b. Example 2. What is the GMW of H2SO4?
Solution. Notice in this problem that the subscripts apply to the hydrogen and
oxygen atoms. In this problem, we must multiply these elements by their corresponding
subscript to obtain the correct GMW for this molecule.
1.0 X 2 =
32.1 X 1 = 32.1
16.0 X 4 = + 64.0
c. Example 3. What is the GMW of (NH4)2CO3.3H2O?
Solution. In this problem, the NH4 radical is enclosed by parentheses and a
subscript of two is assigned. In this situation, all elements contained within the
parentheses are multiplied by two. Also, the hydrogen atom of the NH4 radical has a
subscript of four. Therefore, the total number of hydrogens present are eight. The
attached water of hydration has a coefficient of three. This must be considered, and
each individual atom within the water molecule must be multiplied by a coefficient of
three in addition to any subscripts.
14.0 X 2 = 28.0
1.0 X 8 =
12.0 X 1 = 12.0
16.0 X 3 = 48.0
1.0 X 6 =
16.0 X 3 = + 48.0
MOLES AND GRAM MOLECULAR WEIGHT
Remember from the discussion on moles that a mole of any substance is the
number of grams proportional to the atomic or molecular weight of the substance. If this
is true, then one mole of NaCl weighs 58.5 grams. One mole of any substance has a
mass equal to one gram molecular weight of that substance.