Chemistry Topic 5

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Where are most metals found?
In ores. If the metal reacts with other elements to form compounds, and the compound contains enough of the metal it is worthwhile to dig them up from the Earth's crust.
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What is a reduction reaction?
A reaction that separates a metal from the oxygen in its oxide.
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What is a reducing agent in a reduction reaction?
The substance that reduces the metal and is oxidised. The most common type of reduction reaction uses carbon as a reducing agent, but only if the metal is less reactive than carbon. This is done by heating the ore with carbon monoxide.
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What is extracted using electrolysis?
Potassium, Sodium, Calcium, Magnesium, Aluminium.
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What is extracted by heating with carbon monoxide?
Zinc, Iron, Tin.
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What is the basics of electrolysis of aluminium?
Removes Al from its ore. Main ore is bauxite, after mining and purifying a white powder is left (Al2O3- pure aluminium oxide).
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What are the conditions for electrolysis of aluminium?
Al2O3 has a very high melting point (over 2000degrees)- very expensive.Al2O3 dissolved in molten cryolite to bring the temperature down to about 900degrees. Electrodes are made of graphite- good conductor of electricity.
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How does the electrolysis of aluminium work?
Molten aluminium oxide conducts electricity, free ions. Positive Al^3+ ions attracted to cathode, pick up electrons and turn into aluminium atoms. -ve O^2- ions attracted to anode&lose electrons, react together and form O2 and some form CO2.
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Why does the positive carbon electrode need replacing often in the electrolysis of aluminium?
Always being worn down in this redox reaction.
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Negative electrode- cathode- equation for electrolysis of aluminium.
Al^3+ + 3e^- -> Al . REDUCTION- a gain of electrons.
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Positive electrode- anode- equation for electrolysis of aluminium.
2O^2- -> O2 + 4e^- . OXIDATION - a loss of electrons.
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Why is electrolysis expensive?
Uses a lot of electricity, energy is needed to heat the electrolyte mix. Disappearing positive electrodes need frequent replacement.
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What is the process of extraction iron?
Extracted from haematite by reduction in a blast furnace. Iron ore-iron, coke-pure carbon,limestone-takes away impurities in form of ****.
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How do you reduce the iron ore to iron in a blast furnace?
Hot air->furnace. Coke burns faster than usual, [email protected] C + O2 -> CO2. CO2 + C (unburnt coke) -> 2CO (carbon monoxide). 3CO + Fe2O3 -> 3CO2 + 2Fe. Iron molten is dense so runs straight to bottom and is tapped off.
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How do you remove the impurities in a blast furnace?
Main impurity is sand- silicon dioxide. Sold at 1500, limestone removes it. Limestone decomposed by heat- CaCO3 -> CaO + CO2. CaO + SiO2 (sand) -> CaSiO3 (molten ****). Cooled ****-solid- road building, fertiliser.
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What properties do iron and aluminium share?
Dense and lustrous (eg shiny), high melting points, high tensile strength, malleable, good conductors of heat and electricity.
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What are the uses of iron?
Wrought iron nearly 100% pure- malleable, used to make ornamental gates and railings. Mix iron with other elements-> alloys; cast iron-Iron,C,Si- brittle+hard, cooking pans; steel-car bodies,girders. Stainless steel-allow of iron+chromium,forks.
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What are the uses of aluminium?
Doesn't corrode easily, reacts quickly with O2 in air to form aluminium oxide which acts as a protective layer to prevent . Drinks cans, bicycle frames and aeroplanes.
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What are the uses of aluminium?
Doesn't corrode easily, reacts quickly with O2 in air to form aluminium oxide which acts as a protective layer to prevent further reactions. Drinks cans, bicycle frames and aeroplanes.
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Fractional distillation of crude oil.
Oil is heated-most turns into gas. Gases enter fractionating column and liquid bitumen drained off at bottom.Temperature gradient,substance reaches part of column where temp is lower than their boiling point-condenses back into a liquid.
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What stops the liquids from running back down the column in fractional distillation?
Bubble caps. Longer hydrocarbons have high boiling points, condense and drain out of column early on. Shorter hydrocarbons have lower boiling points, drain out later.
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Describe the order of the fractions (shortest hydrocarbon chain *TOP* -> longest hydrocarbon chain *BOTTOM*)
Refinery gases, gasoline, naphtha, kerosene, diesel, fuel oil, bitumen.
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What can refinery gases be used for?
Heating, pottery and glass manufacture- where a clean-burning fuel is needed.
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What can gasoline be used for?
Fuel for cars.
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What can naphtha be used for?
Starting material to make plastics, dyes, drugs, explosives etc
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What can kerosene be used for?
Jet engines, domestic heating, paint solvent.
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What can diesel be used for?
Fuel for diesel engines in cars, trucks etc.
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What can fuel oil be used for?
Domestic central heating.
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What can bitumen be used for?
