ORGANIC I - ALKANES

Question 1

Explain using equations and the intermediate that form in the ozone layer why the EU has banned the use of chlorodifluoromethane as a refrigant

Answer 1

M1 a statement about bond breakage / formation of Cl*
C–Cl / carbon-chlorine bond breakage occurs
OR Cl* / chlorine (free) radical forms
OR correct equation CHClF2 Cl* + CHF2
M2 Cl + O3 –> ClO* + O2
M3 ClO* + O3 –> Cl* + 2O2
M4 CHClF2 / chlorine-containing compounds/ CFCs damage / react with / decrease the ozone layer
ORthis overall decomposi ion occurs; 2O3 3O2ORwithout an ozone layer or with a decreased ozone layer, uv
radiation is not being “filtered” / prevented from passing through the atmosphere or there is a concern about an increase in
skin cancer etc.ORCl* catalyses the decomposi ion of ozone / a single Cl* causes (chain) reac ion / decomposi ion of many
ozone molecules / ozone layeR

Question 2

Define saturated and hydrocarbon

Answer 2

Saturated − single bonds only / no double bonds
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Hydrocarbon − contains carbon and hydrogen (atoms) only

Question 3

Explain why the sulfur compounds found in crude oil should be removed from the fractions before they are used for central heating

Answer 3

(On combustion) SO2 produced
Allow equation to produce SO2. Ignore sulfur oxides.
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Which causes acid rain

Question 4

Suggest one important substance manufactured on a large scale from propene

Answer 4

polypropene / propan(-1 or 2-)ol / propane(-1,2-)diol / isopropanol /
propanone / propanal

Question 5

The petrol fraction from crude oil contains octane (C8H18).
Give an equation for the complete combustion of octane

Answer 5

C8H18 + 12.5 O2 → 8 CO2 + 9 H2O

Question 6

The combustion of petrol in car engines produces the pollutant nitrogen
monoxide.
Give an equation for a reaction that removes nitrogen monoxide in a
catalytic converter.

Answer 6

2 NO + 2 CO → N2 + 2 CO2 or
25 NO + C8H18 → 12.5 N2 + 9 H2O + 8 CO2

Question 7

Some oil-fired heaters use paraffin as a fuel.
One of the compounds in paraffin is the straight-chain alkane, dodecane (C12H26).
(a) Give the name of the substance from which paraffin is obtained.
State the name of the process used to obtain paraffin from this substance.

Answer 7

Crude oil OR petroleum
Not petrol.
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Fractional distillation / fractionation
Not distillation alone.

Question 8

Oxides of nitrogen are also produced during the combustion of paraffin in air.
(i) Explain how these oxides of nitrogen are formed.

Answer 8

M1 Nitrogen and oxygen (from air) react / combine / allow a correct
equation
M2 at high temperatures

Question 9

Explain why the melting point of dodecane is higher than the melting point of
the straight-chain alkane produced by cracking dodecane.

Answer 9

Larger molecule / longer carbon chain / more electrons / larger surface
area
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More / stronger van der Waals’ forces between molecules

Question 10

The alkanes and the alkenes are examples of homologous series of compounds.
One feature of an homologous series is the gradual change in physical properties
as the relative molecular mass increases. State two other general features of an
homologous series of compounds.

Answer 10

Any two from
o chemically similar or chemically the same or react in
the same way
o same functional group
o same general formula
o differ by CH2
(penalise same molecular formula or same empirical
formula)

Question 11

State the physical property of alkenes that allows them to be separated from a
mixture by fractional distillation.

Answer 11

(Different) boiling points

Question 12

State the meaning of the term structural isomerism.

Answer 12

Compound which have the same molecular formula
Accept same no and type of atom for M1
But If same (chemical) formula M1 = 0 but allow M2
If empirical formula CE = 0/2
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but different structures/different structural
formulae/different displayed formulae