Production of Materials

1. Fossil fuels provide both energy and raw materials such as ethylene, for
the production of other substances

. Construct word and balanced formulae equations of chemical reactions
as they are encountered

Gather and present information from first-hand or secondary sources to
write equations to represent all chemical reactions encountered in the HSC
course

. Identify the industrial source of ethylene from the cracking of some
of the fractions from the refining of petroleum

Industrially, ethylene is produced by the cracking [both thermal and
catalytic] of various fractions (usually naptha and LPG) from the refining
of petroleum. These fractions are generally long chain alkanes which are
unreactive. In the cracking process, ethylene is considered a by-product as
the purpose is to produce more quantities of petrol rather than produce
ethylene specifically. In this way ethylene is produced in large
quantities.

Thermal cracking and catalytic cracking are two procedures used to produce
shorter chain hydrocarbons from longer chain hydrocarbons. Thermal cracking
involves high temperatures (450-750C) and pressures (~700kPa) without a
catalyst. Whilst catalytic cracking involves lower temperatures (~500C)
and pressures in the presence of a catalyst (usually zeolites)


. Identify that ethylene, because of the high reactivity of its double
bond, is readily transformed into many useful products

Due to the high electron density of its double bond, ethylene is readily
transformed into many useful products via the addition reaction; where new
atoms are 'added' across the opened up double bond resulting in a saturated
molecule e.g. ethylene + HCl = chloroethane. Ethylene is also used to make
various monomers via the substitution reaction, which can then be used to
make the corresponding polymer, e.g. ethylene into chloroethene into
polychloroethene (PVC).


Identify data, plan and perform a first-hand investigation to compare the
reactivities of appropriate alkenes with the corresponding alkanes in
bromine water [provide a brief summary later]

Aim: To compare the reactivity of hexane with 1-hexene, and cyclohexane
with cyclohexene using bromine water.

Safety: Wear safety glasses. Br water is corrosive (avoid contact and use
droppers, clean up spills immediately). Do not pour any of the liquids down
the drain (collect in organic waste bottle to await disposal by authorised
personnel).

Equipment: cyclohexane, cyclohexene, hexane, 1-hexene, bromine water,
droppers, test tubes, test tube rack, plastic film

Method:
1. Block out all sources of light. (Controlled variable)
2. Place 4 test tubes in test tube rack.
3. Add 4 drops bromine water in 1 test tube. Add 8 drops cyclohexane.
Stopper test tube with plastic film.


4. Shake test tube for 1 minute (Controlled variable). Place back in test
tube rack and allow layers to separate. Record observations (Dependant
variable).
5. Repeat steps 3-4 with cyclohexene, hexane, 1-hexene (Independent
variable-saturation)

Results:
CACWBW = Colour After Contact With Bromine Water
Cyclohexane (Colourless)
-CACWBW: brown/red (a physical reaction; Br dissolving in cyclohexane)
-Decolourises amber bromine water: no
-2 distinct layers
-No chemical reaction

Cyclohexene (Colourless)
-CACWBW: colourless
-Decolourises amber bromine water: yes
-2 distinct layers

[pic](1,2 - dibromocyclohexane)

Hexane (Colourless)
-CACWBW: brown/red (a physical reaction; Br dissolving in hexane)
-Decolourises amber bromine water: no
-2 distinct layers
-No chemical reaction

1- Hexene (Colourless)
-CACWBW: colourless
-Decolourises amber bromine water: yes
-2 distinct layers

C6H12 (l) + Br2 (aq) ( C6H12Br2 (aq) 1,2 - dibromohexane

===================================================================
- Bromine molecules are more soluble in hexane/cyclohexane than water by
the observation that the clear hexane/cyclohexane turned a red/brown
colour when in contact with the amber coloured bromine water, which
also turned a lighter shade of amber. This is due to the non-polar
nature of the bromine which is more soluble in non-polar cyclohexane
and hexane than polar water.
- Alkanes react slowly by the process of substitution
- Alkenes react readily by the process of addition
- In this experiment, a positive reaction is indicated by the bromine
solution turning colourless
- This experiment is destructive as double bonds are broken in a
chemical reaction and products cannot be easily converted back into
reactants.

Controls: Blocking out sources of light (alkanes don't react in the absence
of UV light, with UV light they form free radicals), using the same
equipment, quantities, temperature and degree and period of agitation.

Validity of Method: In distinguishing between alkanes and alkene, the
method is valid so long as it was carried out in the absence of UV light
and results were recorded and compared after a short time interval.

Conclusion: 1-hexene is more reactive than hexane and cyclohexene is more
reactive than cyclohexane. (Alkene is more reactive than the corresponding
alkane)

. Identify that ethylene serves as a monomer from which polymers are
made

Ethylene serves as