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:

Sample A(C6H14)

Sample B(C6H12)

Sample C(C6H12)

Sample D (C6H10)

drops of bromine water

Sample A(C6H14)

Sample B(C6H12)

Sample C(C6H12) (C6H10)

drops of bromine water

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SaturatedNo reactionC6H12C

UnsaturatedDecolourises bromine water

C6H10D

UnsaturatedDecolourises bromine water

C6H12B

SaturatedNo reactionC6H14A

Saturated/ Unsaturated

Reaction with bromine water

Molecular formulaSample

SaturatedNo reactionC6H12C

UnsaturatedDecolourises bromine water

C6H10D

UnsaturatedDecolourises bromine water

C6H12B

SaturatedNo reactionC6H14A

Saturated/ Unsaturated

Reaction with bromine water

Molecular formulaSample

P.P.A. 1. Testing for Unsaturation.

*Safety PrecautionBromine water causes burns and is toxic. If it splashes on your skin, wash it off immediately with sodium thiosulphate. Wear eye protection and gloves.

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P.P.A. 1. Testing for Unsaturation.

C CHH

HCH

CH

CH

HCH

HHH

HH H

Sample A: C6H14

C CHH

HCH

CH

CH

HCH

HHH

HH H

Sample A: C6H14

C CHH

HCH

CH

CH

HCH

HH

HH

Sample B: C6H12

C CHH

HCH

CH

CH

HCH

HH

HH

Sample B: C6H12

CC

CC

C

C

H H

HHHH

HH

HHHH

Sample C: C6H12

CC

CC

C

C

H H

HHHH

HH

HHHH C

C

CC

C

C

H H

HHHH

HH

HHHH

Sample C: C6H12

CC

CC

C

C

H H

H

H

HH

HHHH

Sample D: C6H10

CC

CC

C

C

H H

H

H

HH

HHHH

Sample D: C6H10

ConclusionThe structural formulae of samples A, B, C and D are as follows:

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P.P.A. 2. CrackingCracking is an industrial process in which large alkanes are split into a mixture of smaller useful alkanes and alkenes:

Larger alkane smaller alkane + smaller alkenee.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:

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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.

P.P.A. 2. Cracking

Safety Precautions Bromine solution causes burns and is toxic. Wash off any splashesimmediately 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.

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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)

Half fill a small beaker with water and heat to 40°C.

Add 2 cm3 of blue Benedict’ssolution and heatuntil the waterboils.

Add 3cm3 starch solution and 1cm3

of amylase to a test tube. Place thetest tube in the beaker and leavefor 5 minutes in the warm water.

The blue Benedict’ssolution turns orange/red. This proves thestarch has hydrolysedto a small sugarmolecule.

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P.P.A. 3 Hydrolysis of StarchPart 2 Hydrolysis with an acid (hydrochloric acid)

Add 10 cm3 of starch solution and 1 cm3

of hydrochloric acid to a small beaker. Usinga Bunsen burner heat and boil the mixturefor 5 minutes.

Add *sodium hydrogencarbonate to the mixture. Thiswill produce bubbles of gas. Continue adding sodiumhydrogencarbonate until no more gas is produced.

Add 5cm3 of blue Benedict’s solution and heat the reactionmixture

The blue Benedict’s solution turnsorange/red. This proves starch has hydrolysed to a smaller sugar molecule.

*Sodium hydrogencarbonateneutralises any excess hydrochloric acid

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P.P.A. 4 Effect of Temperature on Rate of Reaction

Beaker with sodium thiosulphateand hydrochloric acid

Paper with a crosson it

The cross will appear to disappear because the reaction mixture will cloud over.

Time how long it takesfor the cross toDisappear.

Repeat the experiment three times increasing the temperature on each occasion.

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AimTo study the effect of varying temperature on the rate of reaction between sodium thiosulphate and hydrochloric acid.

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P.P.A. 4. Effect of Temperature on Rate of Reaction

0.06251648

0.03702739

0.02504032

0.01258020

Rate= 1/t (s-1)

Time (s)

Temperature (°C)

Effect of temperature on rate of reaction

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 20 40 60

Temperature (oC)

Rat

e (s

-1)

Experiment 1

An increase in temperature increases the rate of reaction.

From the graph you may be askedto use.r=1/t or t=1/r

Results

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P.P.A.5. Effect of Concentration on Rate of Reaction

10cm3 of sodium persulphate1cm3 of starch solution

Add 10 cm3 potassium iodide

-Iodine forms from the reaction mixture and turns black in the presence of the starch solution.-Time how long it takes for the black colour to appear.

-This marks the end of the reaction.

-Repeat the experiment changing the concentration of sodium persulphate. This is done by adding water to sodium persulphate.

AimTo study the effect of changing the concentration of sodium persulphateon its rate of reaction with potassium iodide.

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P.P.A. 5. Effect of Concentration on Rate of Reaction Results

Time (s) Rate = 1/t(s-1)

*Vol. Sodium persulphate/Water(cm3)

Experiment no.

1

2

3

4

10/0

8/2

6/4

4/6

54

44

71

107

0.0227

0.0185

0.0141

0.0093

*The concentration of sodium persulphate is altered by adding water in eachexperiment, i.e the sodium persulphate is gradually diluted in each experiment. The total volume, however, is always the same.

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Effect of concentration on rate of reaction

0

0.005

0.01

0.015

0.02

0.025

0 2 4 6 8 10 12

Volume of sodium persulohate

Rat

e (s

-1)

Experiment 1

From the results it can be concluded that the greater the volume (and therefore concentration) of sodium Persulphate, the greater the rate of reaction.

P.P.A. 5. Effect of Concentration on Rate of Reaction Results

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P.P.A.6 ElectrolysisThe following equipment is used to electrolyse certain compounds.

Negative electrode

Positive electrode

Use a solution of copper chloride

A d.c. supply is used so that one electrode remains positive and the other negative. This allows the products to be easily identified.

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 chlorineproduces 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).

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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.

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P.P.A. 7 Preparation of a SaltThe three steps involved are:

Step 2. Filtration of excess metalStep 1. Reaction of Mg + HCl

Step 3. Evaporation of water to leave pure salt Safety note:

1. Acid mists are formed2. Hydrogen is flammable

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P.P.A. 8 Factors which affect voltage

v

Sodium chloridesolution

CopperZinc

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 usedthen different voltages will be obtained.The further apart the metals are in theElectroChemical Series (ECS) the greaterthe voltage obtained.

Electrons flow through the wires and and voltmeter from the higher metal to the lower metal in the ECS: i.e. ZnCu.

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P.P.A. 9 Reaction of metals with oxygen

metalpotassiumpermanganate

Aim: To place different metals in order of reactivity by observing their reaction when heated with oxygen.

Points to note1. Heat metal first then potassium

permanganate.

2. Potassium permanganate providesoxygen.

3. Don’t look too long at burning magnesiumas it releases a very bright light.

4. Don’t use metal in the form of fine powderas the reaction will proceed too quick.

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