C1: The Revision Tackk...
C1a: Making Crude Oil Useful
Crude oil, coal, and natural gas are all fossil fuels. Fossil fuels are formed naturally over millions of years. They are finite and non-renewable, because they are used up much faster than new supplies can be formed, and will be all used up in the future. They are all easily extracted. Crude oil can be used as a source of fuel or chemicals. But it is finite, which means that it is being used up much faster than it is being replaced. Henceforth, scientists are now looking for alternatives to crude oil.
Crude oil is found in the Earth's crust. It can be pumped to the surface. Crude oil is transported to refineries through pipelines or in oil tankers. Accidents can cause oil spills from a tanker and the oil floats on the sea's surface as a slick. This can harm wildlife and damage beaches. This oil can affect lots of wildlife, including birds. The birds' feathers get stuck together and the birds may die. Detergents are used to break up the oil slick, but these chemicals are toxic and can harm or even kill wildlife.
Crude oil is a mixture of many hydrocarbons. A hydrocarbon is a molecule that contains only hydrogen and carbon atoms. Different hydrocarbons have different boiling points. This means that crude oil can be separated into useful fractions, (parts), that contain mixtures of hydrocarbons with similar boiling points. The process used is fractional distillation.
The crude oil is heated in a fractionating column. The column has a temperature gradient, which makes it hotter at the bottom of the column than at the top. Fractions with low boiling points leave at the top of the fractionating column, whereas fractions with high boiling points leave at the bottom of the fractionating column. One of the fractions is liquefied petroleum gas, (LPG). It contains propane and butane, which are gases at room temperature and are bottled. Below is a diagram of a fractionating column.
Hydrocarbon molecules can be described as alkanes or alkenes. Large alkane molecules can be broken down into smaller, more useful, alkane and alkene molecules. This industrial process is called cracking, and needs a catalyst, a high temperature and a high pressure. Cracking is used to make more petrol from naphtha. It can also be used to make alkene molecules that may be used to make polymers. There is, however, pressure on these limited resources.
There isn't enough petrol in crude oil to meet demand. So, cracking is used to change parts of crude oil that can't be used into additional petrol. Crude oil is found in many parts of the world, so oil companies have to work with many different countries to extract the oil. Oil is a very valuable resource and is more than often a source of conflict between countries.
In a hydrocarbon, there are strong covalent bonds between the atoms in the molecule. There are also weak intermolecular forces, (forces of attraction between molecules). The intermolecular forces between longer hydrocarbons are stronger than the forces between shorter hydrocarbons. When a liquid hydrocarbon is boiled, its molecules move faster and faster until all the intermolecular forces are broken and it becomes a gas. Small molecules have very weak forces of attraction between them and are easy to overcome by heating. It's the differences in their boiling points which allow us to separate a mixture of hydrocarbons, such as crude oil, by the process of fractional distillation.
C1b: Using Carbon Fuels
When fuels react with oxygen, (in the air), they burn, and release useful heat energy. This is called combustion, and it needs a plentiful supply of oxygen, (air). Many fuels are hydrocarbons. Complete combustion of a hydrocarbon, e.g. methane in air, produces carbon dioxide and water.
Methane + Oxygen -> Carbon Dioxide + Water; CH4(G) +2O2(G) -> CO2(G) +2H2O(L)
When fuels burn without enough oxygen, then incomplete combustion occurs. Some heat energy is released, but not as much as complete combustion. Incomplete combustion produces carbon monoxide, (a poisonous gas). This is why gas appliances should be serviced regularly.
Methane + Oxygen -> Carbon Monoxide + Water; 2CH4(G) + 3O2(G) -> 2CO(G) + 4H2O(L)
When very little oxygen is present, incomplete combustion of a hydrocarbon produces carbon, (in the form of soot), and water.
Methane + Oxygen -> Carbon + Water; CH4(G) + O2(G) -> C(S) + 2H2O(L)
Below is a diagram which compares both complete combustion and incomplete combustion, (and shows other potential by-products).
When choosing a fuel, you need to consider the energy value - how much energy is released from a gram of fuel; availability - how easy is it to access the fuel; ease of storage - how easy is it to store the fuel; cost - how much fuel do you get for your money; toxicity - is the fuel, (or its combustion products), poisonous; pollution - do the combustion products cause pollution; ease of use - is it easy to control, or is special equipment needed?
When using a fuel, you want complete combustion to happen because less soot is produced, more heat energy is released, and no carbon monoxide is made. As the world's population continues to grow, and more countries such as India and China become industrialised, the demand for fossil fuels continues to grow.
C1c: Clean Air
Today, clean air contains about 78% nitrogen, 21% oxygen, and 1% other gases, which includes 0.035% carbon dioxide. The levels of these gases stay about the same. Air also contains different amounts of water vapour. The levels of gas in the atmosphere are maintained by respiration; combustion, and photosynthesis.
