AQA A LEVEL CHEMISTRY ORGANIC CHEMISTRY

Relative atomic mass (Ar) - ANSWER Average mass of an atom compared with one twelth of the mass of an atom of carbon 12 Electronegativity - ANSWER Power of an atom to attract the pair of electrons in a covalent bond Standard enthalpy of combustion - ANSWER Enthalpy change when 1 mole of a substance burns completely in oxygen under standard conditions with all reactants and products being in their standard state Standard enthalpy of formation - ANSWER Enthalpy change when 1 mole of a compound is formed from it's elements under standard conditions in their standard states Mean bond enthalpy - ANSWER The average energy needed to break a certain type of bond over a range of compounds Activation energy - ANSWER Minimum energy required for colliding molecules to react Maxwell-Boltzmann distribution x and y axes - ANSWER x: Energy y: fraction/number of molecules What happens to the Maxwell-Boltzmann curve when temperature increases - ANSWER Moves down and to the right Rate of reaction - ANSWER Rate at which product formed/reactant used up Order of reaction - ANSWER Power to which the concentration of a species is raised in the rate equation rearrange k=Ae^-Ea/Rt - ANSWER lnk=-Ea/Rt+lnA Conditions for thermal cracking - ANSWER High temperature and high pressure Products of thermal cracking - ANSWER High % of alkenes Conditions for catalytic cracking - ANSWER High temperature ,slight pressure and in the presence of a zeolite catalyst Products of catalytic cracking - ANSWER Motor fuels and aromatic hydrocarbons Why do we crack alkanes? - ANSWER Smaller alkanes/alkenes generally more useful than longer chain ones Equation for complete combustion of alkanes - ANSWER alkane + oxygen > carbon dioxide + water Equations for incomplete combustion of alkanes - ANSWER alkane + oxygen > carbon monoxide/carbon + water Pollutants produced by combustion engines - ANSWER NOx, CO, C and sunburned hydrocarbons Reaction of methane with chlorine - ANSWER I: Cl2 > 2Cl• P: CH4 + Cl• > CH3• + Chi CH3• + Cl2 > CH3Cl + Cl• T: CH3• + Cl• > CH3Cl 2 equations showing decomposition of the ozone - ANSWER Cl• + O3 > ClO• + O2 ClO• + O3 > 2O2 + Cl• What is a stereospecific active site? - ANSWER An active site that only one enantiomer can fit Developing agents for a chromatogram - ANSWER Ninhydrin or ultraviolet light Method for Thin Layer Chromatography - ANSWER 1) Wearing gloves, draw pencil line 1 cm above bottom of plate 2) Add tiny drop of each solution using capillary tube and dry 3) Add solvent to chamber below pencil line 4) When solvent almost reaches top of plate take it out 5) Dry in fine cupboard then spray with ninhydrin and put in oven 6) Calculate Rf Ho2 to calculate Rf - ANSWER (Distance moved by amino acid) ÷ (Distance moved by solvent) How does cisplatin prevent DNA replication? - ANSWER Ligand substitution forms bond between Platinum and nitrogens from two guanines Test for chloroalkane - ANSWER Warm with silver nitrate gives white ppt of AgCl Test for acyl chloride - ANSWER Warm with silver nitrate gives steamy fumes of Hack and white ppt of AgCl What will NaBH4 reduce? - ANSWER C=O What does hydrogen with a nickel catalyst reduce? - ANSWER C=C What does Sn/HCl reduce? - ANSWER RNO2 to RNH2 What is a dehydrating agent for alcohols to alkenes? - ANSWER heated aluminium oxide What are samples dissolved in for 1H NMR? - ANSWER CCl4 Why is TMS used as a standard? - ANSWER -Chemical shift of 0 (signal far away from anything else) -Inert -Non toxic -Easy to remove from sample (low bp) Describe Thin-Layer Chromatography - ANSWER A plate is coated with a solid and a solvent moves up the plate Describe Column Chromatography - ANSWER A column is packed with a solid and a solvent moves down the column Describe Gas Chromatography - ANSWER A column is packed with a solid or a solid coated by a liquid, and a gas is passed through the column under pressure at high temperature What is the mobile phase? - ANSWER Carries the soluble components of the mixture What relationship between a sample and the mobile phase makes the sample move faster? - ANSWER More soluble components/components with more affinity to the solvent move faster What does the stationary phase do? - ANSWER