UNIVERSITI PENDIDIKAN SULTAN IDRIS

SKO 3013

BASIC ORGANIC CHEMISTRY

LABORATORY REPORT 3

EXPERIMENTS FOR HYDROCARBONS

NAME MATRIC NUMBER

SITI NOR AMIRA BT MOHMAD

NOOR

D20091035073

NORHIDAYAH BINTI MOHD

AMIN

D20091035082

PENDIDIKAN SAINS

SEMESTER 1 (2011/2012)

LECTURER:

DR SARIPAH SALBIAH BT SYED ABDUL AZZIZ.

Experiment 3: Hydrocarbon

Objective:

Upon completion of this experiment, students should have learned :

1. Some reactions of hydrocarbon

2. Chemical and physical properties of hydrocarbon

3. Comparison of different classes in hydrocarbon

Introduction:

Qualitative organic analysis is for identification and characterization of unknown organic

compounds. It is an important part of studying the organic chemistry. Every chemist must

learn the appropriate methods for establishing to identify the organic compound. In this

experiment, you will be issued with unknown compounds and will be asked to identify it

through chemical methods.

With general unknown, you must first determine the class of compound to which the

unknown belongs, that is identify its main functional group, then you must determine the

specific compound in that corresponds to the unknown.

Procedure:

1. Alkane reactions

A. Ignition test

Small amount of heptane placed on spatula. Placed it in the flame of a Bunsen burner

Sooty flame result observed

B. Bromine test

Small amount of 0.5% bromine in CCl4 placed in 2 test tube (A and B)

5-10 drops of heptane added in both test tubes and shaked well

Test tube A, in dark room (cabinet)

Test tube B, expose to sunlight

Observed (after 30 minutes)

C. Bayer test

Aqueous solution of KMnO4 slowly added drop by drop while shaking into 2ml

heptane

Colour changing observed within 1minute

D. Sulphuric acid test

3-4 drops of heptanes added slowly into 2ml H2SO4 in a test tube

Colour change recorded

2. Alkenes Reactions

Step A, B, C and D was repeated by replaced heptanes with cyclohexene

3. Alkynes Reactions

A. Bromine test

Acetylene gas trapped in tube and close with rubber stopper

5 drops bromine solution added in the tube (contain acetylene gas)

Shake it well

Observation recorded after 30 minutes

B. Baeyer test

Acetylene gas trapped in a test tube

5 drops of KMnO4 (aqueous solution) added in test tube, and shakes well

Colour changes (reagent) observed within 1minute

Result:

ReagentTest

Difference between alkanes , alkenes and alkynes.Heptane cyclohexene Acetylene

Ignition Reaction

Less sooty Yellow flame Less dark of

sooty.

More sooty Yellow flame Dark of sooty.

-

Bromine test(sunglight)

No colour change

Decolourise the Bromine water

(colourless)

Decolourise the Bromine water

(colourless)

Bromine test(dark room)

No colour change

Decolourise the Bromine water

(colourless)-

Bayer test No colour

change. Purple to

brown colour

Colourless Precipitated

Sulphuric Acid test

Decolourise (colourless)

Brown colour -

Discussion:

Hydrocarbons are the simplest organic compound it containing only carbon and hydrogen. It

can found in straight chain, branced chain, or cyclic molecules. Carbon tend to form four

bond in a tetrahedral geometry. Alkanes, alkenes and alkynes are hydrocarbons.In this

experiment we used heptane, cyclohexene and acetylene to represent alkanes, alkenes and

alkynes.

