- When different elements combine, they form compounds.
- Metal + Non-Metal = ions formed.
- Metal atoms loose 1 or more electrons to form + charged ions.
- Non-Metal atoms gain electrons to form - charged ions.
- The oppositely charged ions attract strongly and the compond has ionic bonds.
- The chemical formula of ionic compound tells us the simplest ratio of ions in compound. For example, NaCl show that sodium chloride made from equal numbers of sodium and chloride ions.
- When non-metals combine, their atoms share electrons to form covalent bonds and molecules are formed.
- The chemical formula of a molecule tells us the no. of atoms that have bonded together in the molecule. For example, H20 shows that a water molecule contains 2 hydrogen and 1 oxygen atoms.
Limestone & its uses
- We quarry limestone because it has many uses.
- Blocks can be used for building.
- Limestone used to make calcium oxide and cement.
- Can make concrete by mixing cement with sand, aggregate & water.
- Limestone is mainly calcium carbonate CaCO3.
- When strongly heated, calcium carbonate decomposes to make calcium oxide and carbon dioxide.
- This is done on a large scale in lime kilns.
The equation is:
CaCO3 (Calcium Carbonate) -> Ca0 (Calcium Oxide) + CO2 (Carbon Dioxide)
- This type of reaction is thermal decomposition.
Reactions of carbonates
- All metal carbonates react in similar ways when heated or reacted with acids.
- They decompose to the metal oxide and carbon dioxide when heated strongly enough.
- Bunsen burner flame can't get hot enough to decompose sodium chloride or potassium carbonate.
- All carbonates react with acids to produce a salt, water and carbon dioxide gas.
- Limestone damaged by acid rain because calcium carbonate in the limestone reacts with acid in rain.
- Calcium hydroxide solution is called Limewater.
- Limewater is used to test for carbon dioxide.
- Limewater turns cloudy because reacts with carbon dioxide to produce insoluble calcium carbonate.
The limestone reaction cycle
- When heated strongly calcium carbonate in limestone decomposes to calcium oxide and carbon dioxide.
- When water added to calcium oxide they react to produce calcium hydroxide.
- Calcium hydroxide is alkali, can be used to neutralise acids.
- Calcium hydroxide is not very soluble in water but dissolves slighly to make limewater.
- Calcium hydroxide reacts with carbon dioxide to produce calcium carbonate, the main compound in limestone.
Cement and Concrete
- To make cement, limestone is mixed with clay and heated strongly in a kiln.The product is ground up to make a fine powder.
- Cement is mixed with sand and water to make mortar. Mortar is used to hold bricks and blocks together.
- Concrete is made by adding aggregate to cement, sand and water. Aggregate is small stones or crushed rocks.
- This mixture can be poured into moulds before it sets to form a hard solid.
- We depend on limestone to provide building materials. Cement and concrete are needed in most buildings.
- Quarrying limestone can have negtive impacts on the environment and on people living near the quarry.
- Cement works are often near limestone quarries.
- Making cement involves heating limestone with clay in large kilns. This uses a large area of land and a lot of energy.
- Rock that contains enough of a metal or metal compound to make it worth extracting is called an ore.
- Mining ores involves digging up large amounts of rock. The ore may need to be concentrated before the metal is extracted. These processes can produce large amounts of waste and may have major impacts on environment.
- A few unreactive metals, low in reactivity series, such as gold are found in the Earth as the metal. Gold is seperated from rocks by physical methods. However most metals are found as compounds, so the metals need to be extracted by chemical reactions.
- Metals are extracted from compounds by displacement using a more reactive element.
- Metals which are less reactive than carbon are extracted from the oxides using carbon reduction.
- Carbon reduction takes place when carbon removes the oxygen from the oxide to produce the metal.
Iron & Steels
- Many ores are used to produce iron contain iron (III) oxide. Iron (III) oxide is reduced at high temps in a blast furnace using carbon.
- The iron produces about 96% iron.
- The impurities make it hard and brittle & so it has only a few uses as cast iron.
