5.1 Formula Mass – Introduction To Chemistry

Home » What Is The Formula Mass » 5.1 Formula Mass – Introduction To Chemistry

Maybe your like

Formula Mass for Covalent Substances

For covalent substances, the formula represents the numbers and types of atoms composing a single molecule of the substance; therefore, the formula mass is sometimes referred to as a molecular mass.

Consider chloroform (CHCl3), a covalent compound once used as a surgical anesthetic and now primarily used in the production of the “anti-stick” polymer, Teflon. The molecular formula of chloroform indicates that a single molecule contains one carbon atom, one hydrogen atom, and three chlorine atoms. The average molecular mass of a chloroform molecule is therefore equal to the sum of the average atomic masses of these atoms. Figure 1 outlines the calculations used to derive the molecular mass of chloroform, which is 119.377 amu.

1 C mass = 12.011 amu
1 H masses = 1.00794 amu
3 Cl masses = 3 x 35.4527 amu = 106.3581
Total = 119.377 amu = the molecular mass of CHCl3
Figure 1. The average mass of a chloroform molecule, CHCl3, is 119.377 amt, which is the sum of the average atomic masses of each of its constituent atoms. The molecular structure of chloroform.

Likewise, the molecular mass of an aspirin molecule, C9H8O4, is the sum of the atomic masses of nine carbon atoms, eight hydrogen atoms, and four oxygen atoms, which amounts to 180.15 amu (Figure 2).

9 C mass = 9 x 12.011 amu = 108.099 amu
8 H masses = 8 x 1.00794 amu = 8.06352 amu
4 O masses = 4 x 15.9994 amu = 63.9976 amu
Total = 180.160 amu = the molecular mass of C9H8O4 
Figure 2. The average mass of an aspirin molecule is 180.160 amu. The molecular structure of aspirin.

Example 1

Ibuprofen, C13H18O2, is a popular non-steroidal anti-inflammatory compound (NSAID). What is the formula mass for this compound?

Solution Molecules of this compound are comprised of 13 carbon atoms, 18 hydrogen atoms, and 2 oxygen atoms. Following the approach described above, the average molecular mass for this compound is therefore:

13 C mass = 13 x 12.011 amu = 156.143 amu
18 H masses = 18 x 1.00794 amu = 18.14292 amu
2 O masses = 2 x 15.9994 amu = 31.9988 amu
Total = 206.285 amu = the molecular mass of C13H18O2 

Test Yourself Acetaminophen, C8H9NO2, is the active ingredient in Tylenol. What is the molecular mass for this compound?

Answer

151.16 amu

Tag » What Is The Formula Mass