Road surfacing and asphalt for roofs.
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Give some examples of pollutants burning fuels can produce.
Carbon monoxide, nitrogen oxides, and sulfur dioxide.
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How is carbon monoxide produced?
Incomplete combustion. It is poisonous, can stop body carrying oxygen- combines with haemoglobin in blood cells - can lead to fainting, a coma, or death.
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How are sulfur dioxide and nitrogen oxides produced?
From burning fuel. Sulfur dioxide comes from sulfur impurities in fossil fuels. Nitrogen oxides are created when the temp is high enough for N and O in air to react.
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What is acid rain caused by?
Sulfur dioxide and nitrogen oxides. CO2(g) + H2O(l)->H2CO3(aq)(carbonic acid)---- rain is acidic because of this. 2SO2(g)+O2(g)+2H2O(l)->2H2SO4(aq)---mixes with clouds forming dilute sulfuric acid.
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What is cracking?
A form of thermal decomposition. Breaking molecules down into simpler molecules by heating them. It produces alkenes, which are used to make polymers.
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What are the conditions for cracking?
Heat, and a catalyst.
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What are the conditions for cracking in industry?
Vaporised hydrocarbons passed over powdered catalyst (silica or alumina) at about 600-700degreesC.
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Experiment to show cracking paraffin in the lab.
Heat paraffin->few seconds-move bunsen burner-heat catalyst. Alternate between both until paraffin vaporises&catalyst glows red. Heated paraffin vapour cracks- passes over heated catalyst. Small alkanes collect end tube.Alkene gases travel down tube.
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Addition polymers.
Momomers that make these up have a C=C double bond (ALKENES). Under high pressure&w/ catalyst, small molecules open up. Double bonds polymerise to form long saturated chains (polymers).
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How do you show polymers using repeating units?
.
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Condensation polymerisation.
Usually involves two different types of monomer. Monomers react together, bonds form between them making polymer chains. Each new bond formed-small molecule lost. Nylon is an example.
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What are the uses of polymers?
Poly(ethene) - light & stretchable -packaging, eg plastic bags ,bottles. Poly(propene) -tough & flexible & heat resistant ,eg kettles ,food containers. Poly(chloroethene) -clothes ,pipes ,insulating electrical cables.
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Why are most polymers hard to get rid of?
Mdst addition polymers are inert, C=C double bonds are strong and not easily broken. Takes a long time for them to biodegrade, bury them and the'll be there years later. Burning plastics can release toxic gases-avoid doing this.
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The making of ammonia.
N2(g)+3H2(g)2NH3(g)+(Heat). Nitrogen obtained from air, H2 from natural gas/cracking hydrocarbons. Reaches a dynamic equilibrium. 200atm, 450degreesC, iron catalyst.
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How does the Haber Process reach the dynamic equilibrium?
High pressure favour forward reaction, pressure is set as high as possible-200atm is high but not too expensive. Forward reaction=exothermic. Inc. temp will favour other side, so lower temp needed-450 is a compromise, yield and speed of reaction.
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How does the Haber Process reach the dynamic equilibrium? (2)
Ammonia formed=gas, cools in condenser and liquefies, removed. Used H2 and N2 are recycled, no waste. Iron catalyst makes reaction faster but doesn't affect the yield.
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What is ammonia used to make?
Nitric acid - in Ostwald process. Ammonium nitrate fertiliser- plants need nitrogen to make proteins- more effective, two sources of nitrate.
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What is the contact process used to do?
To make sulfuric acid.
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What are the stages in the contact process?
S+O2->SO2, burning S in air or roasting sulfide ores. 2SO2+O22SO3,oxidised. SO3+H2SO4->H2S2O7,dissolved,form liquid oleum. H2S2O7+H2O->2H2SO4, diluted to form concentrated sulfuric acid.
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What are the conditions for the contact process?
450degreesC, 2atm, Vanadium(V) oxide cataylst (V2O5).
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What are the modern industry uses of sulfuric acid?
Fertilisers-phosphate fertilisers. Detergents-cleaning. Paints-titanium dioxide, white pigment in paint.
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The electrolysis of brine (sodium chloride solution).
Concentrated brine is electrolysed industrially using a diaphragm cell. H2 gas given off at cathode,become 1 H molecule. Cl(g) given off at anode, 1 Cl molecule. Sodium ions stay in solution w/ hydroxide ions. Sodium hydroxide left in solution.
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What are the half equations for the electrolysis of brine?
Cathode: 2H_ _ 2E- -> H2. Anode: 2Cl- -> Cl2 + 2e-
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What useful products are made by the electrolysis of brine?
Chlorine-sterilise water supplies, make bleach and HCl. Hydrogen-used in Haber process, change oils into fats for margarine. Sodium hydroxide:chemical industry, soap, bleach, paper pulp.
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Card 2

Front

What is a reduction reaction?

Back

A reaction that separates a metal from the oxygen in its oxide.

Card 3

Front

What is a reducing agent in a reduction reaction?

Back

Preview of the front of card 3

Card 4

Front

What is extracted using electrolysis?

Back

Preview of the front of card 4

Card 5

Front

What is extracted by heating with carbon monoxide?

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Preview of the front of card 5
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