OBJECTIVE 1. To study the chemical properties of an alkane and an alkene. 2. To differentiate an alkane from an alkene.
INTRODUCTION Organic compound are compounds which we mostly use in our daily life activities and except for few inorganic salts and ever-present water, everything we put or on body being food, medicine, cosmetics and clothing consist of organic compounds. Some of these organic compounds in their raw states are useless and toxic unless they converted into suitable forms and some of these are carried out by cracking that is in petroleum, and also synthesis as in polymerisation. Hence it is the duty of chemical engineers to know the characteristics, classes and type of reaction under which these compounds undergo in order to convert them into useful products. Organic compounds are compounds which contain carbon, hydrogen, oxygen, nitrogen, sulphur and halogens. Organic compounds are divided into classes and each of them are characterised by a functional group. A functional group is a chemically bond atoms that shows characteristics set of properties. Hydrocarbons are an organic compound that contains carbon and hydrogen and they are classified according to their structure. Primarily hydrocarbons are divided into aliphatic and aromatic hydrocarbons. Aliphatic compounds are carbon compounds arranged in open chains and can be straight chained, branched and can contain single, double or triple bonds. Aliphatic compounds are divided into three classes; those with single bonds are called alkanes and are said to be saturated and those with double or triple bonds are alkenes and alkynes and are unsaturated compounds. Aromatic compounds on the other hand are compounds containing close rings of carbon atoms in which the pi-electron are delocalised across the structure. They are referred to as benzene ring compounds and may also contain other atoms like oxygen and nitrogen. In this experiment the various hydrocarbons are analysed based upon their fundamental reactions when they are subjected to various varieties of reagents under some experimental conditions which would be used to distinguish them.
APPARATUS White tile Dropper Test tube Water bath Rubber band Wood splint Labelling paper Evaporating dish Black sugar paper (6 x 12cm)
CHEMICAL REAGENTS Dichloromethane Cyclohexane Cyclohexene Acidified KMnO4, 0.01 M 4% bromine in dichloromethane
PROCEDURE (A)Combustion test 1. 1 ml of cyclohexane and cyclohexene has been placed in two separate evaporating dishes. 2. Both compound has been ignited simultaneously with a burning wood splint. 3. The colour intensity of the flame and soot given off has been compared. 4. The observation has been recorded.
(B)Reaction with bromine in dichloromethane 1. 4 dry of clean test tube has been labelled with A to D. 2. 1 ml of cyclohexane has been placed in test tubes A and B and 1 ml of cyclohexene has been placed in test tubes C and D. 3. Test tube A and C has been wrapped with black sugar papers. 4. 4 to 5 drops of 4% bromine in dichloromethane has been added into each test tube. 5. Test tube A and C has been kept in a dark place, and test tube B and D in the sunlight. We leaved them for 10 minutes. 6. The observations has been recorded.
(C)Oxidation with acidified KMnO4 1. 2 dry of clean test tubes has been labelled with G and H. 2. 1 ml each of cyclohexane and cyclohexene has been placed in test tubes G and H respectively. 3. 5 drops of acidified KMnO4 has been added into each test tube. 4. The test tube was heated in a water bath at 70 to 80oC for 10 – 15 minutes. 5. The observations has been recorded.
RESULT (A)Combustion test Compound Alkane
Observation Produce less soot
(cyclohexane) Alkene
Produce less colour intensity Produce more soot
(cyclohexene)
Produce more colour intensity
(B)Reaction with bromine in dichloromethane Compound A B C D
Observation No colour changing Change to colourless Change to colourless Change to colourless
(C)Oxidation with acidified KMnO4 Compound G H
Observation Change to purple solution Change to brown solution
DICUSSION Although all hydrocarbons contain carbon and hydrogen, they have different properties. The most common property used to distinguish these hydrocarbons is based on their reaction with
other compounds. From the first experiment, Cyclohexane is a saturated hydrocarbon and cyclohexene is an unsaturated hydrocarbon due to the presence of double bond. Both hydrocarbons produce carbon dioxide and water during combustion test. When the oxygen is limited, the product will be carbon monoxide and water. Cyclohexene burns and produces more soot because of the higher percentage of carbon compared to cyclohexane. In the second experiment, when bromine water was added to cyclohexane and shaken and was also kept in the dark, no colour change was observed which indicated presence of an alkane. But when this same mixture was exposed to the sunlight there was an observable colour change and evolution of hydrogen bromide gas. These observable characteristics are very specific of alkanes which undergo substitution reaction under sunlight. Also when bromine water was added to cyclohexene, the bromine water decolourised rapidly under room temperature with evolution of hydrogen bromide gas which indicated the presence of an alkene as they undergo addition reaction under these conditions. In the third experiment when drops of KMnO4 solution was added to cyclohexane and shaken there was no observable reaction which indicated the presence of an alkane as alkanes are unreactive towards oxidizing agents. However when the same drops of KMnO4 solution was added to cyclohexene, there was a decolourisation of the KMnO4 solution colour which is characteristics of alkenes as they readily oxidised at room temperature.
CONCLUSION Our objectives is achieved. In this experiment, the properties and the difference between an alkane and alkene is identified. Hence, this experiment is a success. Alkane is identified from alkene by its properties. It can be seen from the tests conducted in the experiment that alkene is much more reactive than alkane. This is due to its carbon-carbon double bond since it is an unsaturated hydrocarbon. Alkenes undergo a lot of addition reaction while alkane does not undergo any addition reaction in the experiments conducted. Instead, alkane only undergo halogenation which is a substitution reaction when react with bromine water. Thus, alkene is more reactive than alkane.
REFERENCES 1. Laboratory manual book chemistry semester 2 UniKL NAFAS CPS. 2. https://www.scribd.com/doc/29340429/Reaction-of-Hydrocarbons
