Chemistry C3

Organic Chemistry

Formula for alkanes : CnH2n+2       Formula for alkenes: CnH2n      Formula for alcohols: CnH2n+1OH

Alkanes: Methane, Ethane, Propane, Butane, Pentane etc.     Alkenes: Ethene, Propene, Butene etc.

Alcohols: Methanol, Ethanol, Propanol, Butanol etc.

Isomers are molecules with the same molceular formula but different structural formula.

Enzymes are biological catalysts. Enzymes work best at their optimum temperature. Low temperature slow down the reactions and high temperatures denature the enzymes.

Fire triangle - fuel, heat and oxygen.

Removing heat - water e.g on bonfires, housefires

Removing fuel - fire breaks e.g forest fires, turning gas supply off e.g natural gas fire

Removing oxygen - CO2 e.g electrical fires, foam e.g aeroplane fires.

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Ethanol

Fermentation is the process used to brew alcohol. It is anaerobic respiration in yeast. Glucose --> carbon dioxide + ethanol. C6H12O6 --> 2CO2 + 2C2H5OH. If the alcohol concentration gets too high, the yeast is killed. Distillation is used to make higher concentrations. Distillation works because ethanol has a lower boiling point than water so it is boiled off first when heated. It passes through a condensor and is collected as pure ethanol. 

Ethanol can also be made by hydration of ethene with steam. Ethene + steam --> ethanol. C2H4 + H2O --> C2H5OH. Ethanol is found in alcoholic drinks. This has social and health problems - depression, liver damage, violence. It can also be used a as a fuel and a solvent.  

Ethanol as a fuel - can be made from ethene or fermentation. Advantages of ethene - one-stage process, 95% conversion. Disadvantages - ethene comes from crude oil, high energy cost - high temperature and pressure. Advantages of fermentation - cheap raw material, renewable plant material, conserve fossil fuels, low cost process, because of low temperature. Disadvantages - 15% mixture must be concentrated and purified by distillation - two stages - extra cost.

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Carboxylic acids and esters

If ethanol is mixed with air ethanoic acid is formed.- vinegar. Ethanoic acid is weak because it doesn't disociate completely so there are less H+ ions. Sulphuric acid is stronger as it has more H+ ions.  Carboxylic acids have the COOH functional group. (methanoic, ethanoic and propanoic acids etc.) They are weak because they don't ionise completely when dissolved in water. Reactions with carbonates are slow.

Ethanoic acid + potassium carbonate --> potassium ethanoate + carbon dioxide + water

Reactions with alcohols produce esters. Presence of acid catalyst is needed. Usually sulfuric acid.

Ethanoic acid + propanol --> propyl ethanoate + water.

Esters are sweet-smelling organic compounds, many of which are found in fruits. Used as flavourings and perfumes.

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Haber process and Contact process

In the haber process nitrogen reacts with hydrogen to from ammonia. The reaction is reversible. N2 + 3H2 <--> 2NH3. For ammonia to form the reaction is exothermic, from left to right. A temperature of 450 and pressure of 200 atmospheres is used. Also an iron catalyst.  Any unreacted hydrogen and nitrogen is recycled. on cooling, ammonia liquifies and is removed.  Lower temperature is favoured to produce a higher yield because as temperature increases the reaction wants to go from right to left to reduce the temperature and maintain equilibrium. The temperature is compromised because if it was too low the rate of reaction would be too slow. Higher pressures are favoured to produce a high yield however it is expensive and potentially dangerous so a compromise of 200 atmospheres is used. The catalyst speeds up the reaction.

Sulphur is burned in air. S + O2 --> SO2. (reacts with oxygen to form sulphur dioxide). Sulpur dioxide is reacted with more oxygen to form sulphur trioxide. This is a reversible reaction. 2SO2 + O2 <--> 2SO3. Passed over vanadium pentoxide catalyst. The sulphur trioxide is dissolved in concentrated sulphuric acid before adding water because it is too exothermic. This makes Oleum which is carefully mixed with water to form Sulphuric acid. H2O + SO3 --> H2SO4

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Sulphuric acid/ Fertilisers

Sulphuric acid is a dehydrating agent. It removes water from sugar, paper and wood. The oxygen and hydrogen is removed leaving carbon. It also removes water from hydrated copper sulphate which changes colour from blue to white and loses its crystalline apperance.

