Section 4: Organic Chemistry
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What is the general formula of an alkane and alkene
Alkane = CnH2n+2, Alkene = CnH2n
What does it mean if a molecule is saturated or unsaturated? Which group do alkanes and alkenes belong to?
Saturated - only single bonds, alkanes. Unsaturated - at least one double bond, alkenes.
Describe the difference between complete and incomplete combustion
Complete - happens in excess oxygen - produces carbon dioxide and water. Incomplete - happens in limited oxygen - produces carbon monoxide and water
Give the equation for the addition reaction of ethene and bromine. Explain how it is an addition reaction. What observations would be made?
C2H4 + Br2 -> C2H4Br2. It is an addition reaction because the double bond break and hydrogen is added to the molecule(2 reactants to 1 product). Colour change orange to colourless
What is the difference between but-1-ene and but-2-ene?
The double bond is in a different position
Describe and explain the effect of increasing chain length on boiling point
As chain length increases so does the boiling point as the intermolecular forces between molecules become stronger
Name the process by which ethene is produced from crude oil
Cracking
Give the chemical equation for ethene reacting with steam and the conditions of this reaction
C2H4(g) + H2O(g) –> C2H5OH(g) 300oC, 60-70 atm pressure and phosphoric acid catalyst
Give the chemical equation for the fermentation of glucose to produce ethanol. What are the conditions for the reaction
C6H12O6 (Enzymes in yeast) —> 2C2H5OH + 2CO2 30oC, yeast enzyme, no oxygen
What are the advantages and disadvantage of producing ethanol by hydration of steam and fermentation
Hydration - currently inexpensive, continuous process, pure product however uses crude oil a non-renewable source, requires lots of energy due to high T and P. Fermentation - sugar is raw material which is renewable, conditions are inexpensive to produce so little energy required however batch process, slow reaction and impure product
In car engines nitrogen dioxide and nitrogen monoxide can be produced. Give equations for both
N2+2O2 -> 2NO2 N2+O2 -> 2NO
What are the causes, effects and ways of reducing acid rain
Causes: Emissions of SO2, NO2 and NO from burning fossil fuels dissolve in clouds, forming sulfurous, nitrous and nitric acid. Effects: Trees and other vegetation dies. Crops die. Pond life dies due to lowering of pH. CaCO3 is chemically eroded and many metals are corroded. Ways of reducing: Calcium carbonate (limestone) is dissolved in lakes to neutralise acid. Scrubbers are installed in factories to remove S02 from emissions. Catalytic converters in vehicle engines split NO into N2 and O2.
In order, what are the fractions required to be known for the IGCSE EdExcel Chemistry Exam? What are their uses?
• Refinery Gases (domestic heating and cooking) • Gasoline (petrol for cars) • Kerosene ( Jet fuel) • Diesel Oil or gas oil (fuels for large engines - buses, lorries) • Fuel Oil (fuel for ships engines, industrial heating) • Bitumen (resurfacing roads)
How does fractional distillation work?
Crude oil (mixture of hydrocarbons) is heated until it vaporises in a furnace. It is then passed into a fractioning column. The longer chained hydrocarbons have a higher boiling point and remain at the bottom. The opposite is true for the short chained hydrocarbons which rise up the column until they cool and condense. Each ‘fraction’ is siphoned away.
What is the purpose of cracking?
To produce short chain hydroxarbons that are in high demand from long chain hydrocarbons that have a lower demand
Describe the process and conditions of cracking
The sample if heated over a silicon dioxide or aluminium oxide catalyst at around 600-700oC
The products of a particular cracking process are C6H14 and C16H32. What is the formula of the hydrocarbon that was cracked?
C22H46
A hydrocarbon C20H42 is cracked and one product has the formula C12H24. What is the formula of the other compound?
C8H18
What type of reaction is cracking
Thermal Decomposition
What are the uses of the following polymers: poly(ethene), poly(propene), Poly(chloroethene), polytetrafluoro(ethene)
poly(ethene) - milk jugs, detergent bottles, trash bins, plastic bags. poly(propene) - food packaging, ropes, carpets. poly(chloroethene) - Plastic sheets, artificial leather, drainpipes and gutters polytetrafluoro(ethene) - non-stick frying pans
Why are addition polymers hard to dispose of? How is this different to condensation polymers?
They are chemically inert so do not easily break down or biodegrade. Often when they are burned they also produce toxic gases. Some condensation polymers are able to biodegrade, they are known as biopolyesters.
What are the two types of polymerisation? Describe what happens in each
Addition Polymerisation - monomers (often containing double bonds) join together to make a much larger molecule. The double bond breaks and this allow the monomers to form new bonds to other monomer molecules. Condensation Polymerisation - monomers join together and a small molecule (normally water or HCl) is given off
Give two examples of condensation polymers
Polyesters and polyamides (e.g. nylon)
Define the following key terms: homologous series, hydrocarbon, isomerism
Homologous series- a group of compounds with the same functional group, differing by CH2, but with the same general formula, they have similar chemical properties and a trend in physical properties Hydrocarbon - a compound that contains hydrogen and carbon only. Isomer - molecules with the same molecular formula but a different structural formula