- Removing all of the carbon & other impurities makes pure iron, but this is too soft for many uses.
- Most iron is used to make steels. Steels are alloys of iron because they are mixtures of iron with carbon and other elements.
- Alloys can be made so that they have properties for specific uses.
- The anounts of carbon & other elements are carefully adjusted when making steels. Low-carbon steels are easily shaped and high-carbon steels are hard.
- Some steels, such as stainless steels, contain larger quantities of other metals; they resist corrosion.
Aluminium and Titanium
- Aluminium has a low density, and although it is quite high in reactivity series, it is resistant to corrosion.
- Aluminium is more reactive than carbon and so its oxide can't be reduced using carbon.
- It has to be extracted by electrolysis by molten aluminium oxide.
- The process requires high temps. and a lot of electricity. This makes aluminium expensive to extract.
- Pure aluminium is not very strong, but aluminium alloys are stronger and harder. They have many uses.
- Titanium is resistant to corrosion and is very strong. It has a low density compared with other strong metals.
- Titanium oxide can be reduced using carbon, but the metal reacts with carbon making it brittle.
- Titanium is extracted from its ore by a process that has several stages and large amounts of energy. The high costs for the process makes titanium expensive.
- Copper can be extracted from copper-rich ores by smelting; this means heating ore strongly in a furnace.
- It produces impure copper, this can be purified by electrolysis.
- Smelting & purifying copper ore require huge amounts of heating and electricity.
- Copper-rich ores are a limited resource. Scientists are developing new ways of extracting copper from low-grade ores. These have less environmental impact than smelting.
- Phytomining uses plants to absorb copper compounds from the ground. The plants are burned & produce ash from which copper can be extracted.
- Bioleaching uses bacteria to produce solutions containing copper compounds.
- Solutions of copper compounds can be reacted with a metal that is more reactive to displacet the copper.
- Copper can be extracted from solutions of copper compounds by electrolysis.
- Elements from the centre block are known as transition metals.
- They are all metals & have similar properties.
- They are good conductors of heat & electricity.
- Many are strong, but can be bent or hammered into shape. This makes them useful as materials for buildings, vehicles, containers, pipes and wires.
- Copper is a good conductor of heat & doesn't react with water. It can be bent, but it hard enough to keep shape. This makes it useful for pipes and tanks in water & heating systems. It's a good conductor of electricity & is used for wiring.
- Most of the metals we use aren't pure elements.
- Pure iron, copper, gold and aluminium are soft & easily bent. They're often mixed with other elements to make alloys that are harder so that they keep shape.
- Iron is made into steels.
- Gold used for jewellery.
- Copper alloys include bronze and brass.
- Mining for ores involves digging and processing large amounts of rock. This can produce large amounts of waste & effect large areas of the environment.
- Recycling metals saves the energy needed to extract the metal. Recycling saves resources cause less ore needs to be mined. Less fossil fuel is needed to provide energy to extract metal from ore.
- Benefits of using metals in construction should be carefully considered against drawbacks.
Fuels from Crude Oil
- Crude oils contain many different compounds that boilat different temps. These burn under different conditions & so crude oil needs to be seperated to make useful fuels.
- We can seperate a mixture of liquids by distillation. Simple distillation of crude oil can produce liquids that boil within different temp. ranges. These liquids are called fractions.
- Most of the compounds in crude oil are hydrocarbons (molecules contain only hydrogen and carbon). Many of these are alkanes, with the general formula CnH2n+2. Alkanes contain as many hydrogen atoms as possible in each molecule and so we call them saturated hydrocarbons.
- We can represent molecules in different ways. A molecular formula shows the no. of each type of atom in each molecule, C2H6 represents a molecule of ethane. We can also represent molecules by a displayed formula that shows how the atoms are bonded.
- Crude oil is seperated into fractions at refineries using fractional distillation. This can be done because the boiling point of a hydrocarbon depends on the size of its molecule. The larger the molecule, the higher the boiling point of the hydrocarbon.