Used to make fertilisers such as ammonium sulphate.

Fertilisers increase crop yield. However if too much is used, eutrophication can happen. This is when the fertiliser gets into water and causes algae to grow. The algae blocks sunlight and plants can't do photosynthesis so no oxygen is made. Bacteria uses up the oxygen so fish can't do respiration and die.

Acid + base --> salt + water

Sulphuric acid + ammonium hydroxide --> ammonium sulphate + water.

A titration is done to find out how much acid is needed to neutralise the alkali so there isn't indicator in the fertiliser. When made, the fertiliser is dissolved in water so needs to evaporate and then the solution crystallises and the crystals are filtered off.

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Titration and mole calculations

Mr      CaCO3  ( Ca -40, C-12, O-16)    40 + 12 + (16x3) = 100

moles = mass / formula mass

concentration = moles / volume (in litres)

Example - In a titration 25.0 cm3 of sodium carbonate solution required 24.2 cm3 of 0.200 mol dm-3 hydrochloric acid to be exactly neutralised. ( a burette and pipette is used in a titration)

Na2CO3 + 2HCl --> 2NaCl + CO2 + H2O

what was the concentration of the sodium carbonate solution in both mol dm-3 and g dm-3?

hydrochloric acid - moles = concentration x volume 0.0242 x 0.200 = 0.00484 moles

0.00484 / 2 = 0.00242

0.00242 / 0.025 = 0.0968 mol dm-3  Na2CO3 = 106  x 0.0968 = 10.26 g dm-3

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Limestone

Thermal decompostion is breaking down with heat. Calcium carbonate is thermally decomposed into calcium oxide and carbon dioxide. CaCO3 --> CaO + CO2

Sodium carbonate NaCO3 --> NaO + CO2     Copper carbonate CuCO3 --> CuO + CO2

Calcium oxide A.K.A quicklime.This reacts with water to form calcium hydroxide A.K.A slaked lime.

CaO + H2O --> Ca(OH)2

Limewater reacts with carbon dioxide to form limestone again.

Ca(OH)2 + CO2 --> CaCO3 + H2O. The carbon dioxide turns limewater cloudy.

Limestone is used to neutralise acidic soils, in construction to make cement, bricks etc., in toothpaste, in production of iron and steel and to build roads. However quarrying creates noise pollution, it is visually intrusive (spoils the view) and explosions can shake nearby houses. Also there is a lot of pollution (smog) and congestion from lorries. Loss of wildlife habitats.

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Chemical analysis

Test for hydrogen - squeaky pop when lit splint put in.   Test for oxygen - relights glowing splint.   Test for carbon dioxide - turns limewater milky. Test for ammonia - when heated with sodium hydroxide, turns damp red litmus paper blue, pungent smell. Flame tests - sodium - orange/yellow, potassium - lilac, calcium - red, copper - green/blue, barium - green, lithium - crimson.Testing with sodium hydroxide. -

Cu+ ions. Blue precipitate - copper(ii) hydroxide. Cu2+ + 2OH-  --> Cu(OH)2  

Fe2+ ions. green gelatinous precipitate - iron(ii) hydroxide. Fe2+ + 2OH- --> Fe(OH)2

FE3+ ions. Brown gelatinous precipiate - iron(iii) hydroxide. Fe3+ + 3OH- --> Fe(OH)3  Testing for carbonates - produce carbon dioxide. Testing for halides - Silver nitrate solution - chloride - white precipitate, Bromide - cream precipitate, iodide- yellow precipitate. AgNO3 + XY (x is metal, Y is halide)  --> AgY + YNO3. Ag+ + X- --> AGX.

Testing for sulphates. barium chloride solution. White precipitate. Barium chloride + sulfate ion --> barium sulfate. Atomic spectroscopy is used to identify and find concentrations of atoms or ions.

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