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P.P.A. 1. Testing for Unsaturation
The presence of unsaturation in organic compounds can be shown using bromine
water. When bromine water is shaken with an unsaturated hydrocarbon the
reaction mixture turns colourless. The unsaturated hydrocarbon is said to
decolourise the bromine water. When a saturated hydrocarbon and bromine
water are mixed the orange/red colour of the bromine water remains.
The aim of this experiment is to test for unsaturation in four different
hydrocarbons:
drops of bromine water
Sample A
(C 6H 14 )
Sample B
(C 6H 12 )
Sample C
(C 6H 12 )
Sample D
(C 6H 10 )
Saint Ninian’s High School Chemistry Department
P.P.A. 1. Testing for Unsaturation.
Sample Molecular formula Reaction with
bromine water
SNHS
Saturated/
Unsaturated
A
C6H14
No reaction
Saturated
B
C6H12
Decolourises
bromine water
Unsaturated
C
C6H12
No reaction
Saturated
D
C6H10
Decolourises
bromine water
Unsaturated
*Safety Precaution
Bromine water causes burns and is toxic. If it splashes on your skin,
wash it off immediately with sodium thiosulphate. Wear eye protection
and gloves.
Saint Ninian’s High School Chemistry Department
SNHS
P.P.A. 1. Testing for Unsaturation.
Conclusion
The structural formulae of samples A, B, C and D are as follows:
Sample A: C6H14
H H H H H H
H C C C C C C H
H H H H H H
Sample B: C6H12
H
H H H
H C C C C C C H
H H H H H H
Sample C: C6H12
H H
C
H
H
C
C
H
H
H
C
C H
H
H
C
H
H
Sample D: C6H10
H H
C
H
C H
H C
H
C
C H
H
C
H
H
P.P.A. 2. Cracking
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Cracking is an industrial process in which large alkanes are split into a
mixture of smaller useful alkanes and alkenes:
Larger alkane  smaller alkane + smaller alkene
e.g. C10H22  C8H18 + C2H4
Cracking is important because it produces smaller chain hydrocarbons for which there
is a greater demand. Secondly, it produces unsaturated hydrocarbons, which are
important starting materials in the manufacture of plastics.
The set up for the experiment is as follows:
Saint Ninian’s High School Chemistry Department
P.P.A. 2. Cracking
SNHS
The aluminium oxide catalyst is heated firstly. The heat is then passed to the
plug of wool soaked in paraffin (a mixture of alkanes of chain length C20 and
greater). To demonstrate that some of the products are unsaturated there is a
test tube with bromine solution. This will be decolourised when the unsaturated
product mixes with it.
Safety Precautions
Bromine solution causes burns and is toxic. Wash off any splashes
immediately with sodium thiosulphate. There is a danger of suck-back
in this experiment. Remove the boiling tube from the test-tube of bromine
solution and stop heating if you think there is suck-back.
Saint Ninian’s High School Chemistry Department
SNHS
P.P.A. 3 Hydrolysis of Starch
Aim: To hydrolyse starch in the presence of an enzyme and an acid.
Part 1 Hydrolysis with an enzyme (amylase)
3
Half fill a small beaker with water
and heat to 40°C.
3cm3
1cm3
Add
starch solution and
of amylase to a test tube. Place the
test tube in the beaker and leave
for 5 minutes in the warm water.
Add 2 cm of
blue Benedict’s
solution and heat
until the water
boils.
The blue Benedict’s
solution turns orange/
red. This proves the
starch has hydrolysed
to a small sugar
molecule.
Saint Ninian’s High School Chemistry Department
SNHS
P.P.A. 3 Hydrolysis of Starch
Part 2 Hydrolysis with an acid (hydrochloric acid)
Add 10 cm3 of starch solution and 1 cm3
of hydrochloric acid to a small beaker. Using
a Bunsen burner heat and boil the mixture
for 5 minutes.
*Sodium hydrogencarbonate
neutralises any excess
hydrochloric acid
Add *sodium hydrogencarbonate to the mixture. This
will produce bubbles of gas. Continue adding sodium
hydrogencarbonate until no more gas is produced.
Add 5cm3 of blue Benedict’s
solution and heat the reaction
mixture
The blue Benedict’s solution turns
orange/red. This proves starch has
hydrolysed to a smaller sugar molecule.
Saint Ninian’s High School Chemistry Department
P.P.A. 4 Effect of Temperature
on Rate of Reaction
SNHS
Aim
To study the effect of varying temperature on the rate of reaction
between sodium thiosulphate and hydrochloric acid.
Beaker with sodium thiosulphate
and hydrochloric acid
The cross will appear to
disappear because the
reaction mixture will
cloud over.
Paper with a cross
on it
Time how long it takes
for the cross to
Disappear.
Repeat the experiment three times increasing the temperature on
each occasion.