Holds back components of the mixture that are attracted to it What types of mechanism do haloalkanes undergo? - ANSWER -Nucleophilic substitution by aqueous hydroxide ions, cyanide ions or ammonia -Elimination with ethanolic hydroxide ions What type of mechanism do alkenes undergo? - ANSWER Electrophilic addition by bromine, hydrogen bromide or sulphuric acid Test for primary or secondary alcohols - ANSWER Warm with acidified potassium dichromate (VI) and positive result is Solution turning green Tests for aldehyde or ketone - ANSWER -Warm with Fehlings Solution - brick red precipitate indicates aldehyde -Warm with Tollens reagent (silver nitrate + sodium hydroxide + dilute ammonia) - aldehyde gives a silver mirror Test for alkenes - ANSWER Shake with bromine water- alkene goes from Orange to colourless Test for carboxylic acids - ANSWER Sodium carbonate and effervescence is positive Relative stabilities of carbocations - ANSWER tertiary>secondary>primary What are addition polymers formed from? - ANSWER Alkenes and substituted alkenes Conditions for dehydration of alcohols to give alkenes and water - ANSWER Heat with concentrated sulfuric acid Conditions for production of ethanol by fermentation - ANSWER Yeast, anaerobic, 30-40°C Why are racemic mixtures optically inactive?+ - ANSWER There are equal concentrations of the (+) and (-) isomers What are aldehydes oxidised to? - ANSWER Carboxylic acids What are aldehydes reduced to primary alcohols by and ketones reduced to secondary alcohols by? - ANSWER NaBH4 in aqueous solution Conditions for production of hydroxynitriles from caronyl compounds - ANSWER KCN followed by dilute acid Equations for formation of an ester (acid catalyst) - ANSWER carboxylic acid + alcohol > ester + water acyl chloride + alcohol > ester + HCl Uses of esters - ANSWER Solvents, plasticisers, perfumes and flavourings Products of hydrolysis of vegetable oils/animal fats in alkaline conditions - ANSWER salts of long chain carboxylic acids (soap) and glycerol How is biodiesel produced? - ANSWER Reacting vegetable oils with methanol with a catalyst What type of mechanisms do acyl chlorides and acid anhydrides undergo with water, alcohols, ammonia and primary amines? - ANSWER Nucleophilic addition-elimination Reasons for making aspirin with ethanoic anhydride rather than ethanoyl chloride - ANSWER -Cheaper -Safer (less corrosive) -Doesn't produce dangerous fumes of hydrogen chloride Equation for generation of nitronium ion - ANSWER HNO3 + 2H2SO4 > NO2+ + 2HSO4- + H3O+ Formation of electrophile in acylation - ANSWER AlCl3 + ROCl > RO+ + AlCl4- How can you prepare primary aliphatic amines? - ANSWER -haloalkanes + ammonia -reduction of nitriles Relative base Strength of amines - ANSWER 2°>3°>1°>ammonia>aromatic amines Condensation polymers formed by reactions between: - ANSWER -dicarboxylic acids + diols -dicarboxylic acids + diamines -amines Why can polyesters and polyamides be hydrolysed - ANSWER C=O susceptible to Nucleophilic attack What charge does an amino acid form in acidic solution? - ANSWER Positive What charge does an amino acid form in alkaline solution? - ANSWER Negative What is the relationship between a sample and the stationary phase and what type of bonding is usually involved? - ANSWER More affinity for the stationary phase means that component moves slower, often attracted by hydrogen bonding How are substances separated by chromatography? - ANSWER If suitable stationary/mobile phases are chosen, the balance between affinity for the mobile phase and the stationary phase is different for each component of the mixture. Thus, they move at different rates and are separated over time Why do different substances have different Rf values? - ANSWER More polar bonds mranlobger retention time and smaller Rf value What are the advantages of TLC over paper chromatography? - ANSWER -Runs faster -Smaller amounts of a mixture can be separated -TLC plates are more robust than paper What are the advantages of column chromatography? - ANSWER -More than one solvent can be used which Leads to better separation -Fairly large amounts can be separated What is the main advantage of Gas Chromatography? - ANSWER Very sensitive What is chemical shift? - ANSWER