MODULE C1- CARBON CHEMISTRY

POLYMERS' PROPERTIES DECIDE WHAT THEY'RE USED FOR:

• Strong, rigid polymers such as high density polyethene are used to make plastic milk bottles.
• Light, stretchable polymers such as low density polyethen are used for plastic bag- it has a low melting point
• PVC is strong and durable, it can be made either rigid or stretchy,rigid kind is used to make window frames and piping- the stretchy kind is used to make synthetic leather
• Polystyrene foam is used in packaging to protect breakable things, and it's used to make disposable cups (the trapped air in the foam makes it a good thermal insulator)

POLYMERS ARE OFTEN USED TO MAKE CLOTHES:

• Nylon is a synthetic polymer- fabrics made from this are not waterproof but can be coated with polyurethene to make tough, hard-wearing and waterproof outdoor clothing which also keeps UV light out.
• It doesn't let water vapour pass through it, sweat condenses inside- material is not breathable.
• GORE-TEX is breathable whilst being waterproof.
  • Made by laminating a thin film of a plastic called expanded PTFE onto a layer of another fabric, such as polyester or nylon- this makes PTFE sturdier
  • PTFE has tiny holes- water vapour goes through-breathable- PTFE repels liquid water- big water droplets can't go through

NON-BIODEGRADABLE PLASTICS CAUSE DISPOSAL PROBLEMS:

• Most polymers can't be broken down by micro organisms and so they can't rot
• Landfill sites fill up quickly, and they're a waste of land and a waste of plastic.
• When plastics are burnt, some of them release gases such as acidic sulfur dioxide and poisonous hydrogen chloride and hydrogen cyanide.
• The best thing is to re-use plastic as many times as possible and then recycle them if you can.
  • However, sorting out plastic for recycling can be expensive.
• Chemists are working on a variety of ideas to produce polymers that biodegrade or dissolve-that way any plastic that is thrown away breaks down or dissolves rather than sitting there in landfill for ages.

HYDROCARBONS CONTAIN ONLY HYDROGEN AND CARBON ATOMS ONLY:

• A hydrocarbon is any compound that is formed from carbon and hydrogen atoms only.
• They are useful chemicals

COVALENT BONDS HOLD ATOMS IN A MOLECULE TOGETHER:

• All the atoms in hydrocarbon molecules are held together by covalent bonds. These covalent bonds are very strong. They form when atoms 'share' electrons.
• This way both atoms gain a full outer shell- each covalent bond provides one extra shared electron for each atom.
• So carbon atoms always want to make a total of 4 bonds while hydrogen atoms only want to make 1

ALKANES HAVE ALL C-C SINGLE BONDS:

• Alkanes are the simplest type of hydrocarbon- they're chains of carbon atoms with 2 or 3 hydrogen atoms attached to each one.
• Alkanes are saturated compounds- they contain only single covalent bonds between their carbon atoms.
• Difference between alkane and alkene: add bromine water ( alkene becomes colourless)
• Alkanes won't form polymers- no double bonds to open up
• Alkanes- CnH2n+2

COVALENT BONDS CAN BE SINGLE OR DOUBLE BONDS:

• A single covalent bond is formed when 2 atoms share a pair of electrons
• To form a double bond, 2 atoms will 2 pairs of electrons instead of just one pair
• Carbon atoms can do this-each bond still provides 1 extra shared electron for each atom, but there 2 bonds between the carbons

ALKENES HAVE A C=C DOUBLE BOND:

• Alkenes are hydrocarbons with 1 or more double bonds between carbon atoms
• They're unsaturated compounds. An unsaturated compound is just one that contains at least 1 double covalent bond.
• Their double bonds can open up and join onto things-- this makes alkenes more reactive- they can form long polymer chains as they open up
• CnH2n

ALKENES REACT WITH BROMINE WATER:

• It's really reactive so it joins with double bonds- it becomes decolourised
• Saturated compound- No reaction, stays bright orange
• An addition reaction takes place if its unsaturated compound- Colourless dibromo compound formed

