Alkane and Alkene Reaction With Br Water(Chemistry)

Reaction of Alkanes and Alkenes with Bromine Water AIM: To determine the difference between the reactivity of alkanes and alkenes. MATERIALS:       

Bromine water Pure cyclohexane Pure cyclohexene Molecular model kits Test tubes Measuring cylinders Beakers

DISPOSAL: Place in an organic waste bottle, rinse the test tube and place rinse in an organic waste bottle RISK ASSESSMENT: Chemical Bromine Water

Risk Not Hazardous according to Worksafe Critieria, should not be ingested

Cyclohexane

Toxic by all routes of exposure, highly flammable and vapour moderately toxic

Cyclohexene

Toxic by all routes of exposure, highly flammable and vapour moderately toxic

Management Use eye and skin protection Use in a fume cupboard and eye skin protection or use in small amounts in a well ventilated area Use in a fume cupboard and eye skin protection or use in small amounts in a well ventilated area

METHOD: 1. Place 3mL of Br water into 2 test tubes. 2. To one of the tubes add 3 drops of cyclohexane and shake the tube by flicking it briskly. 3. To the other tube, add 3 drops of cyclohexane and shake the tube by flicking it briskly. 4. Draw to diagram to illustrate observations. 5. Construct a model of cyclohexane and cyclohexene molecule, with a model kit. VARIABLES: o

Controlled variables: 1

       

Amount of Br water Amount of Cyclohexane Amount of Cyclohexene Concentration of Br water Temperature of surroundings Air Pressure Humidity of surroundings Method of mixing chemicals (Flicking 3 times)

o

Dependent variable:  The amount of Br water required

o

Independent variable:  The alkane and alkenes

IMPROVING VALIDITY:  

Repetition Using a range of different Alkanes and Alkenes

IMPROVING RELIABILITY:  

Repetition Improving measurements o Using a pipette to measure out the amount of bromine water, rather then a measuring cylinder

RESULTS:

Bromine Water

Cyclohexane w/BW

Cyclohexene w/BW

DISCUSSION: Alkenes are more reactive than alkanes due to the presence of their double bond. Alkenes go through what is called an addition reaction. It is where in an alkene; a double bond is broken and replaced with two new covalent bonds added across double bond where a foreign element/compound attaches itself. 2

E.g. Ethene + Bromine

1, 2 – dibromoethane

As mentioned above this is described as an addition reaction because extra elements are being added to the hydrocarbon and breaking the double bond. Alkanes go through a process called a substitution reaction. The substitution needs the presence of UV light to go through. An example is shown below:

E.g.

H H I I H – C – C – H + Cl2 I I H H

H Cl UV I I H – C – C – H + HCl I I H H

When for example Ethane and Bromine undergo a substitution reaction the compound HBr is formed. This is due to one of the Br being substituted with an H on the hydrocarbon. Therefore Br2 is broken into two, one atom goes and joins the hydrocarbon and the H which the Br replaces attaches on to the free Br to make HBr. CONCLUSION: Alkenes are more reactive than alkanes as seen in the results of this experiment due to the presence of their double bond.

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