The resonant frequency of the nuclei compared with that of a 1H atom in TMS What kind of environment Leads to a greater chemical shift? - ANSWER A C atom next to a more electronegative atom has a greater chemical shift Summarise what these mean for 13C NMR: 1)Number of signals 2)Chemical shift 3)Area under Peak 4)Splitting - ANSWER 1) One signal for each C environment 2) Greater chemical shift from atoms closer to electronegative atoms or C=C 3) No meaning 4) No splitting for 13C NMR What leads to a lower chemical shift value for H NMR? - ANSWER 1H with more electrons around them/further away fromelectronegative atoms What does the area under the peak represent for 1H NMR? - ANSWER The area under the peak is proportional to the number of 1H atoms represented by the peak What is the n+1 rule? - ANSWER If there are n 1H atoms on the neighbouring carbon then the peak will split into n+1 peaks Why do you try and keep the number of steps as low as possible? (organic synthesis) - ANSWER Improve % yield of final product What is the main oxidizing agent used in organic chemistry? - ANSWER K2Cr2O7/H2SO4 What are primary alcohols oxidised to? - ANSWER Aldehydes then carboxylic acids What are secondaey alcohls oxidised to? - ANSWER Ketones What are the 3 main reducing agents and what dor they reduce? - ANSWER -NaBH4 reduces C=O -H2/Ni reduces C=C -Sn/HCl reduces NO2 to NH2 What are the two main dehydrating agents? - ANSWER -Al2O3 (vapours passed over it) - Acid catalysed elimination by H3PO4 What does a compound being solid indicate? - ANSWER Long C chain or ionic What does a compound being liquid indicate? - ANSWER Medium C chain or polar/hydrogen bonding What does a compound being a gas indicate? - ANSWER Short carbon chain or non-polar bonds What does a smoky flame suggest? - ANSWER High C:H ratio, possibly aromatic In what form do amino acids exist as solids and what does this mean? - ANSWER Zwitterions (ionic lattice) - high melting and boiling points What conditions are needed for hydrolysis of proteins? - ANSWER Conc HCl, reflux What are two examples of secondary structure and how are they held together? - ANSWER Alpha-helix or beta-pleatee sheets and held together by hydrogen bonds How do enzymes increase rate of reaction? - ANSWER Reacting molecules form temporary bonds with enzyme which weakens bonds and lowers Ea Which monomers I terylene made from? - ANSWER Benzene-1,4-dicarboxylic acid and ethane-1,2-diol Which monomers is Nylon-6,6 made from? - ANSWER 1,6-diaminohexane and hexanedioic acid Which monomers is Kevlar made from? - ANSWER 1,4-diaminobenzene and benzene-1,4-dicarboxylic acid How do you name amines? - ANSWER -amine or amino- Is phenylamine soluble? - ANSWER Not very because of non-polarity of benzene ring cannot form hydrogen bonds How could you regenerate a soluble amine from the ammonium salt? - ANSWER Add strong base such as NaOH What inductive effect do alkyl groups have? - ANSWER Positive - increase electron density around N to make it a stronger base What inductive effect do aryl groups have? - ANSWER Negative - decrease electron density around N to make it a weaker base What are tertiary amines never good bases? - ANSWER Insoluble in water How would you maximise yield of primary amine? - ANSWER Excess ammonia Why is benzene not used in schools? - ANSWER Its a carcinogen How do youn name compounds contating a benzene ring? - ANSWER Phenyl- or -benzene How do subtsituents with a positive inductive effect (alkyl groups) affect further substitution? - ANSWER Release electrons into ring making substitutions to 2,4,6 More likely How do subtsituents with a negative inductive effect (NH2) affect further substitution? - ANSWER Remove electrons from ring making reactions slower and directing subtsituents to 3,5 What catalyst is needed for formation of esters from alcohols and carboxylic acids? (and hydrolysis) - ANSWER Conc H2SO4 What are the conditions for making glycerol? - ANSWER NaOH and 60°C When purifying by recrystallisation, why is the minimum volume of hot solvent used? - ANSWER So that saturated solution is created - as many crystals will fall out of solution as possible when cooled Why is the solution filtered hot when purifying by recrystallisation? - ANSWER