Passage I

Table 1 lists the name, chemical formula, molecular mass (the mass of 1 molecule in atomic mass units, amu), and BP (the boiling point at 1 atmosphere of pressure) of various compounds. The first compound listed is composed of the elements carbon (C) and hydrogen (H). Each of the other compounds is composed of C, H, and either fluorine (F), chlorine (Cl), bromine (Br), or iodine (I). The elements F, Cl, Br, and I belong to the halogen family.

Table 1 adapted from W. M. Haynes, ed., CRC Handbook of Chemistry and Physics on CD-ROM, Version 2011. @2011 by CRC Press. LLC.

Figure 1 shows a plot of BP versus molecular mass for 3 groups of compounds (Groups 1-3). Each compound in each group is composed of C and 1 or more halogens.

Figure 1 adapted from Michael Laing, "Boiling Points of the Family of Small Molecules, CHwFxClyBrz: How Are They Related to Molecular Mass?" @2001 by Division of Chemical Education, Inc., American Chemical Society.

3. According to Table 1, the relationship between molecular mass and BP among the compounds CHCl3, CHBr3, and CHI3 is best represented by which of the following graphs ?

Answer and Explanation

Your Answer is

Correct Answer is A

Explanation

Looking at table 1, the molecular mass of CHCl3 is the smallest, with a BP of 61; the molecular mass of CHBr3 is in the middle, with a BP of 149; the molecular mass of CHI3 is the largest, with a BP of 218. Therefore, it can be judged that as the molecular mass increases, BP also increases. Then it should be a rising graph line, you can only choose A