CRUDE OIL IS SEPARATED INTO DIFFERENT HYDROCARBON FRACTIONS:

• It's formed from the buried remains of plants and animal- over millions of years with high temp and pressure, the remains turn to crude oil which can be drilled up
• Crude oil is a mixture of lots of different hydrocarbons
• The different compounds in crude oil are separated by fractional distillation. The oil is heated until most of it has turned into gas.
• The longer hydrocarbons have high boiling points- they turn back into liquids and drain out of the coloumn early on, when they're near the bottom. The shorter hydrocarbons have lower boiling points- They drain out much later near to the top of the coloumn where it's cooler

HYDROCARBON PROPERTIES CHANGE AS THE CHAIN GETS LONGER:

• The BOILING POINT increases.
• Less flammable
• More viscous
• Less volatile

You can separate out the random mixture of all kinds of hydrocarbons that have similar chain lengths and so similar properties.

ITS ALL DOWN TO THE BONDS IN AND BETWEEN HYDROCARBONS:

• The STRONG COVALENT BONDS between the carbons and hydrogens within each hydrocarbon molecule.
• The INTERMOLECULAR FORCES OF ATTRACTION between different hydrocarbon molecules.
• When the crude oil mixture is heated, the molecules are supplied with extra energy.
• The molecules move about more- eventually a molecule will have enough energy to overcome the intermolecular forces- it whizzes off as a gas.
• Covalent bonds can't break as the bond is stronger than the IMF
• The IMF of attraction break a lot more easily in small molecules than they do in bigger molecules- they are much stronger between big molecules than small molecules.

CRACKING IS SPLITTING UP LONG-CHAIN HYDROCARBONS:

• Cracking turns long alkane molecules into smaller alkane and alkene molecules.
• It's a form of THERMAL DECOMPOSITION- breaking down of a substance through heat- to break the covalent bonds lots of heat and catalyst needed.
• A lot of the longer molecules produced from fractional distillation are cracked into smaller ones because there's MORE DEMAND for products like petrol and kerosene.
• Cracking also produces alkenes which is used for polymers.

CONDITIONS NEEDED FOR CRACKING: HOT, PLUS A CATALYST:

• Vaporised hydrocarbons are passed over powdered catalyst at 400-700 degrees.
• Aluminium oxide is the catalyst- long chain molecules split apart on the surface of the bits of catalyst.
• LONG CHAIN HYDROCARBON MOLECULE = SHORTER ALKANE MOLECULE + ALKENE

IT WILL RUN OUT EVENTUALLY..

• Crude oil supplies are limited and non-renewable. New reserves are sometimes found and new technology means we can get to oil that was once too difficult to extract.
• Alternative energy sources: nuclear, wind power, ethanol to power cars

OIL CAN CAUSE POLITICAL AND ENVIRONMETAL PROBLEMS:

POLITICAL:

• 1) price of oil rises and fuels get more expensive.
• 2) The countries with the most oil and natural gas will have power over other countries- wars can be caused
• 3) It'll get harder for countries without oil and gas to get hold of it- we have to depend on politically unstable countries- likely chance of being cut off.

ENVIRONMENTAL:

• 1) Oil tanker crashes - big oil slicks
• 2) Oil covers sea bird's feathers and stops them being waterproof- die of cold.
• 3) Detergents are used to clean up oil slicks- this harms the wildlife and can be toxic.

THERE'S A LOT TO CONSIDER WHEN CHOOSING THE BEST FUEL:

1) Energy value

2) Availability

3) Storage- if it's flammable then you have to store it carefully

4) Cost

5) Toxicity- some can produce poisonous fumes

6) Ease of use- whether it lights easily

7) Pollution

COMPLETE COMBUSTION HAPPENS WHEN THERE'S PLENTY OF OXYGEN:

Hydrocarbon + oxygen = carbon dioxide + water (+ energy)

• It releases lots of energy and only produces those two harmless waste products
• The gas burns with a clean blue flame

CH4 + 2O2 = 2H2O + CO2 (+ energy)

• The water pump draws gases from the burning hexane through the apparatus.
• Water collects inside the coolued U-tube and you can show that it's water by checking its boiling point.
• The limewater turns milky, showing that carbon dioxide is present

INCOMPLETE COMBUSTION OF HYDROCARBONS IS NOT SAFE:

• If there isn't enough oxygen the combustion will be incomplete. This gives carbon monoxide and carbon as waste products, and produces a smoky yellow flame.