To remove insoluble impurities Why is the solution cooled in an ice bath when purifying by recrystallisation? - ANSWER To endure as many crystals fall out of solution as possible - higher yield Why are crystals washed with cold water when purifying by recrystallisation? - ANSWER To remove soluble impurities How would you separate the crystals from the reaction mixture when purifying by recrystallisation? - ANSWER Filter under reduced pressure using a Buchner funnel What is the first stage in the synthesis of lactic acid from ethanal? - ANSWER CH3CHO + KCN > CH3CH(OH)CN What is the second stage in the synthesis of lactic acid from ethanal? - ANSWER CH3CH(OH)CN + HCl + 2H2O > CH3CH(OH) COOH + NH4Cl What is the functional group of an alcohol? - ANSWER -OH (hydroxyl group) What is the functional group of a carboxylic acid? - ANSWER -COOH (carboxyl group) What is the functional group of an alkene? - ANSWER C=C What is the empirical formula? - ANSWER The simplest whole number ratio of atoms of each element in a compound What is a homologous series? - ANSWER Family of organic compounds that have the same functional group and the same general formula What is the general formula for alkanes? - ANSWER Cn H2n+2 What is a haloalkane? - ANSWER An alkane with at least one halogen atom in place of a hydrogen atom What is a cycloalkane? - ANSWER cyclic hydrocarbon with only single bonds What is the general formula for cycloalkane? - ANSWER CnH2n What is the side chain length for methyl? - ANSWER 1 What is the side chain length for ethyl? - ANSWER 2 What is the side chain length for propyl? - ANSWER 3 What is the side chain length for butyl? - ANSWER 4 What is the side chain length for pentyl ? - ANSWER 5 What is the side chain length for hexyl? - ANSWER 6 What is the general formula for alkenes? - ANSWER CnH2n What is an aldehyde? - ANSWER O=C-H at the end of a molecule What is a ketone? - ANSWER C=O in middle of chain What is an advantage of the IUPAC naming system? - ANSWER Scientific ideas can be communicated across the globe What does a curly arrow represent in mechanisms? - ANSWER Movement of an electron pair Why does Na+ in NaCl not feature in the equation? - ANSWER Because NaCl dissociates What are structural isomers? - ANSWER Compounds with the same molecular formula but different structural formula What are the 3 structural isomers? - ANSWER - chain isomers - position isomers - functional group isomers What are chain isomers? - ANSWER Compounds with the same molecular formula but different arrangements of the carbon skeleton What are position isomers? - ANSWER Same skeleton and same atoms or groups of atoms attached. But atoms or groups of atoms are attached to different carbon atoms What are functional group isomers? - ANSWER Same atoms arranged into different functional groups What are steroisomers? - ANSWER Molecules with the same structural formula but a different spatial arrangement of atoms What molecules have restricted rotation? - ANSWER C=C bonds How can you identify an E-Z isomer? - ANSWER E - matching groups on opposite sides Z - groups are on the same side What are the Cahn-prolog priority rules? - ANSWER - atom with the higher atomic number on each carbon is given higher priority What are the 3 types of isomers? - ANSWER 1. chain isomers : straight chain / branched chain 2. positional isomers : same skeleton, same atoms just different placement of the atom (to a carbon atom) 3. functional group isomers : different functional groups (eg. branched -> cycloalkanes) What are stereoisomers? - ANSWER same structural formula but different arrangement in space Differences between a 'Z' and 'E' isomer? - ANSWER 'Z' -> zame zide 'E' -> diff side How does fractional distillation work? - ANSWER 1. oil is heated and vaporised 2. passed into column 3. fractions condense at different heights 4. temperature of the column decreases moving upwards 5. seperation depends on boiling points 6. higher boiling point hydrocarbons condense at the top 7. b.p. depends on size of molecules= the larger the molecule the larger the VDWs forces 8. similar molecules (b.p. , mass , size) condense together List the fractions from shortest to longest hydrocarbon chain lengths. - ANSWER 1. gases 