DISCUSSION
In this experiment, synthesis and characterization of Alkane, Alkene and Alkyne will be examined. Aliphatic hydrocarbons are divided into three classes : alkanes are saturated hydrocarbons that contain only carbon-carbon single bonds; alkenes are unsaturated hydrocarbons that contain at least one carbon-carbon double bond; and alkynes are unsaturated hydrocarbons that contain at least one carbon-carbon triple bond. According on the result for methane is member of alkanes family there is no reaction in the dark but in bright or sunlight the bromine colour is discharged and the solution become colourless. When blow the breath across the mouth test tubes both solution turn cloudy because the present of HBr. Reaction with bromine gives an alkyl bromide. light CH4( g ) + Br 2(l )
CH3Br( g ) + HBr( g )
Alkanes can be identified using bromine dissolved in CCl 4. The dissolved bromine (Br 2) is a brown liquid and the disappearance of the brown colour indicates a reaction has taken place. Alkenes and alkynes also react with bromine in CCl 4 but their reactions are rapid while the alkane requires light and is very slow. Aromatics do not react at all with bromine under these conditions. Since the reaction is so slow, the disappearance of the brown colour may be hard to observe. This type of reaction is called a substitution reaction since the bromine is being substituted for the hydrogen. Alkenes and alkynes both have very reactive multiple carbon bonds and behave similarly in most reactions. Usually, the triple bond is changed to a double bond and the resulting compound reacts as an alkene. Alkenes can be distinguished from alkanes and aromatic hydrocarbons by their rapid reaction with bromine in CCl 4. The aromatic compounds do not react, while the alkane is very slow. The alkenes do not need light to react with bromine. This reaction provides a way wa y to test for alkenes or alkynes. Solutions of bromine in CCl4 have an intense red-orange color. When Bromine in CCl 4 is mixed with a sample of an alkane, no change is initially observed. When it is mixed with an alkene or alkyne, the colour of Bromine rapidly disappears. Evidence of a reaction is the disappearance of the brown colour of the bromine in CCl4. It should also be noted that no acidic gas is given off. This type of reaction is called an addition reaction because the bromine is being added to the chain. An additional test to
determine whether or not a compound is an unsaturated hydrocarbon is known as the Baeyer Test. Potassium permanganate (KMnO4) is purple. When added to an unsaturated hydrocarbon, the purple colour will change to a brown colour (MnO 2) that indicates a reaction has taken place. The reaction between ethene and bromine to form dibromoethane and ethyne and bromine to form tetrabromoethane are one of the addition reactions of alkenes and alkynes. Hydrogen bromide (HBr) adds across a C=C double bond to form the corresponding alkyl bromide, in which the hydrogen ends up on the carbon atom that had more hydrogen atoms to begin with. The successes of the experiment show that achieving main of the observation. The observation is success for all the hydrocarbon used moreover this experiment also determine the synthesize and characterize of saturated and unsaturated hydrocarbon. Although that in this experiment actually have an error that occur which is the wrong technique when collect the methane , ethene and ethyne (over water) . Other than that ,when weighing of aluminium oxide and anhydrous sodium carbonate the electronic weight must be in zero before start weight . By this improvement which is we must repeat the experiment three times to avoid parallex error and get accurate reading when weighing. Next, when gas was collected in test tubes must be quickly closed the test tubes with the cork to avoid excessive gas use.
CONCLUSION
The overall objectives of this experiment is to identify the synthesis and characterization of alkanes, alkenes and alkynes. The hydrocarbons were to be tested according to their reduction of any halogenated derivatives of alkanes , Bromine dissolved in carbon tetrachloride and Baeyer test . To elaborate , they were categorized and from the results were inferred whether saturated or unsaturated. Hydrocarbons may be saturated which means that each carbon is bonded to four other atoms through single covalent bonds, thus it creates the maximum number of hydrogen in a compound due to the absence of any substituent. Hydrogen atoms usually occupy all available bonding positions after the carbons have bonded to each other. While, unsaturated hydrocarbons contain either double or triple bonds. Alkenes as unsaturated compounds are also called olefins and they form oily liquids on reaction with halides like bromine gas.
APPENDIX
1. What do 'saturated' and 'unsaturated' mean when applied to hydrocarbons? Give examples of a saturated hydrocarbon and an unsaturated hydrocarbon.[5 marks]
Saturated hydrocarbon mean compound that contain only single bond such as Alkane.
While unsaturated mean compound that contains a multiple bonds such as Alkene and Alkyne.
