other organic chemistry Flashcards
explain what is meant by fractional distillation
separation of compounds by their boiling points
nowadays used catalyst in cracking
what kind of catalyst is it
zeolite
heterogeneous catalyst
products of cracking are mostly
alkenes
understand octane rating
Hydrocarbons used in petrol (gasoline) are given an octane rating which relates to how effectively they perform in the engine. A hydrocarbon with a high octane rating burns more smoothly than one with a low octane rating.
octane rating is higher
in the isomers with branched chains. e.g. octane number of heptane is 0; octane number in 2,2,4-trimethylpentane is 100
isomerisation to increase octane rating condition
Pt catalyst on zeolite, 250 C, 13-30 atm
understand aromatic hydrocarbons
ones based on a benzene ring
how to improve the octane rating of hydrocarbons to be used in petrol
- isomerisation, or 2. reforming
conditions for reforming
a platinum catalyst suspended on aluminium oxide together with various promoters to make the catalyst more efficient. The original molecules are passed as vapours over the solid catalyst at a temperature of about 500°C.
what happens in reforming
Isomerisation reactions occur (as above) but, in addition, chain molecules get converted into rings with the loss of hydrogen.
reforming in hexane draw
hexane gets converted into benzene
http://www.chemguide.co.uk/physical/catalysis/petrochem.html
reforming in heptane draw
heptane gets converted into methylbenzene
http://www.chemguide.co.uk/physical/catalysis/petrochem.html
explain the use of crude oil as a source of both aliphatic and aromatic hydrocarbons
Crude oil is mainly a mixture of chains of carbon atoms. Some of these can be made into rings by a process called reforming, thus it is not only a source of aliphatic hydrocarbons but also of aromatic hydrocarbons
kmno4 solution acidified with dilute h2so4
purple solution becomes colorless
kmno4 solution made slightly alkaline (often by adding na2co3 solution)
the purple solution first becomes dark green solution, due to mno4 2- ions, and then produces a dark brown precipitate, due to solid mno2.
chem eq oxidation of ethene with cold dilute kmno4 solution
name of product
CH2=CH2 + H2O + [O] -> HOCH2CH2OH
ethane-1,2-diol
full ioinic eq oxidation of ethene with cold dilute acidified kmno4 solution
5CH2=CH2 + 2H2O + 2MnO4- + 6H+ -> 5HOCH2CH2OH + 2Mn2+
full ioinic eq oxidation of ethene with cold dilute alkaline kmno4 solution
At first: CH2=CH2 + 2MnO4- + 2OH- -> HOCH2CH2OH + 2MnO42-
But eventually: 3CH2=CH2 +2MnO4- + 4H2O -> 3HOCH2CH2OH + 2MnO2 + 2OH-
full ionic eq oxidation of ethene with cold dilute kmno4 solution
neutral
3CH2=CH2 +2MnO4- + 4H2O -> 3HOCH2CH2OH + 2MnO2 + 2OH-
CH3CH=C(CH3)2 with hot concentrated acidified kmno4 solution produce.. (word and chemical eq)
CH3COOH + CH3COCH3
ethanoic acid + propanone
C4H8: but-1-ene, but-2-ene, 2-methylpropene differences in products with hot concentrated acidified kmno4 solution
CH2=CHCH2CH3 + 5[O] -> CO2 + H2O + CH3CH2COOH
CH3CH=CHCH3 + 2[O] -> 2CH3COOH
CH2C(CH3)2 + 4[O] -> CO2 + H2O + CH3COCH3
describe and explain the inductive effects of alkyl groups on the stability of cations formed during
electrophilic addition
Alkyl groups tend to push electrons away, thus carrying a partial positive charge, and the carbon they are attached to carrying a partial negative charge. The alkyl group has a positive inductive effect.
if a charge is very localized the ion is much less stable than if the charge is spread out over several atoms.
From primary(least stable) to secondary to tertiary(most stable) carbocation, more alkyl groups present places more and more negative charge on the positive carbon, reducing charge density and stabilizing it.
recognise the difficulty of the disposal of poly(alkene)s, i.e. nonbiodegradability and harmful combustion products
the disposal of poly(alkene) plastic waste is difficult, as much of it is chemically inert and non-biodegradable. When burnt, waste plastics may produce toxic products, such as hydrogen chloride from PVC (poly(chloroethene)), dioxins, and toxic CO from incomplete combustion of the hydrocarbons.
Separating other plastic waste from the poly(alkene)s when objects have just been thrown away without being sorted according to their recycle code is another difficulty recycling plants have.
Solutions to the difficulty of the disposal of poly(alkene)s
burn the poly(alkene)s and use the energy released to generate electricity, help conserve our supplies of fossil fuels that currently generate most of our electricity.
Acidic gases would have to be neutralised before releasing the waste gas into the atmosphere and very high temperatures used in incinerators to break down any toxins.