2. petrol (gasoline) 3. naphtha 4. kerosene (paraffin) 5. gas oil (diesel) 6. mineral oil (lubricating) 7. residue (fuel oil, wax/grease & bitumen) GREAT PENGUINS NEVER KEEP GOING MISSING REGULARLY Requirements for thermal cracking : - ANSWER - high temperatures (400-900degrees C) - high pressure (7000kPa) - produces a lot of alkenes (useful when making plastics) Requirements for catalytic cracking : - ANSWER - Slight pressure (2atm) - High temperature (450 degrees C) - Zeolite catalyst - Aromatic hydrocarbons & branced / cyclic alkanes formed -> used to make MOTOR FUELS products of complete combustion - ANSWER water and carbon dioxide products of incomplete combustion : - ANSWER carbon monoxide & water and... Carbon (soot) How to remove CO? - ANSWER catalytic converters How are oxides of nitrogen formed? - ANSWER when N2 in the air reacts in the engines of cars at high temperatures and the spark. Equation of the oxidation of CO... - ANSWER 2CO + O2 -> 2CO2 Equation of the reduction of NO - ANSWER 2CO + 2NO -> 2CO2 + N2 Equation of oxidation of unburnt hydrocarbons - ANSWER CnH2n+2 + (3n+1)[O] → nCO2 + (n+1)H2O How are VOCs formed? - ANSWER unburnt hydrocarbons from fuels and their oxides formed in car engines. How is PAN formed? - ANSWER nitrogen oxides reacting with VOCs How to remove sulfur dioxide? - ANSWER [FLUE GAS DESULPHURISATION] powdered calcium carbonate / calcium oxide is mixed with water to make an alkaline slurry, when flue gases mix with alkaline slurry, the acidic sulfur dioxide gas reacts with calcium compounds to form a harmless salt. how does the greenhouse effect work? - ANSWER UV radiation passes through the atmosphere and into the Earth's surface and heats up the earth. The earth will then radiate out the infrared long wavelength, however due to the presence of greenhouse gases (such as CO2), the bonds in CO2 absorbs the radiation- causing the earth to warm. Test for alkenes : - ANSWER [Addition Reaction] : Add bromine water to solution and shake, if alkene is present, solution will turn colorless What is an electrophile? - ANSWER a species which is electron deficient and can accept a pair of electrons to form a covalent bond. Why are major products often formed? - ANSWER major products are formed via the most stable carbocations (ones which are attached to the most number of alkyl groups) addition polymers - ANSWER repeating units - ANSWER role of plasticizers - ANSWER makes PVC flexible. 1. used for flooring 2. used for the insulation of electrical cables how do plasticizers make PVC soft? - ANSWER plasticizers will be put between alkane chains (London forces) causing the IMF to weaken. how to form alkenes - ANSWER alcohols undergo dehydration to form alkenes (eliminating water) - this is renewable how to carry out distillation of alcohols? - ANSWER step 1 : distillation 1) add H2SO4 to a round bottom flask containing cyclohexanol. mix and add 2-3 boiling chips (helps the reaction boil calmly) 2) heat around 83 degrees celsius using a water bath / electric heater. 3) chemicals with a boiling point of 83 degrees will evaporate and rise, moving into the condenser where cool water will be flowing pass to turn the gas into a liquid. step 2: 1) the product collected at the end will be impure. 2) put it into a separating funnel and add water to dissolve water soluble impurities, thus creating an aqeous solution. 3) allow the mixture to seperate into layers, drain off the bottom (containing impurities) step 3: 1) drain the cyclohexene into a round bottom flask. 2) add anhydrous calcium chloride, and let the mixture dry for about 20 minutes) 3) distill one more time how can we produce alcohols? - ANSWER via hydration of alkenes (electrophilic addition) what are the conditions required for hydration of alkenes? - ANSWER - 300 degrees celsius - pressure of 60atm - phosphoric acid catalyst what is another way to produce alkenes? - ANSWER fermentation explain fermentation - ANSWER -> fermentation is an exothermic process, requiring yeast -> sugar is dissolved in water, yeast is added... -> yeast produces an enzyme which converts glucose into ethanol and carbon dioxide -> once ethanol is formed, it undergoes fractional distillation to seperate it from the rest.