide into carbon dioxide (mixture of platinum and rhodium so expensive)
- carbon monoxide + nitrogen oxide --> nitrogen + carbon dioxide