- Limestone consists of mainly calcium carbonate- CaCO
- Used to create glass, cement and concrete
- When we heat limestone strongly, it breaks down to form quicklime or calcium oxide- CaO. This is called thermal decomposition, also producing carbon dioxide:
Calcium carbonate - calcium oxide + carbon dioxide
CaCO3 - CaO + CO2
Quicklime and Slaked Lime
- When we add water to quicklime we get slaked lime or calcium hydroxide- Ca(OH)2
Calcium oxide + Water - Calcium hydroxide
CaO + H2O - Ca(OH)2
- This reaction (above) is exothermic, as it emits heat
- We dissolve calcium hydroxide in water in small amounts, after filtering, producing lime water. When carbon dioxide is bubbled through clear lime water, turn cloudy, as calcium carbonate is formed.
Cement, Concrete and Glass
- Heating limestone with clay in kiln produces cement
- Limestone... heated with clay + other minerals = Portland cement. This is ground into fine powder. Solution is mixed with sand and water, so used for building materials.
- Adding crushed rocks to mixture of cement, sand and water makes concrete.
- When powdered limestone heated with sand and soda (sodium carbonate) forms glass.
- Metals found in Earth's crust, most combined with other elements (oxygen)= being chemically seperated from compounds.
- Rock containing metal = metal ore
- Some metals are unreactive, they don't combine with other elements (e.g. gold, silver, platinum) found in native state
- extract metals depending on place in reactivity series- more reactive metal, displace less reactive metal from compound. Or carbon (non-metal) also displace less reactive metal from oxide. Or use carbon to extract metals from ores commerically.
- metals found in metal oxide form like copper, lead and zinc. as carbon is more reactive than these metals, use it to extract from their ores.
- When heat metal oxide with carbon, carbon removes oxygen, forming carbon dioxide leaving pure elements behind:
metal oxide + carbon - metal + carbon dioxide
Extracting Irons- The Blast Furnace
- Iron second most common ore in crust and iron ore contain oxygen. Iron less reactive than carbon, remove oxyygen from ore using carbon.
- We extract iron using blast furnace.
- Blast furnace, enter 3 substances:.... haematite- most commone iron ore, containing iron (III) oxide and some sand- Fe2O3.... substance made from coal, almost pure carbon called coke...... and limestone.
- hot air blown into furnace, making it heat, forming carbon dioxide as coke reacts with oxygen.
C + O2 - CO2
- CO2 reacts with coke second time, forming carbon monoxide
CO2 + C - 2CO
- Carbon monoxide reacts with iron oxide, removing oxygen and reducing molten iroon, flowing out of the bottom of the furnace
Iron and Steels
- Iron produced by blast furnace- about 96% iron, called pig iron.
- Pig iron contains carbon,treat it to remove this carbon.
- Removing carbon + impurities makes pure iron. Is soft and bendy, meaning NOT useful. To make useful, ensure it has tiny amount of other elements, including carbon.
- Call metal containing other elements alloy.
- Call iron which has had other elements alloyed to steel.
- Low- alloy steel contains 1%-5% of other elements, more expensive than carbon steel.
- High- alloy steels contains 12%-15% other elements, even more expensive to make. Example- chromium- nickel steel/ stainless steel. often used cooking utensils and cutlery.
- Copper useful metal
- Bronze, first alloy made, formed by alloying copper with tin- also adding range of other elements giving bronze different properties.
- Brass made from alloying copper with zinc.
- aluminium is metal with over 300 alloys. Can be alloyed with many elements.
- we bend (or deform) alloys and heat, some will return to original shape. THese shape memory alloys (SMas) are examples of smart alloys.
Definition: A smart alloy is a smart material that can remember its original shape.
Aluminium and Titanium
- Aluminium metal has many uses. Useful properties is that is is a reactive metal but it doesn't corrode easily.
- Most common aluminium ore is bauxite, mined using open-cast mining
- Carbon less reactive than aluminium, carbon won't reduce aluminium oxide to aluminium, instead we use electrolysis
- Electrolysis requires a lot of electricity. Aluminium oxide must be liquid form, so high temperatures are needed. during process, aluminium forms at negative electrode and oxygen forms at positive electrode. Oxygen reacts with carbon electrode and lost of carbon dioxide + carbon monoxide formed. Aluminium released from electrolysis cell as a liquid.
- Crude oil made of many different chemical compounds
- Crude oil contain hydrocarbons, compounds of carbon and hydrogen atoms only.
- Hydrocarbons are saturated called alkanes. Being saturated means they have as much hydrogen in molecules as possible.
- Separate crude oil using fractional distillation
- Chains of hydrocarbons vary in size and differently sized hydrocarbon chains have different properties.
- Separate crude oil into fractions, which are groups of hydrocarbons with similar amounts of carbon atoms.
- Each of these fractions boil at different temperatures because number of atoms per molecule.
- Crude oil is fed into bottom of fractioning column as hot vapour. Tower is kept at high temperatures at bottom and cooler at top. Column decreases in temperature as you go up column.
- Different gases condense when they reach boiling points and different fractions are collected at different levels.
- Hydrocarbons with smallest molecules have lowest boiling points, cool to form thick liquids or solid room temperature.
- Burning hydrocarbons releases substances such as carbon dioxide into the atmosphere.
- Some substances dissolve into droplets of water and fall as acid rain.
