MOLECULAR WEIGHT
A compound is made up of two or more elements combined in a definite ratio that is
represented by a molecular formula. Each of these
... [Show More] elements has a certain atomic
weight, which can be found in the periodic table. The sum of the atomic weights of
the atoms in the molecular formula is called the formula weight or molecular
weight or formula mass. We will use the term molecular weight for this number in our
work. Here are three examples of molecular weight determination:
Ca3(PO4)2
Molecular
Weight = 3 Ca = 3 x 40.08 = 120.24
2 P = 2 x 30.97 = 61.94
8 O = 8 x 16.00 = 128.00
310.1
8
C3H5O2Cl Molecular
Weight = 3 C = 3 x 12.01 = 36.03
5 H = 5 x 1.008 = 5.04
2 O = 2 x 16.00 = 32.00
1 Cl = 1 x 35.45 = 35.45
108.5
2
Al2(SO4)3
Molecular
Weight = 2 Al = 2 x 26.98 = 53.96
3 S = 3 x 32.07 = 96.21
12 O =
12 x
16.00 = 192.00
Problem Set #1
1. Na2SO4 = 142.05
Na = 22.99 x 2 = 45.98
S = 32.07 x 1 = 32.07
O = 16 x 4 = 64
2. O2F2 = 70
O = 16 x 2 = 32
F = 19 x 2 = 38
3. Ca(NO3)2 =164.1
Ca = 40.08 x 1 = 40.08
N = 14.01 x 2 = 28.02
O = 16 x 6 = 96
4. Cl2O7 = 182.9
Cl = 35.45 x 2 = 70.9
O = 16 x 7 = 112
5. K2Cr2O7 = 294.2
K = 39.10 x 2= 78.2
Cr = 52 x 2 = 104
O = 16 x 7 = 112
6. Ca3N2 = 148.26
Ca = 40.08 x 3 = 120.24
N = 14.01 x 2 = 28.02
7. MgI2 = 278.105
Mg = 24.305 x 1 = 24.305
I = 126.9 x 2 = 253.8
8. Li3PO4 = 115.793
Li = 6.941 x 3 = 20.823
P = 30.97 x 1 = 30.97
O = 16 x 4 = 64
9. Fe(OH)3 = 106.874
Fe = 55.85 x 1 = 55.85
O = 16 x 3 = 48
H = 1.008 x 3 = 3.024
10. NH4NO3 = 80.052
N = 14.01 x 1 = 14.01
H = 1.008 x 4 = 4.032
N = 14.01 x 1 = 14.01
O = 16 x 3 = 48
2.2: MOLES
Chemical compounds react with one another in amounts that are based on their
molecular weights; this chemically reactive amount of compound is called a mole.
The number of moles of a substance is equivalent to a certain weight in grams, and it
can be calculated by the following equation.
moles = grams / molecular weight
A chemical compound's weight in grams is equivalent to a certain number of moles of
the substance, and this number can be calculated with the following equation.
Grams = m [Show Less]