Science C1

Fossil fuels are finite resources because they are no longer being made, or are being made very slow.

Fossil fuels are being used up faster than they are being made (Non-renewable resource).

Specific difficulties associated with finite nature of crude oil include:

-all the readily extracable resources will be used up in the future.

-Finding replacements.

Crude oil is a mixtue of many types of oil, which are all hydrocardons. 

A hydrocarbon is made up of molecules containing carbon and hydrogen only.

Crude oil is heated at the bottom of  fractionating column.

-Oil that doesnt boil sinks as a thick liquid to the bottom. (Bitumen). Bitumen has a very high boiling point. It exits at the bottom of the column.

-Other fractions, containing mixtures of hydrocarbons with similar boiling points, boil and their gasses rise up the column. The column is cooler at the top. Fractions with lower boiling points exit towards the top of the column.

Crude oil can be separated because the hydrocarbons in different fractions have differently sized molecules.

-The force between the molecules are intermolecular forces and are broken during boiling.

-The molecules of the liquid seperate from each other as molecules of gas.

-Large molecules, such as those of bitumen and heavy oil, have strong forces of attraction. A lot of energy is needed to break the forces between the molecules. These fractions have high boiling points.

-Smaller molecules, such as petrol, have weak attractive forces between them are easily seperated. Less energy is needed to break the forces between the molecules. These fractions have low boiling points.

Transporting oil can cause problems.

Oil slicks can damage birds feathers and cause their deaths.

Clean-up operations use detergents that can damage wildlife.

There may be political problems related to the extraction of crude oil, particularly where the UK is dependant on oil and gas from politically unstable countries. Oil-producing nations can set high prices and cause problems for the future supply of non-oil producing nations.

Because the demand for oil and its products is very high, there is a conflict between the needs for making petrochemicals and for making fuels. A fraction called naphtha is in high demand for use in medicines, plastics and dyes.

Cracking is a process that turns large alkane molecules into smaller alkane and alkene molecules.

An alkene molecule has a double bond, which makes it useful for making polymers.

Cracking also helps oil manufacturers match supply with demand for products like petrol.

A fuel is chosen because of its key features. For example, coal produces more pollution than petrol.

The amount of fossil fuels being burnt is increasing because populations are increasing.

-Governments are concerned because of the increasing carbon dioxide emissions that result when fossil fuels are burnt.

-Countries with huge populations, such as India or China, are now using more fossil fules, which adds further to gas emissions.

-Many governments have pledged to try to cut carbon dioxide emissions over the next 15-20 years. It is a global problem that cannnot be solved by one country alone.

Burning hydrocarbon fuels in plenty of air produces carbon dioxide and water.

Methane + Oxygen > Carbon dioxide + Water.

This can be shown using an experiment in the laboratory.

Complete combustion occurs when a fuel burns in plenty of oxygen.

-More energy is released during complete combustion than during incomplete combustion.

-Toxic gas (carbon monoxide) and soot (carbon) is made during incomplete combustion.

-The word equations for incomplete combustion are:

Fuel + oxgyen > carbon monoxide + water.

or

Fuel + oxygen > carbon + water.

Given the molecular formula of a hydrocarbon, balanced symbol equations can be constructed for :

-Complete combustion

CH4 + 2O2 > CO2 + 2H2O

-Or incomplete combustion

2CH4 + 3O2 > 2CO + 4H2O

Or

CH4 + O2 > C + 2H2O

Clean air is made up of 78% nitrogen, 21% oxygen and of the remaining 1%, only 0.035% is carbon dioxide.

These percentages change very little because there is a balance between the processes that use up and make both carbon dioxide and oxygen.

Some of these processes are shown in the carbon cycle.

The arrows in a diagram of a carbon cycle show the direction of movement of carbon compounds.

Over the last few centuries the percentage of carbon dioxide in the air has increased slightly due to:

-Deforestation - as more rainforests are cut down, less photosynthesis takes place.

-Increased population - as population increase, the worlds energy requirements increase.

Gases escaping from the interior of the earth formed the original atmosphere. Plants that could photosynthesise removed carbon dioxide from the atmosphere and added oxygen. Eventually the amount of oxygen reached its current level.

Gases come from the centre of the earth through volcanoes in a process called degassing. Scientists analyse the composition of these gasses to form theories about the original atmosphere.

