TOPIC 6 - ORGANIC

Question 1

what is a hydrocarbon

Answer 1

hydrocarbon is a compound of hydrogen and carbon only

Question 2

what is a homologous series

Answer 2

group of organic compounds with same functional group and general formula

Question 3

what is a functional group

Answer 3

part of molecule that allows you to identify which homologous series its in

Question 4

what are structural isomers

Answer 4

same molecular formula but different structural formula

Question 5

what is stereoisomerism

Answer 5

stereoisomers have same structural formula but different arrangements in space.
1. lack of rotation around the double bond
2. occurs when the two double bonded carbon atoms each have two different atoms or groups attached to them

Question 6

how are alkane fuels obtained from fractional distillation

Answer 6

• crude oil vaporise 350 degrees
• go into fractionating column and rise up (large hydrocarbons dont rise- very high boiling point)
• starts cooling down
  different alkane different chain lengths, different boiling points- condense at different temperatures

Question 7

how are alkane fuels obtained from cracking

Answer 7

heavy fraction (long chain alkanes) broken into smaller hydrocarbons.
- breaks c-c bond

Question 8

what is catalytic cracking

Answer 8

zeolite catalyst (hydrated aluminosilicate), slight pressure, high temp (450 degrees)

Question 9

what is reforming

Answer 9

the processing of straight-chain hydrocarbons into branched-chain alkanes and cyclic hydrocarbons for efficient combustion

Question 10

what pollutants are produced during the process of combustion of alkanes

Answer 10

carbon monoxide, oxides of nitrogen and sulfur, carbon particulates and unburned hydrocarbons

Question 11

problems arising from pollutants from the combustion of fuels

Answer 11

carbon monoxide:
better at binding to haemoglobin in blood than oxygen, so reduces capacity for haemoglobin to carry oxygen, leading to oxygen deprivation- fatal.

sulfur dioxide and oxides of nitrogen:
-burning fossil fuel containing sulfur produce sulfur dioxide when reacting with air, and dissolve with moisture to form sulfuric acid (acid rain.
-oxides of nitrogen are produced when high pressure and temp in car engine cause nitrogen and oxygen to react, dissolve in moisture to form nitric acid.

acid rain destroy vegetation, corrode buildings, kill fish etc.

Question 12

how the use of a catalytic converter solves some problems caused by pollutants

Answer 12

use platinum catalyst

convert harmful gas to less harmful gases.

e.g.
2NO + CO -> N2 + CO2

Question 13

the use of alternative fuels

Answer 13

1. bioethanol
   fermentation of sugar from maize (crops)
2. biodiesel
   refining renewable fats and oils
3. biogas
   breakdown of organic matter

carbon neutral
as the CO2 produced when burnt are absorbed as plants grow.

2 & 3 reduces landfill

Problems:
petrol car machines might need to be modified to use fuels at high ethanol concs.

Also land is now fuel vs food.
-> shortage.

Question 14

what is a radical

Answer 14

a species with an unpaired electron and is represented in mechanisms by a single dot

Question 15

what is homolytic fission

Answer 15

bond breaks evenly, each bonding atom receives one electron from bonded pair

Question 16

the limitations of the use of radical substitution reactions in the synthesis of organic molecules

Answer 16

• you get a mixture of products, not only the desired products - low yield
  (no pure product)
• structural isomers can form, 1-chloropropane, 2-chloropropane.
  e.g.
  when making chloromethane, and theres excess chlorine, hydrogen atoms will be swapped for chlorine atoms.

Question 17

what is the bonding in alkenes in terms of sigma and pi bonds

Answer 17

Pi bonds have high electron density so they’re vulnerable to attack by electrophiles - formed by sideways overlap of 2 p orbitals

Question 18

what is an electrophile

Answer 18

electron pair acceptors

Question 19

how is margarine made

Answer 19

Margarines made by hydrogenating unsaturated vegetable oils- raise melting point so it becomes solid at room temp.