- The crude oil is vaporised and fed into a fractionating column, this is a tall tower that is hot at the bottom and gets cooler going up.
- Inside the column there are many trays with holes to allow gases through. The vapours move up the column getting cooler as go up. The hydrocarbons condense to liquids when reach the level that is their boiling point. Different liquids collect on trays at different levels & there are outlets to collect fractions.
- Hydrocarbons with smallest molecules have lowest boiling points & are collected at top. The fractions collected at bottom contain hydrocarbons with highest boiling points.
- Fractions with low boiling points have a low viscosity so they're runny liquids. They are very flammable. They also burn clean flames, producing little smoke. This makes them useful fuels.
- When pure hydrocarbons burn completely they are oxidised to carbon dioxide & water. But the fuels we use are not always burned completely, they may also contain other substances.
- In a limited supply of air incomplete combustion may produce carbon monoxide. Carbon may also be produced & some of the hydrocarbons may not burn. This produced solid particles that contain soot (carbon) & unburnt hydrocarbons called particulates.
- Most fossil fuels contain sulfur compounds. When it burns the sulfur compounds produce sulfur dioxide. This causes acid rain.
- At the high temperatures produced when fuels burn, oxygen and nitrogen in the air may combine to form nitrogen oxides. These also cause acid rain.
- We burn large amounts of fuels, this releases substances which spread through atmosphere and affect environment.
- Burning any fuel containing carbon produces carbon dioxide. This is a greenhouse gas, cause of global warming.
- Incomplete combustion of these fuels produces carbon monoxide (poisonous!). It also produces tiny solid particulates which reflect sunlight and cause global dimming.
- Burning fuels produces sulfur dioxide and nitorgen oxides. These gases dissolve in water droplets & react with oxygen in air, produces acid rain.
- Can remove harmful substances from waste gases before released into atmosphere. Sulfur dioxide removed from waste gases from stations. Exhaust systems fitted with catalytic convertors, removes carbon monoxide & nitrogen oxides. Filters remove particulates.
- Sulfur removed from fuels before supplied to users so less sulfur dioxide produced when fuel burnt.
- Biofuels made from plant or animal products. Are renewable.
- Biodiesel made from veg oil extracted from plants.
Advantages to biodiesel
- Makes little contribution to carbon dioxide levels, because the carbon dioxide given off when burns was taken from atmosphere by plants as grew.
Disadvantages to biodiesel
- Plants grown for biodiesel use large areas of farmland.
Ethanol made from sugar cane or sugar beet is biofuel. It's a liquid & can be stored & distributed like other fuels. Can be mixed with petrol.
Alternative Fuels (cont...)
HOW SCIENCE WORKS
- Using hydrogen as fuel produces only water when burned. But, it's gas so takes up large volume. Makes it hard to store in quantities needed for combustion in engines.
- Can be produced from water by electrolysis but requires large amounts of energy.
- Large hydrocarbon molecules can be broken down into smaller molecules by cracking.
Can be done in 2 ways:
- Heating a mixture of hydrocarbon vapours & steam to a v. high temp.
- Passing hyrdocarbon vapours over a hot catalyst.
- During cracking thermal decomp. reactions produce mixture of smaller molecules. Some smaller molecules are alkanes, which are saturated hydrocarbons. These alkanes with smaller molecules more useful as fuels.
- Some other smaller molecules formed are hyrdocarbons called alkenes, unsaturated hydrocarbons because they contain fewer hydrogen atoms than alkanes with same no. of carbon atoms.
- Alkenes have double bond between 2 carbon atoms & makes them more reactive than alkanes. Alkenes react with bromine water turning it orange -> colourless.
Making polymers from alkenes
- Plastics made from v. large molecules called polymers. These made from many small molecules joined together. Small molecules used to make polymers are monomers. The reaction to make a polymer is polymerisation.
- Lots of ethene molecules join together form poly(ethene), known as polythene. In polymerisation reaction double bond in each ethene becomes single bond and 1000s of ethene molecules join in long chains.