All living things respire. They take in oxygen and give out carbon dioxide. Respiration and combustion decrease the oxygen levels and increase the carbon dioxide levels in the air. However, this is countered by plants. Plants photosynthesise; they take in carbon dioxide and release oxygen. Photosynthesis and respiration balance out, so the levels of carbon dioxide and oxygen in the air stay almost the same. Below is a bar chart depicting the approximate gaseous composition of the air.
The Earth's atmosphere hasn't always been the same as it is today. It has gradually changed over billions of years. The earliest atmosphere contained ammonia and carbon dioxide. These gases came from inside the Earth and were released through volcanoes. As plants developed, photosynthesis began and this reduced the amount of carbon dioxide and increased the amount of oxygen in the atmosphere.
The following is one theory used to explain how the Earth's atmosphere evolved...
A hot volcanic Earth released gases from the crust into the atmosphere. So, the initial atmosphere was made up of ammonia, carbon dioxide, and water vapour. As the Earth cooled, its surface temperature gradually fell below 100 degrees centigrade, and the water vapour condensed into liquid water. These newly formed oceans removed some carbon dioxide by dissolving the gas. The levels of nitrogen in the atmosphere increased as nitrifying bacteria released nitrogen. This gas is quite un-reactive. The level of oxygen in the atmosphere started to increase with the development of primitive plants that could photosynthesise. This removed carbon dioxide from the atmosphere, and added oxygen.
The air is becoming increasingly polluted with harmful gases due to human actions. Sulfur dioxide is made when fossil fuels that contain sulfur impurities are burned. It causes acid rain, which kills plants and aquatic life, and erodes stonework and corrodes ironwork. Carbon monoxide is a poisonous gas formed from incomplete combustion in a car engine. Oxides of nitrogen are formed in car engines. They cause photochemical smog and acid rain. Nitrogen and oxygen from the air react in the hot car engine to make nitrogen monoxide, (NO), and nitrogen dioxide, (NO2).
Three key factors have affected the balance of carbon dioxide that is removed from, and returned to, the atmosphere. The burning of fossil fuels is increasing the amount of carbon dioxide in the atmosphere; deforestation on large areas of the Earth's surface means that the amount of photosynthesis is reduced so less carbon dioxide is removed from the atmosphere, and an increase in world population had directly and indirectly contributed to the aforementioned factors.
It's important to reduce air pollution as much as possible, because it can damage our surroundings and can affect people's health. Carbon monoxide can be changed into carbon dioxide by a catalytic converter. Catalytic converters contain catalysts which help the polluting chemicals in exhaust gases to react with oxygen. Less harmful gases like carbon dioxide are produced instead. This helps to reduce the amounts of pollutants released into the atmosphere.
Carbon Monoxide + Nitrogen Oxide -> Nitrogen + Carbon Dioxide; 2CO + 2NO -> N2 + 2CO2
C1d: Making Polymers
Hydrocarbons are compounds that contain only carbon and hydrogen atoms. Carbon atoms can make four bonds each, whereas hydrogen atoms can make one bond each. To make a hydrocarbon, hydrogen atoms react with carbon atoms to form covalent bonds. When this happens, carbon atoms share a pair of electrons with hydrogen atoms to make a covalent bond.
When a hydrocarbon chain has only single covalent bonds, it is called an alkane. All of the carbon atoms make four single covalent bonds. The main chain will contain only single carbon-carbon, (C-C) bonds. The name of an alkane always ends in -ane. Alkanes contain only single covalent bonds - they are described as saturated hydrocarbons, (they have the maximum number of hydrogen atoms per carbon atom in the molecule). The following is a diagram, showing the names and molecular formulas of several alkanes.
When a hydrocarbon chain has one or more double carbon-carbon, (C=C) covalent bonds, it's called an alkene. Double bonds have two shaped pairs of electrons. The name of an alkene always ends in -ene. Alkenes have at least one double covalent bond, so the carbon atom isn't bonded to the maximum number of hydrogen atoms. Alkenes are described as being unsaturated. The following diagram shows the names and molecular formulas of several alkenes, (as well as their ball-and-stick model).
A simple test to distinguish between alkenes and alkanes is to add bromine water. Alkenes de-colourise bromine water, (the unsaturated alkene reacts with it), while alkanes have no effect on bromine water; the bromine water stays orange, (the saturated alkane can't react with it). This reaction is a test for un-saturation. It is an addition reaction between bromine water and the C=C to make a colourless dibromo compound.
The alkenes made by cracking are small molecules which can be used as monomers. The double bonds in alkenes are easily broken, so monomers can be joined together to make polymers, (large, long-chain molecules). Molecules in plastic are called polymers.
