Hydrocarbons Lab
Hydrocarbons are compounds made primarily of carbon and
hydrogen. An alkane is a hydrocarbon containing only single bonds.
An alkene contains one or more carbon-carbon double bonds.
Alkynes have one or more carbon-carbon triple bonds. Aromatic
hydrocarbons contain a circular pattern of double and single bonds
where the double bonded electrons can travel completely around the
ring.
Saturated hydrocarbons contain no double bond or triple bonds.
Alkanes are saturated. Unsaturated hydrocarbons contain double or
triple bonds. Alkenes, Alkynes, and Aromatic hydrocarbons are all
unsaturated.
Examples:
Alkane
Alkene
Alkyne
Aromatic
(saturated)
(unsaturated)
(unsaturated)
(unsaturated)
Propane
Propene
Propyne
Benzene
H
H
H H H
H C C C H
H
H
H
C C
H H H
C H
H H
H
H C C C H
H
H
C
C
C
C
C
C
H
H
H
Alcohols are hydrocarbons that contain an –OH bonded to a regular
carbon. Phenols are aromatics that contain the alcohol group.
Alcohol
Phenol
H
H
H
H C O H
H
Methanol
(Methyl alcohol)
H
C
C
C
C
H
C
C
O H
H
Phenol
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Physical Properties:
Volatility: Because of the small difference in electronegativities
between carbon (C=2.5) and hydrogen (H=2.1), hydrocarbons are
characteristically nonpolar. Since hydrocarbons do not have partially
negative or partially positive atoms there is minimal attraction between
hydrocarbon molecules. Thus, hydrocarbons require less energy to
evaporate or vaporize than do polar compounds. Small hydrocarbons
require less energy to vaporize than large ones. They are highly volatile.
Odor: The volatile nature of hydrocarbons causes them to vaporize and
move through the air. These air-borne molecules reach our noses and we
smell them. Many hydrocarbons have characteristic odors.
Solubility: The nonpolar character of hydrocarbons allows them to
have minimal attraction to other hydrocarbons but causes them to repel
polar compounds such as water.
Density: Nonpolar hydrocarbons have minimal attraction to each other
so hold together loosely. They have low density. Polar compounds, on the
other hand, attract each other and bind close. Water has a lot of
hydrogen bonding and is particularly dense.)
Chemical Properties:
Combustion: Hydrocarbons easily combust in the presence of oxygen.
They are commonly used for fuel. Wood, fuel oil, gasoline, diesel, and
candle wax are all common flammable hydrocarbons fuels.
CH4
methane
+
2O2
CO2
oxygen
carbon dioxide
+
2H2O
water
Not all hydrocarbons will react with the same amount of oxygen so when
burning in a normal atmosphere they may appear very different.
Aromatic hydrocarbons, for example, burn very dirty in that they
undergo incomplete combustion and produce a lot of soot. Small
hydrocarbons and alcohols are more likely to completely combust and
burn cleanly, with very little or no soot.
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Bromination: The double bond of an alkene reacts with halogens to
form alkyl halide compounds. The pi bond (second bond) of the double
bond is weak and breaks more easily than the sigma bond (first bond).
H
H
C C
H
Br2
+
CH3
propene (colorless)
bromine (brown)
Br Br
H C C H
CH3
H
1,2-dibromopropane (colorless)
Bromine (Br2) is a brown liquid so if a reaction occurs in which the Br2
splits apart and the Br’s bond with carbons we will see the brown color
disappear.
Aromatic compounds do not react with halogens in the same way. The
double bonds of an aromatic compound are stronger and so do not easily
break.
Oxidation: Some hydrocarbons are easily oxidized with potassium
permanganate, KMnO4.
H
H
+
C C
H
KMnO4
CH3
potassium permanganate (purple)
propene (colorless)
HO OH
H C C H
CH3
H
+
MnO2
manganese (IV) oxide (brown)
1,2-propandiol (colorless)
Potassium Permanganate is purple so if a reaction occurs in which the
KMnO4 oxidizes the carbons we will see the purple KMnO4 change to
brown MnO2.
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Procedures:
I. PHYSICAL PROPERTIES:
A. Volatility:
1. Obtain three small beakers of identical size. Label them #1, #2, #3.
2. Into beaker #1 put 5 mL of water.
Into beaker #2 put 5 mL of ethanol.
Into beaker #3 put 5 mL of hexane.
3. Carefully weigh each beaker on the electronic balance and record the
masses on your report sheet.
4. Weigh each beaker again every 15 minutes and record the masses.
5. On the report sheet make a graph of the total mass lost by each
substance every 15 minutes. Draw a straight line through the graph
points to show the linear relationship for the evaporation of each
liquid. Compare to determine relative volatility.
B. Solubility in Water:
1. Obtain 4 stoppered test tubes, each containing 2 mLs of water.
2. Into tube #1 put 1 mL ethanol. (C2H5OH)
Into tube #2 put 1 mL of hexane. (C6H14)
Into tube #3 put 1 mL cyclohexene. (C6H10)
Into tube #4 put 1 mL toluene. (C6H5CH3)
Stopper the tubes and shake each to mix.