2. Give Five (5) sources of methane. [5 marks]
Fossil Fuel Mining/Distribution : Methane is always found wherever there are fossil fuel extracted from the earth whether it is natural gas coal or oil.
Livestock : From animal and during their normal digestion process they create large amounts of methane.
Landfills : The organic matter in our garbage or open landfill gets trapped in conditions where there is no oxygen(anaerobic) and because of this large amounts of methane is created.
Biogas : Generated by the fermentation of organic matter including manure. wastewater sludge.
Carbon dioxide and hydrogen or carbon monoxide and hydrogen : Through chemical reactions.
3. Describe reactions that are characteristics of alkanes, alkenes and alkynes. [5 marks] Alkanes 1)
Alkenes
This i) Addition of Hydrogen : 1) Addition of Hydrogen:
Halogenations:
involves
Alkynes
replacement
of Addition of hydrogen to
In presence of catalyst like
hydrogen atom by halogen
alkenes takes place under finely divided Ni, Pt, or
atom.
pressure
and
in
the Pd,
alkynes
add
two
a) Chlorination: Alkanes presence of catalyst like molecule of hydrogen to
react
with
presence diffused
chlorine
U.V
light
sunlight
or
in Ni, Pt or Pd to produce or saturated at
o
give
corresponding
hydrocarbons. alkanes. The reaction can
This is called catalytic be stopped at alkene stage
temperature 300-400 C to
hydrogenation.
by
form
ii) Addition of Halogen:
Catalyst (Pd deactivated
the
corresponding
Alkenes reacts to halogen
using
Lindlar’s
substituted products.
in presence of inert solvent by BaSO + quinoline)
For
to
example
4
:Methane
give
dihalogen
2) Addition of Halogen:
reacts with chlorine to give
derivative for example.
mixture
iii)Addition of Hydrogen form first dihalide and Halide-(Hydro then tetra halide.
of
different
substituted products.
Halogens add to alkyne to
It is difficult to stop this
halogenation) : Addition 3) Addition of Halogen reaction at first step. of Hydrogen halide to Acids: Two molecule of However, the yield of alkene produce alkyl halogen acids can be
CH Cl can be improved by 3
taking excess of methane. Ethane and higher alkanes
halides.
In
case
of added to symmetrical symmetrical alkene only alkynes in two stages. one alkyl halide is formed After addition of one
react with chlorine in a but when the olefin is molecule alkyne become two unsymmetrical derivative similar way and all possible unsymmetrical substitution products are products are possible. of alkene so that the obtained.
addition
2)Aromatisation:
molecule
of
a
takes
Conversion
of
aliphatic
according
compound
to
aromatic
Markonikov’s rule
second place to . Thus
compounds is known as
both the halogens become
aromatisation.
attached
containing
Alkanes
6-10
carbon
to
the
same
carbon atom.
atoms are converted into
In case of unsymmetrical
benzene
alkynes
homologous temperature
and
its
at
high
and
in
the
presence of catalyst. 3)Sulphonation:This
involves
replacement
hydrogen atom by
of
– SO
3
H
group. It is carried out by heating
alkanes
with
fuming sulphuric acid or at higher temperature.
addition
takes
place in accordance with Markonikov’s rule.
4. Write a balanced equation for the reaction which methane was obtained by the reduction of chloroform.[5 marks]
RX
reduction
HX
Chloroform (CHCl 3) is made by taking methane adding chlorine and then heating the compound up until between 400 and 500 degrees Celsius. Methane (CH 4) can be obtained from manure from animals when the manure ferments over time. Chlorine gas (Cl 2) was invented in week 4. The chemical formula for this is :
CH4 + Cl2 CH3Cl + HCl
After this, you take the CH 3Cl, or chloromethane, and repeat the process with the chloromethane instead of the methane. This causes the products to contain progressively more chlorine: CH3Cl + Cl2 CH2Cl2 + HCl
Then repeat the process again using dichloromethane, and then chloroform respectivel y:
CH2Cl2 + Cl2 CHCl3 + HCl CHCl3 + Cl2 CH4 + HCl
The products formed are: chloromethane, dichloromethane, chloroform, and carbon tetrachloride. They are then separated by distillation.
5. Provide 2 (TWO) other methods of collecting gas that can be used in this experiment.[5 marks]
Cracking hydrocarbon. In this experiment the vapour of liquid paraffin (a mixture of saturated hydrocarbons ) is cracked by passing it over a heated catalyst. The mixture of gaseous short-chain hydrocarbons produced is collected and tested for unsaturation with bromine water and acidified potassium manganate(VII ) solution.
Thermal cracking (by heat).