- Other alkenes can polymerise in similar way. e.g. propene forms poly(propene).
- Many plastics we use for bags, bottles, containers and toys made from alkenes.
New & Useful Polymers
- Scientists can design new polymers to make materials with special properties for specific uses. Many used for packaging, clothing and medical.
- New polymer materials for fillings been developed to replace mercury.
- Light senstive polymers used in sticking plasters.
- Hydrogels are polymers that trap water & used for dressing wounds.
- Shape memory polymers change back to their original shape when temp. or other conditions change. e.g. example of a smart polymer is stitches.
- The fibres used to make fabrics coated with polymers make breathable and waterproof.
- Plastic used in bottles, can be recycled to make polyester fibres for clothing.
- Many polymers not biodegradable. Means that plastic water not broken down when left. Unless disposed properly, plastic waste gets everywhere. Can harm wildlife. When put in landfill, takes up valuable space.
- We using more biodegradable plastics. Micro-organisms can break down these and they break down when contact with soil.
- Plastics made from non-biodegradable polymers have corn-starch mixed in, micro-organ can break this down and can be mixed with compost.
- Biodegradable plastics can be made from plant material. e.g. polymer made from cornstarch used as biodegradable food packaging.
- Some plastics recycled, but many ways of sorting and is difficult.
- Has formula C2H6O, often written as C2H5OH, shows the OH group in molecule, means an alcohol.
- Can be produced by fermentation of sugar from plant using yeast.
- Enzymes in yeast cause sugar to convert to ethanol & carbon dioxide. Made to make alcohol drinks.
- Can also be produced by the hydration of ethene.
- Ethene reacted with steam at high temp. in presence of a catalyst. Ethene obtained from crude oil via cracking.
- Ethanol produced by fermentation uses renewable resource (sugar from plants).
- Fermentation done at room temp. however can only produce dilute aqueous solution of ethanol. Ethanol must be seperated from solution by fractional distilltation, gives pure ethanol.
- Ethanol produced from ethene uses non-renew source (crude oil).
- Reaction run continuously & produces pure ethanol, requires high temp.
Extracting Veg Oil
- Some seeds, nuts & fruits rich in veg oils. Oil can be extracted by crushing & pressing plant material, then removing water and other impurities. Some oils extracted by distilling plant material mixed with water. Produces a mixture of oil and water, oil is seperated.
- When eaten, veg. oil provides lot of energy & important nutrients. Veg. oils release lot of energy when burnt in air, can be used as fuels. Used to make biofuels, e.g. biodiesel
- Molecules in veg oils have hyrdocarbon chains. Those with carbon-carbon double bonds (C=C) are unsaturated. If are several double bonds in each molecule, called polyunsaturated. Unsaturated oils react with bromine water, orange -> colourless.
Cooking with Veg Oils
- Boiling points of veg oils higher than water, food cooked at higher temps in oil. Cooks faster. Changes flavour, colour and texture. Some oil is absorbed and the energy content increases.
- Unsaturated oils can be reacted with hydrogen so some or all carbon=carbon bonds become carbon-carbon. Reaction called hydrogenation & done at 60*c using nickel catalyst. Hydrogenated oils have higher melting points, more saturated. Reaction also called hardening cause the hydrogenated oils are solid at room temp. Can be used as spreads, make pastries and cakes that require solid fats.
- Oil & Water don't mix & usually seperate, forming 2 layers. If shaken, tiny droplets form that are slow to seperate. This type of mixture is emulsion.
- Are opaque and thicker than oil and water made from. Improves texture, appearance & ability to coat and stick. Milk and cream are examples.
- Emulsifiers are substances that stop oil and water from seperating into layers. Most emulsions contain emulsifiers.
- Emulsifier molecules have a small hydrophilic part and long hydrophobic part. Hydrophilic attracted to water. Hydrophobic part attracted to oil. Hydrophobic parts of many emulsifier molecules go into each oil droplet & so droplets become surrounded by hydrophilic parts. Keeps droplets apart in water, preventing from joining and seperating.
