GCSE chemistry - unit 1 - making polymers and polymerisation

Making Polymers and Polymerisation

ALKENES

• Double bond
• Gas
• Very flammable so could be used as a fuel BUT...
• They can join their individual molecules (MONOMERS) together to make POLYMERS
• This makes plastic which is much more useful

The bracket and n just means that depending on how many monomers you get, the size of the polymer will vary. YOU WILL ALWAYS GET THE SAME NUMBER OF CARBONS AND HYDROGENS THEY WILL JUST BE JOINED WHEN THE DOUBLE BOND BREAKS.

Polymers (plastics)

• Very useful
• Lots and lots of uses (packaging etc.)
• Taken to landfill and can't decompose because they're very unreactive (this is bad)
• Scientists are working on biodegradable polymers by adding corn starch which bacteria can feed off and break down
• These new cornstarch polymers will reduce that amount of pollution caused by polymers
• Polymers can also be re-used to cause less harm to the environment

Uses for polymers

• Food packaging - can let carbon dioxide out and oxygen in
• Fabric coating (protective layer)
• Breathable fabrics like vortex with let's out sweat and keeps out rain
• HYDROGELS - absorbs a lot of moisture so good for wounds
• SHAPE MEMORY POLYMERS, when heated, go back to their original shapes (good for glasses, car bumper etc.)

GCSE chemistry - unit 1 - cracking alkanes to make alkenes

Cracking alkanes to make alkenes

Short chain hydrocarbons (alkanes) are very useful. Especially for fuels.

Long chain hydrocarbons (alkanes) aren't as useful.

WE CRACK A LONG ALKANE TO MAKE A SHORTER ALKANE AND AN ALKENE

The wool is soaked in paraffin (made up of long hydrocarbons/alkanes). This evaporates at the start and when it meets the porcelain bits (the catalyst) it THERMALLY DECOMPOSES (breaks down chemically because of heat). The product is a gas made up of a shorter ALKANE and an ALKENE, seen below:

The shorter hydrocarbon is much more useful as it has a higher flammability and can now be added to petrol.

The ALKENE contains a double bond therefore it's UNSATURATED

The test for unsaturated (ALKENE) hydrocarbons

Bromine water turns colourless when it meets unsaturated hydrocarbons but stays orange when it meets saturated hydrocarbons (without double bonds - alkanes)

GCSE chemistry - unit 1 - burning hydrocarbon fuels

Burning Hydrocarbon Fuels

NEEDED FOR: 

• Transport
• Electricity
• Heating

BAD BECAUSE:

• Sulfur dioxide is created and contributes to acid rain
• Nitrogen from the air reacts and also causes acid rain
• Soot are tiny fragments of carbon that reduce the amount of light that reaches earth (GLOBAL DIMMING)
• When burnt, carbon becomes oxidised to make carbon dioxide which leads to global warming
• INCOMPLETE COMBUSTION (not enough oxygen) leads to carbon monoxide (poisonous gas)
• Crude oil is running out
• not CARBON NEUTRAL (see below)

There is a solution however...

Biofuels (biodiesel and ethanol)

Biodiesel and ethanol are made from plant material. They are both CARBON NEUTRAL because plant pull in the carbon dioxide through photosynthesis and, when burnt, put the same amount into the air again (no more carbon is put into the air).

• Labour intensive process so provides lots of jobs
• Low technology and energy use so a lot cheaper
• Carbon neutral, renewable and sustainable
• Using a lot of land that could be used for growing food crops
• What would we do if there were massive crop failures?
• A very slow process 
• Habitat destruction to grow crops so reduction in biodiversity

ETHANOL is produced by the fermentation of sugared cane and is a fuel suitable for cars.

GCES chemistry - unit 1 - crude oil

Crude Oil

Crude oil is made up of remains of sea creatures, decomposing under the sea bed with no exposure to air and is deeply buried in rock under the sea. In the sea, pipelines supply crude oil to oil rigs which is then pumped into oil tankers which take it to be processed.

Crude oil is a thick, black and stickler liquid and is a mixture of lots of different compounds. Because it is a mixture, it is easily separated because the compounds are not chemically bonded.

Separating these compounds - FRACTIONAL DISTILATION

• The different compounds in the crude oil have different boiling points
• The compounds are called hydrocarbon molecules (made of hydrogen and carbon)
• The smallest hydrocarbons have the lowest boiling and cooling points
• The smallest are also highly flammable so are good for fuels
• The longest have low flammability and a high boiling and cooling point

In a fractionating column, crude oil vapour is pumped into the bottom where the temperature is the hottest and the larger molecules feed off as they cool at the higher temperatures. The temperature at the top is the lowest so this is where the smaller hydrocarbons condense and feed off (the thinner fuels)

Alkanes

These hydrocarbons are called ALKANES which contain NO double bonds and have a general rule for the number of carbon to hydrogen ratio... Cn H2n+2 so if you have 2 carbons you will have double that, add two = 6 hydrogens. They are SATURATED because they have no double bonds.

The first four shortest alkanes are METHANE, ETHANE, PROPANE, BUTANE.

GCSE chemistry - unit 1 - alloys

Alloys

An alloy is a mixture of two elements, one of which is a metal. Alloys often have properties that are different to the metals they contain. This makes them more useful than the pure metals alone. For example, alloys are often harder than the metal they contain.