When the alkenes join together making a polymer, the reaction is called polymerisation. This process needs high pressure and a catalyst. You could use displayed formulae to show a polymerisation reaction. Below is a diagram showing the polymerisation formula of ethene monomers making poly(ethene).
Polymerisation involves the reaction of many unsaturated monomer molecules, such as alkenes, to form a saturated polymer. You should be able to construct the displayed formula of a polymer, if you're given the displayed formula of a monomer, and a monomer, if you're given the displayed formula of a polymer.
C1e: Designer Polymers
Different types of polymers, (plastics), have different properties. The uses of these polymers depend on their properties. For example, polythene, (or poly(ethene)), is light, flexible, is easily moulded, and can be printed on. Hence, it it used for plastic bags, as the plastic is flexible and light, and moulded containers, as the plastic is easily moulded. Polystyrene is light, and is a poor conductor of heat. Consequently, it is used as insulation, because it is a poor conductor of heat. Polyester is lightweight, waterproof, tough, and can be coloured, so it is used as clothing material, (the plastic can be made into fibres, is lightweight, tough, waterproof, and can be coloured), and in bottles, (the plastic is lightweight and waterproof).
Polymers like PVC are made of tangled, very long chain molecules. The atoms are held together by strong covalent bonds. Plastics that have weak forces between polymer molecules, (intermolecular forces) have low melting points and can be stretched easily, because 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, and are rigid, and henceforth, cannot be stretched.
Nylon has properties that make it ideal for outdoor clothing. These include the fact that it is lightweight, it is tough, it is waterproof, and it blocks UV light, (which is harmful sunlight). Although it is waterproof, (i.e. it keeps you dry), it doesn't let water vapour escape, so it can be uncomfortable if you become hot and start to sweat, (perspire).
Gore-Tex is a breathable material made from nylon. It has all of the advantages of nylon, but it's also treated with a material that allows sweat, (water vapour), to escape, while preventing rain from getting in. This is more comfortable than nylon, as it stops you from getting wet when you perspire.
In Gore-Tex, the nylon fibres are coated, (laminated), with a membrane of poly(tetrafluoroethene), (PTFE), or polyurethane. This makes the holes in the fabric much smaller. The coating is used with nylon because it is too weak to be used on its own. Below is a diagram of Gore-Tex, and how it prevents the entry of water droplets and allows the exit of water vapour.
We produce a lot of plastic waste, (polymers), which can be difficult to dispose of, and causes litter in the streets. There are three choices for the disposal of plastic waste, however, they all have disadvantages. Using landfill sites creates the problems of the wasting of valuable resources; landfill sites get filled up quickly and waste land, and most plastics are non-biodegradable, and will not be broken down by bacteria or decay. Burning polymers produces air pollution, and some plastics will produce toxic fumes when they are burned. Burning poly(chloroethene), (PVC), will produce hydrogen chloride gas. In addition, it wastes valuable resources. Recycling polymers also creates problems, as different types of plastic need to be recycled separately, and sorting plastics into groups can be both time-consuming and expensive.
Research is being undertaken on the development of biodegradable plastics. These plastics contain special parts which dissolve easily and break up the polymer chain. Biodegradable plastics are already being used in dishwasher detergent tablets.
CIf: Cooking and Food Additives
Cooking food causes a chemical change to take place. When a chemical change happens, new substances are formed, there is an energy change, and it can't be reversed easily. Eggs and meat contain lots of protein. When they are heated, the protein molecules change shape, (denature). This causes the texture and appearance of the food to change. For example, eggs change colour and solidify when heated. When potatoes are cooked, they soften and the flavour improves. Potatoes are a good source of carbohydrates.
Potatoes, and other vegetables, are plants, so their cells have a rigid cell wall. During cooking, the heat breaks down the cell wall, and the cells, as a result, become soft. Starch grains swell up and are released, so your body can easily digest them. Eggs and meat contain protein. Denaturing causes the protein molecules to change shape during cooking; it is an irreversible process.
Baking powder contains sodium hydrogen carbonate. When it is heated, it decomposes, (breaks down) to make sodium carbonate and water, and carbon dioxide gas is given off.
Sodium Hydrogen Carbonate -(Heat)-> Sodium Carbonate + Water + Carbon Dioxide
2NaHCO3 -(Heat)-> Na2CO3 + H2O + CO2
Baking powder is added to cake mixture because, as the mixture is heated, the carbon dioxide gas that is released causes the cake to rise. Limewater, (calcium hydroxide solution) can be used to test of carbon dioxide. If carbon dioxide is present, the limewater will change from colourless to milky. Below is a diagram showing how this is tested in the laboratory.
