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.

5. According to Table 1 and Figure 1 , the molecular mass of CF4 is closest to the molecular mass of which of the following compounds ?

Answer and Explanation

Your Answer is

Correct Answer is A

Explanation

The atomic mass of an F atom can be calculated through table 1: the molecular mass of CHF3 is 70, the molecular mass of CH2F2 is 52, CH2F2 has one more H atom and one less F atom than CHF3, so the atomic mass of F should be equal to 70 -52+1=19.

So the molecular mass of CF4 should be 70-1+19=88. So according to table 1, the closest molecular mass to CF4 should be chloromethane