GCSE core chemistry revision 2

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PLANT OILS

EXTRACTING VEGETABLE OIL

plants turn glucose into other chemicals using more chemical reactions- vegetable oils from plants, such as oilseed rape, make biofuels and foodstuffs

find oils in the seeds- farmers collect the seeds from plants using a combine harvester, seeds then taken to a factory where they are crushed and pressed to extract their oil, impurities then removed and it is processed to make useful products

extract other vegetable oils using steam- distillation, oil and water evaporate together and are collected by condensing them- then water and impurities removed

all vegetable oils are hydrocarbon chains

can detect double bonds in unsaturated oils with bromine water

vegetable oils provide nutrients and have a high energy content, they are important foods and can be used to make biofuels

COOKING WITH VEGETABLE OILS

boiling point of vegetable oil is higher than water, so can be used at a higher temperature

in oil, food cooks more quickly, outside of the food turns a different colour and becomes crispier, inside of food softer

cooking food in oil also means that the food absorbs some of the oil. Oil contains a lot of energy so energy content of fried food much higher than food cooked in water (why unhealthy)

hardening unsaturated vegetable oils- react oil with H2 gas at 60 degrees with a nickel catalyst- replaces double bonds for single bonds- makes hydrogenated oils that are solids at room temp (use to make spreads for bread or to make cakes)

EVERYDAY EMULSIONS

smooth foods made of oil and water- make oil into droplets then these spread throughout the water and produce a mixtuer called an emulsion - eg milk

in mayonnaise- eggs work as an emulsifier- make sure that the oil and water can't separate and emulsion stays thick and smooth

popular emulsion is ice cream- emulsifiers keep the oil and water together while the ice cream is freezed (so water won't freeze separately producing crystals of ice)

emulsifiers also important in the cosmetics industry

emulsifier has a hydrophobic tail and hydrophilic head- tails dissolve in oil making tiny droplets, the surface of each oil droplet is charged by the heads sticking out the water. As like charges repel, the oil droplets repel each other, keeping them spread throughout the water (emulsified)

FOOD ISSUES

food additive = a substance added to food to preserve it or to improve its taste,texture or appearance.

Additives approved for use in Europe = E numbers, each group of additives is given a E number (E4 = emulsifiers, stabilisers and thickeners)

emulsifiers make it less obvious that foods are rich in oil and fat (eg chocolate)- more edible and nicer to eat

benefits of eating vegetable oils- as oppose to animal fats, better for the heart, source of nutrients such as vitamin E, help keep arteries clear and reduce chance of heart disease, lower level of bad cholesterol

OUR CHANGING PLANET

STRUCTURE OF THE EARTH

dense core, surrounded by a mantle, and outside the mantle there is a thin outer layer called the crust, above the earth's crust we have a thin layer of gases called the atmosphere

core- half the radius- inner is solid outer is liquid, made of nickel and iron

mantle- behaves like a solid, but is able to flow very slowly

all minerals we depend on come from the crust of the Earth, oceans and the atmosphere- non-renewable

THE RESTLESS EARTH

continents were once joined together as one land mass (evidence in edges of continents, fossils and layers of rock built up in the same sequence

continents moving at a rate of a few cm a year, earth's crust and uppermost part of the mantle is split into tectonic plates. Deep within the earth, radioactive atoms decay, producing energy which heat up molten minerals in the mantle which expand. They become less dense and rise towards the surface then cooler material sinks to take their place. Forces created by these convection currents move the tectonic plates

Where the boundaries of the plated meet, huge stresses build up, these forces make the plates buckle and deform and mountains may be formed. May slip past one another causing earthquakes

difficult to predict accurately when and where earthquakes will happen

EARTH'S ATMOSPHERE IN THE PAST

4.5 billion years ago formed

several theories- one that volcanoes released CO2, water and nitrogen gas- forming the early atmosphere

Water vapour in the atmosphere condensed as Earth cooled and fell as rain (oceans formed)

earth began to stabilise, atmosphere made mainly of CO2 (some water vapour and traces of methane and ammonia)- like atmospheres of Mars and Venus, some scientists think nitrogen present too

Bacteria and algae evolved as well as plants, removed CO2 and made O2- atmosphere becam richer and richer in oxygen- animals could then evolve

LIFE ON EARTH

Where did living things come from? many theories, best are the ones that explain most of the widely accepted evidence

Miler-Urey experiment- made amino acids using a model of the early atmosphere (water, ammonia, methane and hydrogen) and a high voltage spark to represent lightning

Another theory based on analysis of meteors- Murchison meteorite- rich in organic molecules

another source of biological materials from oceans near volcanic vents

organic materials could have formed a primordial soup- react together somehow to make the first primitive cells

GASES IN THE ATMOSPHERE

carbon dioxide- only 0.04% in today's atmosphere, because it has gone into living organisms and locked into rock

CO2 taken up by plants in photosynthesis- animals eat and transferred to animal tissues, dead bodies of these build up at the bottom of large oceans- form sedimentary rocks like limestone, some crushed by movements in the Earth and formed fossil fuels

CO2 also dissolved in oceans, reacted and made insoluble carbonate compounds (fell to seabed and helped to form more carbonate rocks

at same time, ammonia and methane reacted with O2 in the air and it was got rid of (formed CO2 and water, N2 and water). Nitrogen levels built up as this is a very unreactive gas

gases separated by fractional distillation of liquid air

air cooled to a temp below -200 degrees so condenses into a liquid- pressure released- CO2 and water removed as they are solids at this temp

nitrogen boils off first and is collected at the top of the column

uses of nitrogen- cool things down, store things, unreactive so used in sealed packaging to stop food going off, used on oil tankers to reduce the risk of explosion, used to make ammonia

uses of oxygen- medical and to help things react

CARBON DIOXIDE IN THE ATMOSPHERE

plants and oceans are CO2 sinks

oceans act as a buffer to increases in CO2 in the atmosphere- react more to make insoluble carbonates that are deposited at the bottom of the ocean and soluble hydrogencarbonates that remain dissolved in sewater

however now signs that the seas can't cope with all the additional CO2

plant oils

our changing planet