One theory is that the atmosphere was originally rich in water vapour and carbon dioxide. This vapour condensed to form oceans and the carbon dioxide dissolved in the water. The percentage of nitrogen slowly increased and, being unreactive, little nitrogen was removed.

Over time, organisms that could photosynthesise evolved and converted carbon dioxide and water into oxygen. As the percentage of oxygen in the atmosphere increased, the percentage of carbon dioxide decreased, until todays levels were reached.

It is important to control the atmospheric pollution because of the effects it can have on peoples health, the natural environment and the built environment.

Sulfur dioxide is a pollutant that can cause difficulties for people with asthma. It can also dissolve in water to form acid rain that damges wildlife and limestone buildings.

A car fitted with a catalytic converter changes carbon monoxide into carbon dioxide.

In a catalytic converter, a reaction between nitric oxide and carbon monoxide takes place on the surface of the catalyst. The two gasses formed are natural components of air - nitrogen and carbon dioxide.

2CO + 2NO > N2 + 2CO2

A hydrocarbon is a compound of carbon and hydrogen atoms only.

-Alkanes are hydrocarbons that have single covalent bonds only.

-Alkenes are hydroccarbons that have a double covalent bond between carbon atoms. Double bonds involve two shared pairs of electrons.

Propane, C3H8, is a hydrocarbon because it has only C and H atoms. It is an alkane because all the bonds are single covalent bonds.

Propanol, C3H7OH, is not a hydrocarbon because it contains an oxygen atom.

Propene, C3H6, is a hydrocarbon because it contains only C and H atoms. It is and alkene because it has a double covalent bond between carbon atoms. Propene is also a monomer. Poly(propene) is teh polymer.

Bromine is used to test for an alkene. When orange bromine water is added to an alkene it turns colourless (decolourises).

The bromine and alkene form a new compound by an addition reaction. A di-bromo compound forms which is colourless.

A saturated compound only has a single covalent bonds between carbon atoms. Alkanes, like propane, are saturated. They has no double bond between carbon atoms.

An unsaturated compound has at least one double covalent bond between carbon atoms. Alkenes, like propene, are unsaturated. They has a C=C double bond.

Addition polymerisation is the process in which many alkene monomers react to give a polymer. This reaction needs high pressure and a catalyst.

You can recognise a polymer from its displayed formula by looking out for the following: a long chain, the pattern repeating every two carbon atoms. two brackets on the end eith extended bonds through them, an 'n' after the brackets.

This is the displayed formula of poly(ethene):

The displayed formula of:

-an addition polymer can be constructed when the displyed formula of its monomer is given.

-a monomer can be constructed when the displayed formula of its addition polymer is given.

This is the displayed formula of the ethene monomer:

During an addition polymerisation reaction a long chain is made until it is stopped. This long molecule is poly(ethene). The reaction causes the double bond in the monomer to break and each of the two carbon atoms forms a new bond.

Addition polymerisation involves the reaction of many unsaturated monomer molecules (alkenes) to form a saturated polymer.

Nylon is tough, lightweight, keeps water out, and keeps UV light out but does not not let water vapour through. This means that sweat condenses and makes the wearer wet and cold inside their jacket.

GORE-TEX has all the properties of nylon but is also made breathable.Water vapour from sweat can pass through the membrane but rainwater cannot.

GORE-TEX material is waterproof and yet breathable.

-It is made from a PTFE (polytetrafluoroethene)/polyurethane membrane.

-The holes in PTFE are too small for water to pass thorugh but are big enough for water vapour to pass through.

PTFE/polyurethane membrane is too fragile on its own and so it is laminated onto a nylon to produce a stronger fabric,

Scientists are developing new types of polymers:

-Polymers that dissolve.

-Biodegradable polymers.

Research into new polymers is important because there are environmental and economic issues with the use of existing polymers,

-Disposal of non-biodegradable polymers means landfill sights get filled quickly.

-Landfill means wasting land that could be valuable for other purposes.

-Disposal by burining waste plastics makes toxic gases.

-Disposal by burning or using landfill sites wastes that crude oil used to make polymers.

-It is difficult to sort out different polymers so recycling is difficult.

Atoms in polymers are held together by strong covalent bonds.