Saint Ninian’s High School Chemistry
Department
P.P.A. 4. Effect of Temperature
on Rate of Reaction
SNHS
Results
Temperature
(°C)
Time
(s)
Effect of temperature on rate of reaction
Rate= 1/t
(s-1)
0.07
0.06
80
0.0125
32
40
0.0250
39
27
0.0370
0.05
Rate (s-1)
20
0.04
Experiment 1
0.03
0.02
0.01
48
16
0.0625
0
0
20
40
60
Temperature (oC)
An increase in temperature
increases the rate of reaction.
From the graph you may be asked
to use.
r=1/t or t=1/r
Saint Ninian’s High School Chemistry Department
P.P.A.5. Effect of Concentration
on Rate of Reaction
SNHS
Aim
To study the effect of changing the concentration of sodium persulphate
on its rate of reaction with potassium iodide.
Add 10 cm3 potassium iodide
10cm3 of sodium persulphate
1cm3 of starch solution
-Iodine forms from the reaction mixture and turns black in the presence of
the starch solution.
-Time
-This
how long it takes for the black colour to appear.
marks the end of the reaction.
-Repeat the experiment changing the concentration of sodium persulphate. This is
done by adding water to sodium persulphate.
Saint Ninian’s High School Chemistry Department
P.P.A. 5. Effect of Concentration
on Rate of Reaction Results
Experiment
no.
*Vol. Sodium persulphate/Water
(cm3)
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Time (s)
Rate = 1/t
(s-1)
1
10/0
44
0.0227
2
8/2
54
0.0185
3
6/4
71
0.0141
4
4/6
107
0.0093
*The concentration of sodium persulphate is altered by adding water in each
experiment, i.e the sodium persulphate is gradually diluted in each experiment.
The total volume, however, is always the same.
Saint Ninian’s High School Chemistry Department
P.P.A. 5. Effect of Concentration
on Rate of Reaction Results
SNHS
Effect of concentration on rate of reaction
0.025
Rate (s-1)
0.02
0.015
Experiment 1
0.01
0.005
0
0
2
4
6
8
10
12
Volume of sodium persulohate
From the results it can be concluded that the greater
the volume (and therefore concentration) of sodium
Persulphate, the greater the rate of reaction.
Saint Ninian’s High School Chemistry Department
P.P.A.6 Electrolysis
SNHS
The following equipment is used to electrolyse certain compounds.
A d.c. supply is used so that one electrode remains positive and the other
negative. This allows the products to be easily identified.
Positive
electrode
Negative
electrode
Use a solution of copper chloride
Copper is formed as a brown solid at the negative electrode.
A piece of litmus paper is held above the positive electrode to show that chlorine
produces an acidic solution. The litmus paper is bleached by the chlorine. Moreover,
chlorine gas can also be detected at the negative electrode by its distinctive smell
(similar to a swimming pool or bleach).
Saint Ninian’s High School Chemistry Department
SNHS
P.P.A. 7 Preparation of a Salt
The aim of the experiment is to prepare a pure sample of a
soluble salt such as magnesium sulphate.
Magnesium is added to dilute hydrochloric acid until no further
evolution of hydrogen gas, this marks the end of the reaction.
The excess magnesium is filtered off and some of the water is
evaporated from the salt solution.
The hot solution is set aside to crystallise.
The same method can be used to prepare an insoluble
salt (precipitate).
A metal carbonate can also be used. This will produce
carbon dioxide gas.
Saint Ninian’s High School Chemistry Department
P.P.A. 7 Preparation of a Salt
SNHS
The three steps involved are:
Step 1. Reaction of Mg + HCl
Step 3. Evaporation of water to leave
pure salt
Step 2. Filtration of excess metal
Safety note:
1. Acid mists are formed
2. Hydrogen is flammable
Saint Ninian’s High School Chemistry Department
SNHS
P.P.A. 8 Factors which affect voltage
Aim: To investigate a factor which might affect the size of voltage produced
by a simple cell.
Factors that may be investigated:
-use different pairs of metals
-change type of electrolyte
-change concentration of electrolyte
If different pairs of metals are used
then different voltages will be obtained.
The further apart the metals are in the
ElectroChemical Series (ECS) the greater
the voltage obtained.
v
Zinc
Copper
Sodium chloride
solution
Electrons flow through the wires and
and voltmeter from the higher metal to
the lower metal in the ECS:
i.e. ZnCu.
Saint Ninian’s High School Chemistry Department
P.P.A. 9 Reaction of metals with oxygen
SNHS
Aim: To place different metals in order of reactivity by observing their reaction when
heated with oxygen.
Points to note
1. Heat metal first then potassium
permanganate.
potassium
permanganate
2. Potassium permanganate provides
oxygen.
metal
3. Don’t look too long at burning magnesium
as it releases a very bright light.
4. Don’t use metal in the form of fine powder
as the reaction will proceed too quick.
Saint Ninian’s High School Chemistry Department