3. Check each tube for layers. Record your observations about the
solubility of each hydrocarbon in water. Use ‘S’ for soluble, ‘PS’ for
partially soluble, and ‘I’ for insoluble. Save these tubes for use in
Part IC.
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C. Density:
4. For each insoluble hydrocarbon in Part IB observe the positioning of
the hydrocarbon layer relative to water. The more dense substance
will be on the bottom.
5. Record the density of each hydrocarbon relative to water on the report
sheet. Report M for more dense than water, L for less dense than
water, and X if there is not enough evidence to determine.
6. Dispose of hydrocarbons in the designated waste containers.
D. Solubility in Other Hydrocarbons:
1. Obtain 3 dry stoppered test tubes, each containing 1 mL of hexane
(C6H14).
2. Into tube #1 put 1 mL ethanol. (C2H5OH)
Into tube #2 put 1 mL cyclohexene. (C6H10)
Into tube #3 put 1 mL toluene. (C6H5CH3)
Stopper the tubes and shake each to mix.
3. Check each tube for layers. Record your observations about the
solubility of each hydrocarbon in hexane (a typical hydrocarbon
solvent).
Dispose of hydrocarbons in the designated waste containers.
II. CHEMICAL PROPERTIES:
A. Combustion:
1. Line up 4 clean and dry watch glasses about 6 inches apart in a
fume hood.
2. Onto
Onto
Onto
Onto
watch
watch
watch
watch
glass
glass
glass
glass
#1
#2
#3
#4
put
put
put
put
10
10
10
10
drops
drops
drops
drops
ethanol. (C2H5OH)
of hexane. (C6H14)
cyclohexene. (C6H10)
toluene. (C6H5CH3)
3. Quickly go down the row and ignite each liquid with a burning wood
splint and compare the colors and types of flames produced by each
hydrocarbon as they burn together.
Record your observations.
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B. Bromination:
1. Obtain 4 dry stoppered test tubes.
2. Into
Into
Into
Into
tube
tube
tube
tube
#1
#2
#3
#4
put
put
put
put
1
1
1
1
mL
mL
mL
mL
ethanol. (C2H5OH)
hexane. (C6H14)
cyclohexene. (C6H10)
toluene. (C6H5CH3)
3. Move your tubes to a fume hood and into each tube drop 3 drops of
Bromine (Br2) solution. Swirl to mix if needed and record any
results.
4. Dispose in the designated waste containers. Tubes containing
bromine must go into “bromine waste”.
C. Oxidation:
1. Obtain 4 clean stoppered test tubes.
2. Into
Into
Into
Into
tube
tube
tube
tube
#1
#2
#3
#4
put
put
put
put
1
1
1
1
mL
mL
mL
mL
ethanol. (C2H5OH)
hexane. (C6H14)
cyclohexene. (C6H10)
toluene. (C6H5CH3)
3. Into each tube drop 3 drops of Potassium Permanganate (KMnO4)
solution. Stopper and shake to mix well. Record any results.
Dispose in the designated waste containers.
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Name
Date
Report for Experiment: Hydrocarbons
I. PHYSICAL PROPERTIES:
A. Volatility:
a. Mass at Start
b. Mass lost in zero min
c. Mass at 15 minutes
d. Total g’s lost from beginning
e. Mass at 30 minutes
f. Total g’s lost from beginning
g. Mass at 45 minutes
h. Total g’s lost from beginning
i. Mass at 60 minutes
j. Total g’s lost from beginning
#1 + Water
#2 + Ethanol
#3 + Hexane
Mass in grams
Mass in grams
Mass in grams
Og
Og
Og
(a-c)
(a-c)
(a-c)
(a-e)
(a-e)
(a-e)
(a-g)
(a-g)
(a-g)
(a-i)
(a-i)
(a-i)
Mass lost by Water (#1), Ethanol (#2), and Hexane (3#)
Total
Mass
Lost
From the
Beginning
(in grams)
0
15
(a-c)
30
45
(a-e)
Time
(a-g)
60
(a-i)
(in minutes)
Volatility Results Summary: Rank the substances in order of decreasing volatility.
Most volatile
>
>
Least volatile
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Ethanol
Hexane
Cyclohexene
Toluene
An Alcohol
An Alkane
An Alkene
An Aromatic
B. Solubility
in Water
C. Density
Compared to Water
D. Solubility
in Hydrocarbons
Physical Properties Results Summary:
1.
As
A.
B.
C.
a general rule, most hydrocarbons are _____ than water.
more volatile
less volatile
there is no general rule
2.
As a general rule, hydrocarbons are _____ in water and _____in
other hydrocarbons.
A. soluble, soluble
B. insoluble, soluble
C. insoluble, insoluble
D. soluble, insoluble
3.
As
A.
B.
C.
a general rule, most hydrocarbons are _____ than water.
more dense
less dense
there is no general rule
II. CHEMICAL REACTIVITY:
A. Combustion
B. Bromination
(reaction w/ Br2)
C. Oxidation
(reaction w/ KMnO4)
Ethanol
Hexane
Cyclohexene
Toluene
An Alcohol
An Alkane
An Alkene
An Aromatic