Download Hydrocarbons Activity - Valley Catholic School

Name: ______________________________
Date: ______________
Honors Chemistry
Period: _________
Hydrocarbons Activity
Hydrocarbons are important fuels. They are often called “fossil fuels” because of their
source. They react with oxygen to form carbon dioxide, water, and energy.
1. Write the general equation for a combustion reaction, assume “fossil fuel” is used:
2. The simplest hydrocarbons are the alkanes. Alkanes are called saturated
hydrocarbons, because all the bonds between the atoms of alkanes are single covalent
bonds. The formulas and names of the 5 smallest alkanes are given below. Use the
model kits to build models of these molecules, and record the structures.
a) methane, CH4
b) ethane, C2H6
c) propane, C3H8
d) butane, C4H10
e) pentane, C5H12
3. All of the alkanes have the general formula, CxH2x+2.
a) Use this general formula to predict the formulas of some larger alkanes.
Name
Number of carbons Number of hydrogens
Formula
Hexane
6
Tridecane
13
?
100
Octane
b) Can you offer an explanation for the fact that there are 2x+2 hydrogens for every x
carbons in an alkane? (Look at the structures for the pattern.)
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Rev 09 Dec 2008
Name: ______________________________
Date: ______________
Honors Chemistry
Period: _________
c) What is the hybridization for each of these molecules?
4. Notice the similarities in the names of the different alkanes. Describe how alkanes are
named. In your description, make up a formula of an alkane not in this activity and give
your alkane a name that fits the pattern. (See Chap 22)
5. Isomers are molecules with the same molecular formulas, but different structural
formulas. The different arrangements of the atoms of isomers give the compounds
slightly different properties. Alkanes can be straight chain or branched. Straight-chain
means the carbons are all linked one after another. Branched refers to the branching of
carbons off a longer chain. Branched alkanes are more valued in gasoline, and give
gasoline a higher octane rating. Use the model kits to help you find the structure of the
branched isomer of butane.
a) Give its structural formula:
b) Now use the model kits to find 2 branched isomers of pentane. Draw the structural
formulas.
6. Alkenes are a type of unsaturated hydrocarbon, because they have less than the
maximum number of hydrogen atoms. They are characterized by one carbon to carbon
double bond. The general formula for an alkene is CxH2x. Use the model kits to
determine the structure of the following alkenes and record the structural formulas.
a) ethene, C2H4,
b) propene, C3H6,
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Rev 09 Dec 2008
Name: ______________________________
Date: ______________
Honors Chemistry
Period: _________
c) butene, C4H8,
d) draw another isomer of butene
e) predict the name and formula of the alkene with 100 carbons
f) What is the hybridization for each of these molecules?
3
Rev 09 Dec 2008
Name: ______________________________
Date: ______________
Honors Chemistry
Period: _________
Bonus Challenge: Below is a table of the first 20 straight-chain alkanes and their
properties. Complete the table, and then use it to answer the following questions:
a) Which alkanes are gases at 25oC?
b) Which alkanes are liquid at 25oC?
c) Which alkanes are solid at 25oC?
d) What is the relationship between the molar mass of alkanes and their melting and
boiling points? (Write a complete sentence.)
e) Explain the boiling point trend in terms of energy.
Some Properties of the Alkanes
Name
Methane
Ethane
Propane
n-Butane
n-Pentane
n-Hexane
n-Heptane
n-Octane
n-Nonane
n-Decane
n-Undecane
n-Dodecane
n-Tridecane
n-Tetradecane
n-Pentadecane
n-Hexadecane
n-Heptadecane
n-Octadecane
n-Nonadecane
n-Eicosane
Formula
CH4
C2H6
C3H8
C4H10
C5H12
C6H14
C7H16
C8H18
C9H20
C10H22
M.P. (oC)
Molar mass
(g/mol)
16
30
44
58
72
86
100
114
128
142
-183
-172
-187
-138
-130
-95
-90.5
-57
-54
-30
-26
-10
-6
5.5
10
18
22
28
32
36
B.P. (oC)
-162
-88.5
-42
0
36
69
98
126
151
174
196
216
235.4
253.7
270.63
287
301.8
316.1
329.7
343
Density @ 20oC
(g/mL)
0.001432
0.0012291
0.0018024
0.0023758
0.626
0.659
0.684
0.703
0.718
0.730
0.740
0.749
0.7564
0.7628
0.769
0.773
0.7780
0.7768
0.7855
0.7886
For further study (extra credit), you may research other classes or types of
hydrocarbons and report on their characteristics, such as identifying features, structural
formulas, and naming. You might also include their industrial or biological importance.
Other classes of hydrocarbons might include the alkynes, alcohols, carboxylic acids, etc.
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Rev 09 Dec 2008