Hydrocarbon + oxygen = carbon dioxide+ water + carbon monoxide + carbon +(energy)

• The carbon monoxide is colourless, odourless and poisonous gas and it's very dangerous.
• The black carbon given off produces sooty marks
• You want lots of oxygen when you're burning fuel - you get more heat energy given out

4CH4 + 602 = C + 2CO + CO2 + 8H2O (+energy)

PHASE 1-  VOLCANOES GAVE OUT STEAM AND CO2:

• The Earth's surface was originally molten for million of years.
• It cooled and a thin crust formed, but volcanoes kept erupting which released gases from inside. 
• The early atmosphere was mostly CO2 and water vapour 

PHASE 2- GREEN PLANTS EVOLVED AND PRODUCED OXYGEN:

• CO2 dissolved in the oceans.
• Green plants evolved over most of the Earth- as they photosynthesise they removed CO2 and produced O2
• Much of the CO2 eventually got locked up in fossil fuels and sedimentary rocks.
• N2 was put into the atmosphere through ammonia reacting with oxygen, and was released by denitrifying bacteria.
• N2 is not reactive and doesn't break down

PHASE 3- OZONE LAYER ALLOWS EVOLUTION OF COMPLEX ANIMALS:

• The build up of oxygen killed off early organisms.
• Allowed the evolution of more complex organisms.
• The oxygen created the ozone layer to block of harmful rays from the sun

CARBON IS CONSTANTLY BEING RECYCLED:- Carbon exists in the atmosphere as carbon dioxide gas

1. Carbon enters the atmosphere as carbon dioxide from respiration and combustion.
2. Carbon dioxide is absorbed by producers to make carbohydrates in photosynthesis.
3. Animals feed on the plant passing the carbon compounds along the food chain. Most of the carbon they consume is exhaled as carbon dioxide formed during respiration. The animals and plants eventually die.
4. The dead organisms are eaten by decomposers and the carbon in their bodies is returned to the atmosphere as carbon dioxide. In some conditions decomposition is blocked. The plant and animal material may then be available as fossil fuel in the future for combustion.

 HUMAN ACTIVITY AFFECTS THE COMPOSITION OF AIR:

• More people= more energy needed for lighting, heating, cooking
• Lifestyles are changing- more countries becoming industralised
• Energy demand per person is increasing
• More people= more land for food and housing- cutting trees for this- deforestation- trees take in CO2 out of the atmosphere and now they can't do this.

ACID RAIN IS CAUSED BY SULFUR DIOXIDE AND OXIDES OF NITROGEN:

• When fossil fuels are burned they release sulfur dioxide and nitrogen oxides
• When the gases mix with clouds they form dilute sulfuric acid and dilute nitric acid
• This fallas acid rain

ACID RAIN KILLS FISH, TREES AND STATURS

• Acid rain causes lakes to become acidic and many plants and animals die as a result.
• Acid rain kills trees and damages limestone buildings and ruins stone statues. It also makes metal corrode.

OXIDES OF NITROGEN ALSO CAUSE PHOTOCHEMICAL SMOG: It is caused by sunlight acting on oxides of nitrogen. These oxide combine with oxygen in the air to produce ozone

CARBON MONOXIDE IS A POISONOUS GAS: It can stop your blood doing its proper job of carrying oxygen. It is formed form incompelte combustion.

IT'S IMPORTANT THAT ATMOSPHERIC POLLUTION IS CONTROLLED: Asthma levels have increased. Catalytic converters on motor vehicles reduce the amount of CO and Nitrogen oxides getting into the atmosphere. Catalyst is platinum and rhodium.

Carbon monoxide (2CO) +Nitrogen oxide(2NO) =Nitrogen (N2) +Carbon Dioxide (2CO2)