Cramming Chemistry Paper 2
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General formula (1 mark)
Algebraic formula for a homologous series
Functional group (1 mark)
Group of atoms which when present in different molecules, cause them to have similar chemical properties
Homolytic fission (1 mark)
When a covalent bond breaks and each atom gets one electron
Heterolytic fission (1 mark)
When a covalent bond breaks and one atom gets both electrons
Describe briefly how fractional distillation can be used to convert crude oil into a small number of fractions (6 marks)
• Crude oil is heated and vaporised • It is passed into column • The hydrocarbons condense at different heights • Temperature gradient in column (cooler at the the top) • Larger molecules condense at the bottom of the column • Similar molecules (in terms of size and boiling point) condense together
Thermal Cracking: - Conditions - Main Products (3 marks)
• High temperature (450 degrees) • High pressure (7000kPa) • Mainly alkenes and sometimes hydrogen
Catalytic Cracking: - Conditions - Main Products (5 marks)
Conditions: • Zeolite catalyst • High temperature (450 degrees) • Moderate pressure Main products: • Cyclic alkanes • Aromatic hydrocarbons
Explain how SO₂ can be removed from waste gases in power stations (4 marks)
• Flue gas desulfurisation • Gases passed through scrubber containing basic CaO • Which reacts with SO₂ in a neutralisation reaction: • CaO + SO₂ –> CaSO₃
Environmental consequence of nitrogen oxides (2 marks)
• Toxic - Can form acid rain
Environmental consequence of carbon monoxide (1 mark)
• Poisonous / toxic
Environmental consequence of carbon dioxide (1 mark)
Contributes towards global warming
Environmental consequence of unburnt hydrocarbons (1 mark)
Contributes towards formation of smog
Environmental consequence of soot (2 marks)
• Global dimming - Can lead to respiratory problems
Greenhouse effect (4 marks)
• UV radiation heats surface of Earth • Earth radiates IR radiation • C=O bonds in CO₂ vibrate at similar frequency to IR bonds so C=O absorb IR • Therefore IR does not escape the atmosphere and the atmosphere is warmed
Explain why, even though bromine molecules are non-polar, they react with the double bonds in alkenes (2 marks)
• The electrons of the double bond repel the electron pair in the Br-Br bond • This induces a dipole and so Br₂ becomes polar and electrophilic
Explain how you would distinguish between an alkene and alkane (3 marks)
• Bromine water • Orange to colourless with alkene • Stays orange with alkane
Describe and explain the properties and uses of PVC (4 marks)
• Water proof polymer • Electrical Insulator • Rigid plastic due to strong intermolecular bonding between the polymer chains (therefore, they cannot move over each other) • Used to make window frame coverings and guttering
Describe how PVC can be made more flexible and state the uses of PVC in this form (3 marks)
• Add a plasticiser to weaken the intermolecular forces • Used to make insulation on electrical wires • Used in waterproof clothing
Conditions for formation of carboxylic acid from alcohol (2 marks)
• Excess potassium dichromate - Heat under reflux
Equation for reaction of ethanal with Tollen’s reagent (1 mark)
CH₃CHO + 2Ag⁺ + H₂O –> CH₃COOH + 2Ag + 2H⁺
Equation for reaction of ethanal with Fehling’s solution (1 mark)
CH₃CHO + 2Cu²⁺ + 2H₂O –> CH₃COOH + Cu₂O + 4H⁺
Reagent and condition for hydrogenation of carbonyls (2 marks)
• H₂ + Nickel catalyst - High pressure
Explain why KCN is preferred over NaCN during nucleophilic addition reactions (2 marks)
• HCN is a toxic gas which is difficult to obtain - NaCN is a stronger acid so it will dissociate better than HCN
Describe and explain the uses of esters (4 marks)
• Perfumes + food flavourings as they are sweet smelling • Solvents as they are polar so can dissolve other polar compounds • Glues as they have a low boiling point and can evaporate easily • Plasticisers to make plastics more flexible