Food additives are substances that are put into food to improve it. A small number of people are allergic to certain food additives, i.e. they are harmed by them. There are different types of food additives. Antioxidants stop food reacting with oxygen in the air and increase the shelf life. Food colours improve the appearance of the food. Flavour enhancers bring out the flavour of a food without adding a taste of their own. Emulsifiers help mix oil and water, which would normally separate, for example, in mayonnaise.
Oil and water don't mix, so emulsifiers are used. The molecules in an emulsifier have two ends. One end likes to be in water, ( hydrophilic), and the other end likes to be in oil, (hydrophobic). The emulsifier joins the droplets together and keeps them mixed. The hydrophilic end of an emulsifier molecule attracts to the water molecules. The hydrophobic end of the emulsifier molecule attracts to the oil molecules. This attraction holds the water and oil molecules together, stopping them from separating. Below is a diagram of an emulsifier molecule.
Some cosmetics come from natural sources, such as plants and animals Examples of perfumes from natural sources include lavender, musk and rose. Cosmetics can also be manufactured. Manufactured perfumes are known as synthetic perfumes. Esters are a family of compounds, often used as perfumes. An ester is made by reacting an alcohol with an organic acid to produce an ester and water. Esters can be used as solvents. The following is a diagram of how esters can be made in the laboratory.
Smells are made of molecules which travel up your nose and stimulate sense cells. A perfume must smell nice, and must evaporate easily - so it can travel to your nose; not be toxic - so it doesn't poison you; not irritate - otherwise it would be uncomfortable on your skin; not dissolve in water - (i.e. it must be insoluble), otherwise it would wash off your skin easily, and it must not react with water - otherwise, it would react with your sweat. Perfumes are volatile, which means they evaporate easily. The molecules of perfume are held together by weak forces of attraction. The molecules that have lots of energy can easily overcome the weak forces of attraction and escape.
Perfumes and cosmetics need to be tested to make sure they are safe to use. This testing is sometimes done on animals, although testing on animals has been banned in the EU. An advantage of animal testing is that it prevents humans from being harmed, while disadvantages of animal testing include that it's cruel to animals, and animals don't have the same body chemistry as humans, so the results may not be useful.
Here are some words used to describe substances: soluble substances are substances that dissolve in a liquid. For example, nail varnish is soluble in ethyl ethanoate, (nail varnish remover). Insoluble substances are substances that don't dissolve in a liquid. Nail varnish is insoluble in water. A solvent is the liquid into which a substance is dissolved. Ethyl ethanoate is a solvent, (an ester can be used as a solvent). The solute is the substance that gets dissolved. The nail varnish is the solute. A solution is what you get when you mix a solvent and a solute; it will not separate out.
Nail varnish dissolves in nail varnish remover, (ethyl ethanoate) but not in water. Nail varnish will not dissolve in water because the attraction between water molecules is stronger than the attraction between water molecules and nail varnish molecules. In addition, the attraction between the molecules in nail varnish is stronger than the attraction between water molecules and nail varnish molecules.
C1h: Paints and Pigments
Paint is a colloid. Colloids are made of small, solid particles that are mixed well, (dispersed, but not dissolved), with liquid particles. Paint is a mixture of pigment, which is a substance that gives paint its colour; binding medium, which is an oil that sticks the pigment to the surface that it's being painted on to, and a solvent, which thins the thick binding medium and makes it easier to coat the surface. The following is a very basic representation of a colloid in liquid.
Paint can be used to protect and to decorate a surface. It coats the surface with a thin layer and dries when the solvent evaporates. The solvent in emulsion paint is water. In oil-based paints, the pigment is dispersed in an oil, (the binding medium). Often, there is a solvent present that dissolves the oil.
The particle size of the solids in a colloid must be very small so they stay scattered throughout the mixture. If the particles are too big, they settle down to the bottom of the mixture. An oil-based paint, such as a gloss paint, dries in two stages. The solvent evaporates away, and the oil-binding medium reacts with oxygen in the air, (an oxidation reaction), as it dries to form a hard layer.
Thermochromic pigments change colour when they are heated or cooled. These pigments can be used to coat kettles and cups to indicate the temperature, in mood rings, and in toys and cutlery for babies to warn if food or bath water is too hot.
Phosphorescent pigments glow in the dark. They absorb and store energy and then release it as light when it's dark.
A thermochromic pigment can be added to acrylic paints, which makes the paint change through more colours. The first "glow-in-the-dark" paints were made using radioactive material as pigments and were used for things like watches. But, they were too dangerous, as they exposed people to too much radiation. Phosphorescent pigments aren't radioactive, so they are much safer to use.
End of C1...
This Has Been a GrumblingGrenade Tackk, (@HarbingerOfNonsense), Thank You Very Much For Your Time.
All content on this Tackk is from the OCR Gateway GCSE Chemistry B Revision Guide.