Hydrocarbon Lab Activity 1

Purpose: To examine the shape and character of the bonds in hydrocarbons

Pre-lab:

  1. Draw the structural formula for the following hydrocarbons
  2. butaneb. 1-butenec. 1,3-butadiened. 2-butyne
  3. Have your teacher initial your diagrams before you begin

Procedure:

  1. Build a model for each of the 4 hydrocarbons from your pre-lab
  2. Identify the different types of bonds in each hydrocarbon
  3. Try to rotate each hydrocarbon. Which bonds allow rotation around the bond? Which bonds prevent rotation?
  4. Examine the shape of the molecule around each carbon atom. Draw diagrams to show your observations.

Analysis:

  1. Describe the shape around a C atom with:
  2. Only single bonds
  3. One double and two single bonds
  4. One triple and one single bond
  5. Two double bonds
  6. Try to construct and name a different model for butane. What is the name for a molecule where more than one structure is possible?
  7. Molecular model kits are a good representation of real atomic geometry. Are you able to make a quadruple bond between two carbons with the model kit? What does this tell you about real carbon bonding?

Alkane Boiling Points Lab Activity 2

Chemists often gather data regarding physical and chemical properties of substances. Although this data can be organized in many ways, the most useful ways uncover trends or patterns.

Here is data for boiling points of straight chain alkanes. During evaporation and boiling, individual molecules in the liquid state gain enough energy to overcome intermolecular forces and enter the gaseous state.

Table 1: Alkane boiling points

Alkane / Boiling Point (˚C)
Butane / -0.5
Decane / 174.0
Ethane / -88.6
Heptane / 98.4
Hexane / 68.7
Methane / -161.7
Nonane / 150.8
Octane / 125.7
Pentane / 36.1
Propane / -42.1

Analysis:

  1. In what pattern is the data in Table 1 organized? Is this a useful way to present the information? Explain.
  2. Propose a more useful way to arrange this data. Plot a graph based on your idea.
  3. Use your graph to determine
  4. Which substance(s) are gases at SATP.
  5. Which substance(s) boil between SATP and body temperature.
  6. What can you infer about intermolecular forces in decane compared to butane?
  7. Intermolecular forces also help explain other liquid properties such as freezing point and viscosity. Based on their intermolecular forces, rank pentane, octane and decane in order of increasing viscosity (i.e. 1 = least viscous, “flows most readily”)

Alkane Isomer Boiling Points Lab Activity 3

You have already observed that the boiling points of straight chain alkanes are related to the number of carbon atoms in their molecule due to the increased number of intermolecular forces.

Consider the boiling points for the isomers below.

Table 2: Isomer Boiling Points

Structural Formula / Boiling Point (˚C)
C5H12 Isomers / CH3-CH2-CH2-CH2-CH3 / 36.1
CH3-CH-CH2-CH3
I
CH3 / 27.8
CH3
I
CH3-C -CH3
I
CH3 / 9.5
C8H18 Isomers / CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH3 / 125.6
CH3-CH2-CH2-CH2-CH2-CH-CH3
I
CH3 / 117.7
CH3
I
CH3-CH-CH2-C-CH3
I I
CH3 CH3 / 99.2
  1. How does the boiling point change as the number of carbon side chains increases?
  2. Match each boiling point to the appropriate C7H16 isomer: 98.4˚C, 92.0˚C, 79.2˚C

a) CH3-CH2-CH-CH2-CH2-CH3
I
CH3 / c) CH3
I
CH3-C-CH2-CH2-CH3
I
CH3
b) CH3-CH2-CH2-CH2-CH2-CH2-CH3
  1. Compare the following C8H18 isomer to the isomers in Table 2. Predict its approximate boiling point.

CH3

I

CH3-CH2-C-CH2-CH2-CH3

I

CH3

Extra practice: Name all the isomers that were examined in this activity.