Food Issues (HSW)
- Veg oils high in energy & important nutrients. Contain unsaturated fats, better for health than saturated.
- Animal fats and hyrdogenated veg oils contain saturated fats and are used in many foods. Linked to heart disease.
- Emulsifiers stop oil & water seperating. Makes food smoother & creamier. They taste better and less obvious that high in fat, may eat more.
Structure of Earth
- Earth is spherical, diameter about 12,800 km.
- Outer layer called crust. V thin, varies between 5km & 70km.
- Mantle under crust. About 3000km thick. Goes halfway to centre of Earth. Almost entirely solid but parts can flow v slowly.
- Core is half diameter of Earth. High proportion of magnetic metals iron and nickel. Liquid outer part, solid inner part.
- Atmosphere surrounds Earth. Most of the air within 10km of surface and most of atmosphere within 100km of surface.
- All raw materials and other resources that depend on come from crust, oceans and atmosphere. Resources limited.
- Crust and upper part of mantle cracked into tectonic plates. They move a few cm each year, due to convection currents in mantle. Convection currents caused by energy released by the decay of radioactive elements heating the mantle.
- Where plates meet, huge forces build up. Eventually, rocks give way, change shape or move suddenly causing earthquakes, volcanoes or mountains. Difficult to predict accurately when and where.
- Alfred Wegener created idea of continental drift in 1915. Other scientists didn't accept idea, he couldn't explain why. They believed Earth was shrinking as cooled. In 1960s new evidence found & theory of plate tectonics developed.
The Earth's atmosphere in the past
- Scientists think that Eath formed abt 4.5 billion years ago. In first billion years surface covered with volcanoes that released carbon dioxide, water vapour and nitrogen.
- As Earth cooled, most water vapour condensed forming oceans. Early atmosphere mainly carbon dioxide with some water vapour.
- Some scientists believe there was also nitrogen, possibly methane and ammonia.
- In the next 2 billion years, bacteria, algae & plants evolved. Algae & plants used carbon dioxide for photosynthesis and this released oxygen. As no. of plants increased the amount of carbon dioxide in atmosphere decreased & amount of oxygen increased.
Life on Earth
- Plants produced oxygen in atmosphere probably evolved from simple organisms like plankton and algae in ancient oceans.
- Don't know how molecules of simplest things were formed. Many scientists have theories but no evidence.
Miller - Urey Experiment
In 1952, 2 scientists did experiment based on what was thought to be early atmosphere. Used a mixture of water, ammonia, methane and hydrogen and a high voltage spark (simulate lightning). After 1 week, found that amino acids (the building blocks for proteins) had been produced.
Since 1950s theories about early atmosphere have changed, but scientists been able produce amino acids using other mixtures of gases. 1 theory suggests these organic molecules formed a 'primordial soup' & that amino acids in mixture combined to make proteins from which life began. Many other theories proposed, but no evidence.
Gases in Atmosphere
- Plants took up much of carbon dioxide in early atmosphere. Animals ate plants & much of carbon ended up in plant and animal remains as sedimentary rocks and fossils.
- Limestone was formed from the shells & skeletons of marine animals. Fossil fuels contain carbon and hydrogen from plants & animals.
- Carbon dioxide dissolves in oceans & probably formed insoluble carbonate compounds that were deposited on seabed & became sedimentary rocks.
- By 200 million years ago, proportions of gases in atmosphere stabilised. Atmosphere is almost 4/5 nitrogen and just over 1/5 oxygen. Other gases include carbon dioxide, water vapour and noble gases, make up about 1%.
Separating the gases in air
Gases in air have different boiling points & can be seperated from liquid air by fractional distilllation. It's done industrially to produce pure oxygen & liquid nitrogen, which have important uses. Air is cooled to below -200*c & fed into fractional distillation column. Nitrogen is seperated from oxygen & argon and further distillation used to produce pure oxygen and argon.