answers to learn F335

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Flashcards on answers to learn F335, created by joannalivesey on 25/05/2014.
joannalivesey
Flashcards by joannalivesey, updated more than 1 year ago
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Created by joannalivesey almost 10 years ago
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Question Answer
Problems with working at high pressure • danger of explosions • expensive: lots of energy needed to run compressor/ thick walls of the specialised plant are expensive
Ionic properties • high melting point- strong electrostatic forces between neg and pos ions •dissolves in water- ions are hydrated, they form ion-dipole bonds with water •conducts electricity when in solution/molten - free ions can MOVE
Raw and feedstock materials for haber process • raw: air and natural gas • feedstock: nitrogen and hydrogen
Why is ammonium nitrate a good fertiliser? • High % nitrogen - nitrogen needed by plants to make proteins etc • Soluble • NH4+ held by clay in the soil
Uses of nitric acid • Making fertilizers • Making dyes • Making explosives
Effect of temp on rate • molecules have more KE so collide more frequently • With energy greater than activation enthalpy
Why use a high-ish temp if forward reaction is exothermic? Compromise between rate and yield
Problems with NO(g) • toxic (respiratory problems) • gives rise to acid rain • photochemical smog • greenhouse gas
Why is nitrogen hard to fix? • Nitrogen is very unreactive with a high Ea • Strong triple bond between the N atoms that needs a lot of energy to break
Explain the circle in a benzene ring • delocalised electrons • one electron from each carbon • two rings of electrons • above and below carbon ring
Why are azo compounds coloured? • Presence of a chromophore- an extended delocalised system • Compound absorbs in the visible region • Complementary colour to the one absorbed gets transmitted (what we see)
What is meant by ‘delocalisation’? • Electrons are not associated with one bond • Instead, they are spread over several atoms (NOT whole molecule!)
Effect of increasing length of chromophore of a molecule • Decreases the frequency of light absorbed • Lower excitation energy • smaller distance between energy levels (E=hv) • greater intensity of absorption
Conditions for Haber process 450 ˚C, 200 atm, iron catalyst
Causes of acid rain • power stations • burning of fuels containing sulfur • NOx produced in high T+P of car engines
Problems of acid rain • attacks buildings • damages trees/plants • damages/kills fish • causes respiratory problems
What is standard enthalpy change of formation? enthalpy change when one mole of the compound is formed from its elements under standard conditions, and with everything in its standard state
Why is benzene colourless? stable molecule so absorbs in UV region (higher frequency than visible)
What is the SO3- functional group called? Why does it increase solubility of an azo dye? • sulfonate • ions are readily hydrated by water molecules
how do buffers work? • Maintain a constant pH despite small additions of acid or alkali • Acid is H+, alkali is OH- • (on adding acid) equilibrium moves to left to remove H+ • (on adding alkali) equilibrium moves to right and forms H+ to neutralise OH- • Because [salt] and [acid] are large, pH remains constant
How can impurities poison a catalyst? • Impurity binds to catalyst surface • prevents reactants adsorbing to catalyst surface
How could you alter the colour of something with a chromophore? • Add functional group; e.g. NH2, OH, to change the conjugation • Add more double bonds; to extend the conjugated system • Change position of side chains around a benzene ring; e.g. to 1:2 or 1:3 • Change configuration of C=C; to make the cis/trans form
why is Al3+ more hydrated than Na+? • higher CHARGE DENSITY (larger core charge and smaller ionic radii) • attracts more water molecules
Describe the chlorination of benzene mechanism • AlCl3 further polarises C-Cl bond to create Cl+ and AlCl4- • the Cl+ acts as an electrophile and attacks the benzene • H+ is released from the benzene and AlC3 is reformed (H+ + AlCl4- -> HCl + AlCl3)
why does benzene undergoes substitution reactions, rather than addition reactions? • benzene has a delocalised system of electrons which makes it stable • delocalisation is retained in substitution reactions (so stability is retained) • addition product is less stable as delocalisation is lost
why convert a compound into a salt to be used as the herbicide? much more soluble
why does increasing pressure increase rate? • molecules in smaller volume • more frequent collisions
talking about reflectance spectrums (e.g. if compound is blue) • reflects only blue • absorbs all other colours
why is oleic acid insoluble in water? • hydrogen bonds are broken in water • id-id bonds are broken in oleic acid • id-id bonds are made between oleic acid and water • more energy required to break bonds than make them
weak acid assumptions • [H+] = [A–] (all H+ comes from acid) • initial [HA] = equilibrium [HA]
difference between co-product and by-product • co-product is formed in the reaction that produces the main product  • by-product is formed by side/unwanted reactions
advantages of a high atom economy? little waste as most atoms used
what is a pharmacophore? part of the molecule that is responsible for the medicinal action (e.g. binds to an active site)
WHAT DO YOU NEED TO GO OVER AND CHECK?????? - SIGNS OF ENTHAPLY/ENTROPY STUFF - IF ARROWS SHOULD BE DRAWN AS EQUILIBRIUM ARROWS OR NORMAL ONES!!!
why will diazonium salts not react with benzene, only phenol/phenyl amine? The diazonium salt is a relatively weak electrophile and will only react with particularly electron-rich activated benzene rings
why is CO2 not polar? • dipoles cancel • centre of negative charge is on the centre of positive charge
sequence of events from plant fungus to drug • show that a compound has medicinal properties • clinical trials • identify pharmacophore •synthesise similar molecules
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