The properties of plastics can be related to simple models of their structues.

-Plastics that have weak intermolecular forces between polymer molecules have low melting points and can be stretched easily as the polymer molecules can slide over each other.

-Plastics that have strong forces between the polymer molecules (covalent bonds or cross-linking bridges) have high melting points, cannot be stretched are are rigid.

If the intermolecular forces between two polymer molecules are weak, the plastic can easily be stretched.

Protein molecules in eggs and meat permanently change shape when eggs and meat are cooked.

This changing of shape is called 'denaturing'.

The texture of egg or meat changes when it is cooked because the shapes of the protein molecules change permanently.

Potato is a carbohydrate which is easier to digest if it is cooked because:

-the starch grains swell up and spread out

-the cell walls rupture resulting in the loss of their rigid structure and a softer texture is produced.

Baking powder is sodium hydrogencarbonate.

When it is heated it breaks down (deecomposes) to give carbon dioxide.

The word equation for the decomposition of sodium hydrogencarbonate is:

sodium hydrogencarbonate > sodium carbonate + carbon dioxide + water.

The balanced symbol equation for the decomposition of sodium hyrogencarbonate is:

2NaHCO3 + Na2CO3 > CO2 + H2O

Emulsifiers are molecules that have a water-loving (hydrophilic) part and an oil or fat-loving (hydrophobic) part.

The oil- or the fat- loving part goes into the fat droplet.

Emulsifiers help to keep oil and water from seperating:

-The hydrophilic end bonds to the water molecules.

-The hydrophobic end bonds with the oil or fat molecules.

-The hydrophilic end is attracted to the water molecules which surround the oil, keeping them together.

Alcohols react with acids to make an 'ester' and water.

alcohol + acid > ester + water.

Esters are used to make perfumes.

An ester can be made using a simple experiment.

-The acid is added to the alcohol and heated for some time.

-The condenser stops the gas from escaping and helps to cool it down again, so that it can react more.

-The condenser allows the reaction to go on for longer.

A perfume must have certain properties. It must:

- Evaporate easily so that the perfume particles can reach the nose.

- Be non-toxic so it does not poison you.

- Not react with water so the perfume does not react with perspiration.

- Not irritae the skin so the perfume can be put directly onto the skin.

- Be insoluble in water so it cannot be washed off easily.

Solutions.

A solution is a mixture of solvent and solute that does not seperate out.

Esters can be used as solvents.

The volatility, or ease of evaporation of perfumes, can be explained in terms of kinetic theory.

-In order to evaporate, particels of a liquid need sufficient kinetic energy to overcome the forces of attraction to other molecules in the liquid.

-Only weak attractions exist between particles of the liquid perfume so it is easy to overcome these attractions as they have sufficient kinetic energy.

Water will not dissolve nail varnish.

- The attraction between the water molecules is stronger than the attraction between the water molecules and the nail varnish molecules.

- The attraction between the nail varnish molecules is stronger than the attraction between water molecules and the nail varnish molecules.

Paint is a colloid where the particles are mixed and dispersed with particles of a liquid (binding medium) but are not dissolved.

The components of a colloid will not seperate because the particles are scattered or dispersed throughout the mixture and are sufficiently small so as not to settle at the bottom.

Most paints dry because:

-Paints are applied as a thin layer.

-The solvent evaporates.

Emulsion paints are water based

paints that dry when the solvent

evaporates.

Oil paints dry because:

-The solvent evaporates.

-The oil is oxidised by atmospheric oxygen.

Thermochromic pigments change colour at different temperatures. Thermochromic pigements are used:

- As thermometres because they change colour when the temperature of the body or the temperature of a fridge rises.

- In the manufacture of some cups - the colour changes to show when they are hot.

- In electric kettles to keep users safe when boiling water.

- In babies spoons and bath toys, to warn if the spoon or toy is too hot.

Themrochromic pigments can be added to acrylic paints to make even more colour changes. If a blue thermochromic pigment which turns colourless when hot is added to yellow acrylic paint, the paint will appear green when cool and yellow when hot.

Phosphorescent pigments glow in the dark because:

-They absorb and store energy.

-They release the energy as light over a period of time.

Phosphorescent pigments are much safer than the older, altenative radioactive paints.