- Carbon dioxide released by burning fuels is a greenhouse gas, reduces the rate at which energy is lost from surface of the Earth by radiation.
- Use cleaner fuels which don't release any or as much greenhouse gases e.g. gasohol.
- Break down hydrocarbons in process called cracking
- Cracking normally carried out at high temperatures using catalyst. Known as catalytic cracking.
- Catalytic cracking happens in cat crackers:
Fraction produced from crude oil is heated to form a gas
Hydrocarbon gas is passed over a hot catalyst where thermal decomposition takes place.
Larger molecules split apart form smaller molecules. More useful.
- Some hydrocarbons are unsaturated because they have carbon=carbon double bonds. Called alkenes.
- Make chemicals from crude oil, which we use to make plastics.
- Plastics are made from huge molecules which consist of many smaller molecules joined together. Smaller molecules are monomers and larger molecules are called polymers.
- Able to make different plastics which have different properties.
- Ethene (C2H4) is smallest unsaturated hydrocarbon molecule. Turn into a polymer, known as ply(ethene).
- Monomers join together when double bonds in alkenes 'open up', replaced by single bonds of thousands of other molecules joining together.
- This reaction is an additional reaction, since a polymer is made, we call it addition polymerisation.
- Atoms in polymer chains are very strong, size of forces between the molecules differ for different plastics. Call these forces between molecules intermolecular forces and size of them depend on: *monomers used and conditions we choose to carry out polymerisation.
- Some plastics, intermolecular forces waken when heated and bonds become strong again when cooled. Plastics that behave in this way are thermosoftening plastics. Examples of this.... poly(ethene) etc.
- some bonds made to be so strong when formed that they cannot be softened. plastics like this, useful for things such as kettles, called thermosetting plastics.
Extraction of Plant Oils
- Use distillation or pressing to extract vegetable oils.
- Distillation involves boiling the plant and condensing the evaporated oils released and removing water and other impurities.
- Vegetable oils have chains of carbon atoms with hydrogen atoms attached.
- Some vegetable oils have carbon=carbon double bonds. These are unsaturated oils.
- Test for unsaturated oils using either bromine water or iodine solution: * originally, bromine water is orange/yellow, turn colourless if it meets unsaturated vegetable oil. * iodine solution is red/violet, turning colourless if it meets an unsaturated vegetable oil.
Cooking with vegetable oils
- vegetable oils are useful in cooking because: they have a high boiling point and so foods can be cooked in them at very high temperature. They allow food to absorb the oils, increasing their energy content.
- vegetable oils can be hardened where they are reacted with hydrogen to increase their melting and boiling points.
- To make oils harden, you must use a nickel catalyst and carry it out at around 60C
- Oils that have been treated this way are called hydrogenated oils, as they are solid at room temperature. Meaning they can be made into spreads- butter, margarine etc.
- Oils DON'T naturally dissolve or mix with water
- Oils used produce emulsions, having special properties.
- Emulsifiers DON'T dissolve oils in water, simply mix smaller droplets of oil in water.
- Emulsions made from vegetable oils used in foods such as salad dressings and ice creams.
What substances are added to our food?
E2 preserves help keep food lives last longer
E1 Colours- Improves appearance of food
E3 Antioxidants- Stop food from reacting with oxygen
E4 Emulsifiers- Help improve texture of food
E5 Acidity regulators- Help control foods pH
E6 Flavouring- improve taste of food
- Detect unknown food additives using chromatography by comparing their chromatographs against those substances we already know.
- Also use mass spectrometer.
Structure of the Earth
- Earth made up of layers formed millions of years ago, when heavy materials sank to centre of planet and lighter materials floated up top.
- Crust and uppermost part of mantle make up Earth's lithosphere
- Crust is outermost layer, ranging from 6km under oceans to 35km under continents.
- Mantle found under crust behaves like solid, able flow very slowly
- Core made up of two parts- outer core and inner core. Both made of nickel and iron and outer core liquid whilst inner core is solid.
Earth's atmosphere in the past
- Early atmoshpere compressed, large amounts of carbon dioxide, water vapour, methane and ammonia.
- Earth's surface cooled below 100C, steam condensed form oceans
- Oceans absorbed carbon dioxide, carbon dioxide concentration in atmosphere fell dramatically.
- 3000 million years ago, simple life developed and by photosynthesis happening, carbon dioxide concentrarion further dropped. Oxygen produced.
- Absence of air, temperatures combined with pressure formed fossil fuels, reducing carbon dioxide concentration.
- Shell formations in ocean reduced carbon dioxide levels
- Ammonia removed via nitrification of bacteria (as they evolved) turning ammonia into nitrates
- Denitrifying of bacteria turned the nitrated into nitrogen
- Oxygen and ammonia reacted to form water vapour and nitrogen
Earth's atmosphere today
- The atmosphere on planet roughly same as it was 200 million years ago:
0.04% carbon dioxide
trace amounts of other gases.
- Carbon cycle shows carbon rotates between rocks, oceans and atmosphere
- Oceans absorb excess carbon dioxide and produce it when it is needed- making them useful carbon dioxide reserviors.
- Plants take in carbon dioxide during process of photosynthesis
- Therefore, plants and oceans play good carbon dioxide sinks
- Carbon dioxide released back into atmosphere when animals and plants respire, as well as when dead animals bodies decompose.