We conduct the experiment for alkanes, alkenes and alkynes to identify the chemical and

physical properties of hydrocarbon. And we also can determine the comparison of different

classes in hydrocarbon. We know the general formula to identify alkane is CHnH2n+2, for

alkenes is CHnH2n and for alkynes CHnH2n-2. Beside that, the physical state for alkanes are its

members having 1-4 carbon atoms per molecule are gases 5-17 carbon atoms are liquids and

18 or more are solids at room temperature, then for alkenes its members having 2-4 carbon

atoms per molecule are gases 5-15 carbon atoms per molecule are liquids and the higher

members are solids and last for alkynes its members having 2-4 carbon atoms per molecule

are gases5-13 are liquids and the higher members are solids. After that, alkanes, alkenes and

alkynes has their melting and boiling point. the melting and boiling point will increase as

increase in molecular mass. so alkynes has higher melting and boiling point because their

molecular mass is higher.

From ignition test, we are observe the sooty flame result for heptane and cyclohexene.

Heptane produce less sooty yellow flame and less dark of sooty while cyclohexene produce

more sooty yellow flame and dark of sooty. It’s occurs because the percentage of carbon in

cyclohexene is higher than heptane. Then them producing CO2, H2O and heat.

After that, we conduct the bromine test to heptane, cyclohexene and acetylene. In heptane the

color of bromine water is is not change in two condition either in sunglight or dark room . It

is because heptane not undergo the reaction as they are saturated. For cyclohexene the colour

of bromine water is decolourise. It is because cyclohexene undergo the reaction with light.

Besides, it also undergo in dark room. At below the reaction of cyclohexene is occurs in dark

room :-

when used as bromine water, the corresponding bromohydrin is formed instead. On

approaching the electron dense area of the p bond of cyclohexene, the bromine molecule

becomes polarized. The electron density of the bromine is shifted, so that one bromine is

partially positive and the other is partially negative charged. The Br-Br bond is heterolytically

cleaved. The positively charged bromine atom acts as an electrophile, reacting with the C=C

double bond. A cyclic bromonium ion is formed. The subsequent attack of the bromide ion on

the three-membered ring can proceed only from the back-side, because the front-side attack is

sterically hindered. For acetylene it also decolorise the colour of Bromine water. Its reaction

same as cyclohexene.

H-C≡C-H + Br2 H(Br)C=C(Br)H (colourless)

For bayer test, heptane not undergo the reaction and the result is no colour change.while in

cylohexene permanganate convert cyclohene into diol and it course of the reaction purple

manganate is reduced to brown. Then the precipitate occurs. That precipitate is manganese

dioxide.

For acetylene the colour change to colourless and contain the precipitate it occurs when

acetylene react with kMnO4 it will produce acetylene into diol and decolourise the purple

colour of kMnO4.

For the suphuric acid test heptane decolorise while cyclohexene turn to brown colour this is

because the electrophilic addition reaction between cyclohexe and sulphuric acid. the pi bond

breaks and the pair of electrons is used to form a bond with the hydrogen atom. Then the

electrons in the hydrogen-oxygen bond are pushed on to the oxygen atom giving it a full

negative charge. After that, the lower carbon atom in the original C=C bond becomes

positively charged because the electron it originally supplied to the pi bond has been moved

away to form the new bond.

Conclusion:

From ignition test the alkenes group produce more sooty and yellow flame.

In Bromine test alkanes not undergoes any reaction but alkenes and alkynes undergoes

reaction and the bromine water decolourise.

In Bayer test,alkane not undergo the reaction the result is no colour change in alkenes

it turn to brown and for alkynes it will colourless because the reaction fully react and

precipitate is form.. The precipitate is manganese dioxide.

Sulphuric acid decolourise in heptane and brown colour in cyclohexane.

References:

Diperolehi oktober 29, 2011 daripada http://hyperphysics.phy-astr.gsu.edu/hbase/organic/

hydrocarbon.html

Diperolehi oktober 29, 2011 daripada http://www.scribd.com/doc/52376425/4-Comparing-alkanes-and-alkenes-AE

Brown colour

Diperolehi oktober 29, 2011 daripada http://www.tutorvista.com/content/chemistry/chemistry-i/coal-petroleum/alkyne-alkene-alkane.php

Laboratory Manual SKO 3013 Basic Organic Chemistry.