Cramming Chemistry Paper 2 Flashcards
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
State what fats and oils are composed of (2 marks)
- Glycerol
- Long chain carboxylic acids
Draw the structure of glycerol (1 mark)
Propane- 1,2,3 - triol
Describe what biodiesel is (1 mark)
Mixture of methyl esters of long chain carboxylic acids
Describe how biodiesel can be formed (2 marks)
- Vegetable oils + 3 methanol
- Presence of strong alkali catalyst
Explain why benzene is described as planar (2 marks)
- C-C bonds are the same
- Bond length is intermediate between a single bond and double bond
Explain why substitution reactions are preferred over addition reactions in aromatic compounds (2 marks)
- Addition reactions would involve breaking up the delocalised system
- Therefore as aromatic compounds have high electron density, they attract electrophiles and undergo electrophilic substitution
Explain why the nitration of benzene is important (3 marks)
Useful in the synthesis of:
- TNT
- Explosives
- Amines (which are used to make dyes)
Explain why Friedel crafts acylation is an important step in synthesis (1 marks)
- This reaction introduces a reactive functional group on to the benzene ring so many other reactions can occur
State two disadvantages of preparing amines from nitriles (2 marks)
- KCN is toxic
- 2 step reaction so may have low yield
Reagent for reduction of nitriles (1 marks)
- LiAlH₄ in ether
OR - H₂ and nickel catalyst
Reagent for reduction of nitroarenes (1 mark)
Sn + HCl
OR
Fe + HCl
Explain why poly(alkenes) are inert (1 mark)
- C-C and C-H bonds are strong
State the uses of Terylene (1 mark)
- Clothing fabric
- Tire cords
State the use of nylon (1 mark)
- Clothing fabric
State the use of Kevlar (1 mark)
Bulletproof clothing
Disadvantages of disposing plastics via landfill (4 marks)
Disadvantages:
- Over time, the waste will decompose, producing greenhouse gases
- Waste gases can leach into water and contaminate water
- A lot of land is wasted
- Most polymers take years to break down
Advantages and disadvantages of disposing plastics via incineration (4 marks)
Advantages:
- Energy produced whilst burning the rubbish can be used to generate electricity
- Doesn’t waste land space (volume of rubbish is greatly reduced
Disadvantages:
- Some toxins can be released
- CO₂ and other greenhouse gases are released
Advantages and disadvantages of recycling polymers (4 marks)
Advantages:
- Saves raw materials
- Cheaper to recycle plastics than to make them from scratch
- Less CO₂ is produced when recycling plastics than when incinerating them
- Reduces the reliance of landfill
- Some plastics can be remoulded into other plastics
Disadvantages:
- Plastics are often contaminated with other materials
- Separation of the different types of plastics is expensive and time consuming
Explain why amino acids have a high melting point (2 marks)
- Amino acids exist as dipolar zwitterions
- So there is ionic interaction between them which requires a lot of energy to be overcome
Describe the alpha helix secondary structure of a protein (2 marks)
- 3D arrangement of amino acids with polypeptide chain in a corkscrew shape help by hydrogen bonds
- R groups face the outside
Describe the beta-pleated sheet secondary structure of a protein (2 marks)
- Protein chain folds into parallel strands side by side
- Held together by hydrogen bonds
Describe the tertiary structure of proteins (2 marks)
- Folding of secondary structure into a more complex shape
- Held in place by interactions such as ionic, disulfide and hydrogen bonds between the R-side groups
Explain how cisplatin prevents DNA replication in cancer cells (2 marks)
- Ligand replacement reaction with DNA
- Dative covalent bond is formed between platinum and a nitrogen atom on guanine
Explain why CCl₄ and CDCl₃ are good solvents to use in NMR spectroscopy (2 marks)
- Inert
- No H atoms so no peaks
State the use of TMS in H NMR spectroscopy and explain how its properties are suitable for this use (4 marks)
- Used to calibrate the spectrum
- Only gives one signal away from all the other signals
- Non-toxic and inert
- Low boiling point so can be removed from the sample easily
Explain what determines the separation of molecules in chromatography (1 mark)
Balance between solubility in the moving phase and retention by the stationary phase
Describe TLC (2 marks)
- Plate coated with solid
- Solvent moves up the plate
Describe column chromatography (2 marks)
- Column packed with a solid
- Solvent moves down the column
Describe gas chromatography (2 marks)
- Column packed with a solid or with a solid coated by a liquid
- And gas (e.g. nitrogen, helium, argon) is passed through the column under high pressure at a high temperature
Outline the process of column chromatography (5 marks)
- A cotton wool is placed in the tube to retain the solid in the tube
- Glass tube is filled with a slurry formed from the stationary phase (silica) and the solvent
- The mixture to be analysed is dissolved in a minimum amount of solvent and added to the column
- The solvent is then run through the column and the molecules in the mixture start to separate
- The time for each component in the mixture to reach the end of the column is recorded (retention time)
Mobile and stationary phase in gas-liquid chromatography (2 marks)
- Mobile: inert gas, e.g. helium (so that it doesn’t react with the components being separated)
- Stationary: high boiling point liquid absorbed onto a solid
Retention time in gas-liquid chromatography (1 mark)
Time taken for a particular compound to travel from the injection of the sample to where it leaves the column in the detector
Factors which influence retention time in gas-liquid chromatography (3 marks)
- Column temperature
- Column length
- Flow rate
State two uses of gas-liquid column chromatography in conjunction with mass spectroscopy (2 marks)
- Forensics
- Airport security
x and y axis of Maxwell Boltzmann curve
x: collision energy
y: fraction of molecules with energy
Suggest how a reaction goes to completion even if only a few particles have energy greater than Ea (1 mark)
Particles gain energy through collisions
Describe how the Maxwell-Boltzmann curve changes when concentration/pressure are increased (2 marks)
- Curves will be higher as more particles present
- But overall shape is the same
State and explain the stability of benzene compared with the hypothetical cyclohexatriene (4 marks)
- Benzene is more stable than cyclohexatriene
- Expected ΔH hydrogenation of C₆H₆ is 3(–120)
- Actual ΔH hydrogenation of benzene is 152 kJ mol-1 (less exothermic)
- Because of delocalisation / electrons spread out
Explain why cyclohexa-1,3-diene is more stable than cyclohexa-1,4-diene (3 marks)
- Proximity − for 1,3 C=C bonds are closer together
- Some overlap of electrons, π clouds or p orbitals
- So extra stability for the 1,3- isomer
State the reagents for the conversion of benzene into cyclohexane (1 mark)
Ni + H₂
Explain the bonding in and the shape of a benzene molecule. Compare the stability of benzene with that of the hypothetical cyclohexa-1,3,5-triene molecule (6 marks)
Bonding:
- Each C has three (covalent) bonds
- Spare electrons (in a p orbital) overlap (to form a cloud)
- Delocalisation
Shape:
- Planar
- Hexagon/6 carbon ring/120 bond angle
- C–C bonds equal in length / C–C bond lengths between single and double bond
Stability:
- Expected △H of cyclohexatriene = –360 kJ mol–1
- △H of benzene (is less exothermic) by 152 kJ mol–1
- Benzene lower in energy than cyclohexatriene / Benzene is more stable