Question 20

potassium manganate, in acid condition to oxidise the double bond of an alkene and produce a diol

Answer 20

shake alkene with acidified potassium dichromate
- purple solution decolourised, oxidised alkene to diol

Question 21

what is heterolytic fission

Answer 21

heterolytic fission
bond breaks unevely with one of the bonded atoms receiving both electrons from bonded pair

Question 22

stability of carbocation

Answer 22

tertiary > secondary > primary

more alkyl groups feed electrons towards the positive charge, carbocation more likely to form

Question 23

know the qualitative test for a C=C double bond using bromine or bromine water

Answer 23

Test c=c bonds.
shake alkene with brown bromine water,

solution decolourise, as dibromoalkane formed

Question 24

why are waste polymers sorted into specific types of polymer

Answer 24

i) recycled by melting and remoulding them (contain non-renewable oil fractions)

some plastics cracked into monomers, can be used as organic feedstock to make more plastics or other chemicals.

ii) waste plastics heated to generate electricity.
-need to be carefully controlled to reduce toxic gases. (PVC burned produced HCl- neutralised with scrubber (base))
or
separate any plastics that will produce toxic gases.

iii)landfill used when:
- hard to separate, costly to separate, difficult to recycle.

Question 25

how chemists limit the problems caused by polymer disposal

Answer 25

i) made from renewable raw materials such as starch (from maize), or oil fractions such as hydrocarbon isoprene. - will not run out - CO2 released will be absorbed when plants grow. - plants based polymers save energy compared to oil based.

Question 26

why double bonds cant rotate

Answer 26

double bonds (p orbitals overlap of pi bonds does not allow rotation- rigid so do not bend much either) however, single bonds can rotate

Question 27

what is a nucleopile

Answer 27

electron pair donor, donates an electron pair to place where electron deficient.

Question 28

what is the trend in reactivity of primary, secondary and tertiary halogenoalkanes

Answer 28

tertiary fastest, secondary then primary carbocation stabilized by three other alkyl groups, inductive effect, most able to donate pair of electrons

Question 29

in terms of bond enthalpy what is the trend in reactivity of chloro-, bromo-, and iodoalkanes

Answer 29

iodoalkanes hydrolysed fastest C-I weakest bond, lowest bond enthalpy, bond break easier, react faster. the larger the halogen, the longer the C-X bond, so lower the bond enthalpy. size of halogen increases down group 7, so iodoalkanes hydrolyse fastest, fluoralkanes hydrolyse slowest- strongest bonds.

Question 30

what happens when you oxidise a tertiary alcohol

Answer 30

does not turn potassium dichromate (VII) orange to green.

Question 31

how does reflux work

Answer 31

use vertical Liebig condenser, continuously boils, evaporates and condenses, avoids naked flames ignite compounds

Question 32

how to extract an organic liquid with a solvent in a separating funnel

Answer 32

if product insoluble, use separation funnel to remove impurities that dissolve in water- salts, water-soluble (alcohol etc) pour the mixture in a separating funnel, add water, shake the funnel separate organic and aqueous layer (immiscible- don't mix) then collect in two different containers.

Question 33

how to distill an organic liquid

Answer 33

gently heating mixture in distillation apparatus, substance will evaporate out the mixture in order of evaporating points. use thermometer if you know boiling point of your pure product, you can know when its condensing. if product: has a lower boiling point than starting material - reaction mixture can be heated so product evaporates from reaction mixture as it forms. has higher boiling point than product, as long as temp is controlled, it will not evaporate out the reaction mixture. Product can react further if left in reaction mixture aldehyde-> carboxylic acid- if product and impurities have different boiling points, distillation can separate them when reach target temp, place flask at open end to collect product.

Question 34

how to prepare a pure sample of an organic liquid with an anhydrous salt

Answer 34

anhydrous magnesium sulfate or calcium chloride (drying agent), bind to water to become hydrated. then filter mixture to remove solid drying agent. if lumpy, add more, then all water will be removed.

Question 35

how to determine boiling point of an organic liquid

Answer 35

when evaporate, its the boiling point, if match data booklet, then pure- no impurities.