ACT science practice test 34

Directions: Each passage is followed by several questions. After reading a passage, choose the best answer to each question and fill in the corresponding oval on your answer document. You may refer to the passages as often as necessary.

You are NOT permitted to use a calculator on this test.


As a liquid evaporates, the vapors on the surface of the liquid exert a vapor pressure. Vapor pressure varies with the liquid's temperature.

When vapor pressure equals the surrounding atmospheric pressure, boiling occurs. The normal boiling point of a liquid is defined as the temperature at which vapor pressure is equal to the standard atmospheric pressure of 760 mmHg (1 atm). If atmospheric pressure changes, a liquid's boiling point will also change.

Figure 4.3 illustrates the relationship between vapor pressure and temperature for four organic compounds belonging to the alkane group. The normal boiling point is indicated by a horizontal dashed line.

Figure 4.3

Source: http://wiki.chemprime.chemeddl.org.

Organic compounds are composed of various functional groups attached to a hydrocarbon backbone. A functional group is a specific grouping of atoms that exhibits a characteristic set of properties. These properties remain consistent, regardless of the overall size of the compound.

Figure 4.4 compares the normal boiling points of organic compounds of increasing size for eight different functional groups, including the alkane group.

Figure 4.4

Table 4.1 lists the types of chemical bonds each of the eight functional groups are capable of forming. Stronger bonds are more difficult to break, thus requiring a higher temperature for phase changes.

TABLE 4.1 Functional Group Bonds

Table 4.2 lists characteristics of four common organic compounds with similar molecular weights. The temperatures listed represent the normal boiling point for each molecule.

TABLE 4.2 Molecular Weight

1. A compound's normal boiling point is the:

A. minimum temperature at which the compound boils.
B. average temperature at which the compound boils across all possible atmospheric pressures.
C. maximum temperature at which the compound boils.
D. temperature at which the compound boils under standard atmospheric pressure.

2. According to Figure 4.3, an organic compound will boil at a lower temperature if:

A. vapor pressure increases.
B. atmospheric pressure decreases.
C. atmospheric and vapor pressures become unequal.
D. vapor pressure is greater than atmospheric pressure.

3. At a vapor pressure of 50 mmHg, which alkane in Figure 4.3 would boil closest to 0°C?

A. Heptane
B. Hexane
C. Pentane
D. Octane

4. According to Figure 4.3, what vapor pressure will cause pentane's boiling point to be closest to 40°C?

A. 760 mmHg
B. 600 mmHg
C. 400 mmHg
D. 850 mmHg

5. What is the best approximation for the normal boiling point of octane in Figure 4.3?

A. 126°C
B. 100°C
C. 145°C
D. 98°C

6. According to Figure 4.4, the alkanes exhibit normal boiling points most similar to which other group?

A. Alkynes
B. Alcohols
C. Carboxylic acids
D. Amines

7. Based on the data in Figure 4.4, a 2-carbon alcohol would exhibit a normal boiling point closest to that of a:

A. 3-carbon alkane.
B. 9-carbon alkene.
C. 4-carbon ketone.
D. 2-carbon carboxylic acid.

8. Based on the data in Figure 4.4, which type of bond listed in Table 4.1 is the weakest?

A. Dipole-dipole
B. Double hydrogen
C. Van der Waals
D. Single hydrogen

9. Caproic acid is a carboxylic acid with a molecular formula of C6H12O2. Which of the following temperatures is closest to the normal boiling point of caproic acid?

A. 200°C
B. 250°C
C. 100°C
D. 125°C

10. Based on the data in Figure 4.4, which of the following lists the bonds in Table 4.1 from the highest to the lowest boiling point required to break them?

A. Van der Waals, dipole-dipole, single hydrogen, double hydrogen
B. Double hydrogen, single hydrogen, dipole-dipole, Van der Waals
C. Single hydrogen, double hydrogen, dipole-dipole, Van der Waals
D. Dipole-dipole, Van der Waals, single hydrogen, double hydrogen

11. Which of the following generalizations about the relationship between an organic compound's molecular weight and its boiling point is best supported by the data in Table 4.2?

A. The boiling point varies directly with molecular weight.
B. As molecular weight increases, the boiling point decreases.
C. As molecular weight decreases, the boiling point increases.
D. The boiling point is not determined by molecular weight.

12. Based on the data in Figure 4.4, n-Butanol (see Table 4.2) most likely contains which functional group?

A. Alcohol
B. Ester
C. Amine
D. Alkyne

13. Which of the four compounds in Table 4.2 is most likely to contain double hydrogen bonds?

A. Pentane
B. Butanone
C. Propanoic acid
D. n-Butanol

14. Based on the information in the passage, which of the following can be inferred about the type of bonds in an organic compound?

A. Double hydrogen bonds are easier to break at high temperatures than single hydrogen bonds.
B. Dipole-dipole bonds require the highest boiling point to break of all four types of bonds.
C. Van der Waals bonds become easier to break as a compound's vapor pressure is increased.
D. At the same vapor pressure, single hydrogen bonds require a higher boiling point to break than dipole-dipole bonds.

15. Which of the following generalizations is best supported by the data in Figures 4.3 and 4.4?

A. Organic compounds containing the same number of carbon atoms have similar boiling points.
B. The boiling point increases with the number of carbon atoms among organic compounds within the same group.
C. The number of carbon atoms in an organic compound cannot be used to predict the compound's relative boiling point.
D. The greater the number of carbon atoms in an organic compound, the lower that compound's boiling point is.