ChemCom Unit 3: Boiling Point Trends of Alkanes

Name _____________________________ Period _______
ChemCom Unit 3: Boiling Point Trends of Alkanes
Chemists often gather and analyze data about the physical and chemical properties of
substances. These data can be organized in many ways, but the most useful techniques are
those that uncover trends or patterns among the data. Use the data in the table below to
answer the questions that follow.
Boiling Points of the First Ten Alkanes
Alkane Molecular Formula Boiling Point (ºC)
Butane C4H10 -0.5
Decane C10H22 174.0
Ethane C2H6 -88.6
Heptane C7H16 98.4
Hexane C6H14 68.7
Methane CH4 -161.7
Nonane C9H20 150.8
Octane C8H18 125.7
Pentane C5H12 36.1
Propane C3H8 -42.1
1. In what pattern or order are the data in the table organized?
2. Suppose you were searching for a trend or pattern among these boiling points. Propose a
more useful way to present the data and reorganize the table in the space below:
Alkane Molecular Formula Boiling Point (ºC)
3. Which alkanes are gases at room temperature (22ºC)?
4. Which alkanes have a higher normal boiling point than water (100ºC)?

5. On a sheet of graph paper, prepare a graph of boiling point (y-axis) vs. number of carbons
(x-axis). The x-axis should range from 1 to 13 carbons and the y-axis should extend from
-200ºC to +250ºC. Choose an appropriate scale so that the whole sheet of graph paper is
used. Label your axes and give the graph a descriptive title.
6. Draw a best-fit line through your points. From the graph, estimate the average change in
boiling point (in ºC) when one carbon atom and two hydrogen atoms (CH2) are added to
an alkane chain.
Average change in Boiling Point = _____________ ºC
7. Using your graph, estimate the boiling points of undecane (C11H24), dodecane (C12H26),
and tridecane (C13H28). To do this, continue the trend of your graph by drawing a dashed
line from the best fit line you drew for the first 10 alkanes. This is called extrapolation.
Then, read your predicted boiling points on the y-axis:
C11H24 = _____________ C12H26 =_____________ C13H28 =_____________
8. The actual boiling points for undecane, dodecane, and tridecane are listed below. How
do your predicted boiling points compare?
Alkane Molecular Formula Boiling Point (ºC)
Undecane C11H24 196
Dodecane C12H26 216
Tridecane C13H28 235
9. Intermolecular Forces are the attractive forces between molecules. Out of the 13
alkanes discussed in this assignment, which has the strongest intermolecular forces?
Explain your answer carefully.
Don’t forget to attach your graph!