Alloys contain atoms of different sizes, which distorts the regular arrangements of atoms. This makes it more difficult for the layers to slide over each other, so alloys are harder than the pure metal.

ALLOYS ARE NOT CHEMICALLY BONDED THEY ARE JUST MIXED 

Example

Iron is produced in a blast furnace with coke, limestone and iron oxide (from iron ore) in it. The coke contains carbon which takes the oxygen away from the iron oxide to leave just iron. This is called REDUCTION (loss of oxygen)

The iron produced is called impure pig iron and has to be purified to make it stronger.

Scientist can also control the amount of carbon they put in it to form STEEL.

LOW CARBON STEEL has 0.4% carbon and is easy to shape and not as brittle (easily broken) 

HIGH CARBON STEEL has 1.5% carbon and is resistant to corrosion, is harder but is more brittle

If we mix chromium with iron however we get stainless steel which does not corrode, rust or react.

Most metals are really soft in pure form and have limited use. We add copper to gold and aluminium to make them. Iron is the exception where you can add carbon to form steel.

GCSE chemistry - unit 1 - extracting metals

Extracting Metals

Metals are very useful as so many thing are made out of it. Metals are found in metal ores (rock with large amounts of the metal of interest; enough metal to make it worth while)

The metal ore contains impurities  and the actual metal is chemically combined with substances (usually oxygen).

First we CONCENTRATE the metal ore (basically get rid of any impurities) by SMELTING (heating) it.

The metal ore without impurities then under goes either DISPLACEMENT or ELECTROLYSIS to remove what it is chemically combined with; mostly oxygen)

All of this will happen only if the metal that is produced is worth more than the cost of getting it out if the ore (A HIGH GRADE ORE). If it is not worth while, they need to find a cheaper way of extraction or one that gets more of the metal out. If not, it's not worth it.

The reactivity series

Potassium              MOST REACTIVE
Sodium
Calcium
Magnesium
Aluminium
-----------------
*carbon*
-----------------
Zinc
Iron
Tin
Lead
Copper
Silver
Gold                      LEAST REACTIVE

If the metal is LESS reactive than carbon they undergo DISPLACEMENT. This means they are reacted with carbon and because the carbon is more reactive than them, it will take away the oxygen the the metal is bonded with to leave the metal and carbon dioxide. This is the cheaper of the two.

If the metal is MORE reactive than carbon they undergo ELECTROLYSIS because carbon is less reactive than theses metal so won't be able to steal the oxygen from them. Electrolysis uses electricity to separate the metal away from the oxygen.

IT IS IMPORTANT TO NOTE THAT GOLD IS SO UNREACTIVE THAT IT IS FOUND NATIVE IN THE GROUND (DOES NOT NEED TO BE EXTRACTED)

E.g. COPPER EXTRACTION

ELECTROLYSIS - a negative and positive electrode are placed in the melted ore solution (IN COPPER'S CASE IT IS CHEMICALLY BONDED WITH SULFUR NOT OXYGEN). The sulfur and copper have bonded ionically so the copper is made up of positive ions and the sulfur, negative ions. The positive copper ions are attracted to the negative electrode so is now separated and can be purified. Salt is left at the positive electrode.

DISPLACEMENT - scrap iron (more reactive than copper) removes the sulfate from the copper sulfate and the copper coats itself around the iron which can be easily removed and purified. This is a lot cheaper

The problem is, there's a shortage of high grade copper ores. We can use PHYTOMINING and BIOLEACHING  to extract copper from low grade ores (containing less than 1% copper) and then use electrolysis and displacement as usual after.

Phytomining

• Grow certain type of plant on land with low grade copper ore in it
• Plants take copper compounds into their body tissue
• Burn plants to leave ash that contains copper which can be extracted by electrolysis or displacement

Bioleaching

• Use certain bacteria to grow on the low grade copper ore to use it as a source of nutrition
• The bacteria produce a byproduct solution containing copper
• The solution goes through electrolysis or displacement to extract the copper

GCSE chemistry - unit 1 - calcium carbonate (limestone)

Calcium Carbonate (Limestone)

Uses of limestone

• Building and statues (strong and durable rock with a nice colour)
• Can be crushed, mixed with clay and heated to make cement
• Can add sand to cement to make mortar (like cement, hard and strong once set and lasts for a long time)
• If you add aggregate (small pebbles) to mortar you get concrete
• So LOTS of uses as BUILDING MATERIALS

Quarrying

• Limestone is a rock so is found in the ground and has to be quarried
• This involves using explosives and heavy mechanical equipment which creates noise dust and pollution
• It spoils the landscape + habitats
• The land is ruined so much that it can't be used again
• It produces a valuable material (limestone)
• Positive economic impact in the area
• Creates employment in the local area

Limestone cycle

Thermal decomposition (seen above)

HAPPENS TO OTHER CARBONATES (CO3)

We see above that Calcium carbonate, when heated, makes calcium oxide and it also makes carbon dioxide.

Other carbonates do exactly the same thing:

• Copper carbonate, when heated, makes copper oxide and carbon dioxide
• Zinc carbonate, when heated, make zinc oxide and carbon dioxide 
• Magnesium carbonate, when heated, makes magnesium oxide and carbon dioxide
• Etc.