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Science · Drill 24

Science practice 24

8 questions ~9 min recommended
⏱ 00:00
Score
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Alcohols
Alkanes
Name
Pentane
Hexane
Heptane
Butanol
Pentanol
Hexanol
Molar Mass (g/mol)
72
86
100
74
88
102
Skeletal Model
. OH

Boiling Points (*C) vs. Molar Mass for Organic Compounds
150 -
•
1100 -
•
50 -
•
• Alkanes
• Alcohols
0+
70
80
90
Molar mass (q/mol)
100
110

The boiling point of a liquid is commonly defined as the temperature at which the vapor pressure of the liquid is equal to the atmospheric pressure that surrounds the liquid. When a liquid is brought to a temperature at or above its boiling point, it quickly changes from the liquid phase to the gaseous phase. This can easily be observed in vapor bubbles that form in the liquid and rise to the top.

The boiling point of a substance depends on many different factors, such as the composition of the substance, its molar mass, and the atmospheric pressure surrounding it. The names, molar masses, and skeletal models of a variety of alkanes and three alcohols were identified and recorded in Table 7.2.

TABLE 7.2

Figure 7.4 shows the boiling points of these six substances versus their molar mass. All temperatures are in degrees Celsius and have been recorded at a standard atmospheric pressure of 1 atm.

Figure 7.4

1. What is the boiling point of heptane?

2. Based on Figure 7.4, what is the best summary of the relationship between the molar mass and boiling point of an alkane?

3. The organic substance propanol has a molar mass of about 60 g/mol. Which temperature is most likely the boiling point of propanol?

4. In which physical state would pentanol be if the atmospheric pressure were 1.0 atm and the temperature were 150°C?

5. Based on the skeletal models shown in Table 7.2, which statement best describes the effect of a hydroxyl group (OH-) on the boiling point of a substance?

6. Based on the skeletal models shown in Table 7.2, which of the following images shows the skeletal model for hexanol?

7. Organic chemists draw skeletal models to simplify the actual atoms and connections that exist within a molecule. Each short line segment represents the connection between two carbon atoms. In alkane molecules, hydrogen atoms surround each carbon atom in such a way that there are three hydrogen atoms on each end carbon and two hydrogen atoms on each middle carbon. These molecules can also be represented by ball-and-stick models or chemical formulas. An example for the molecule hexane is shown in Figure 7.5.


Figure 7.5

The alkane molecule, decane, has the following skeletal structure.

What is the chemical formula for decane?

8. Decane has a molar mass of 142 g/mol. What could a person expect its boiling point to be?

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