Answers___PS_Chapter_6 Moles, Mass, Molecules

Chapter 6:

Calculate the molar Mass the following
1. CH4
C = 1 x 12g/mol = 12 g/mol
H = 4 x 1 g/mol = 4 g/mol
CH4 = 16 g/mol


2. H2O
H = 2 x 1 g/mol = 2 g/mol
O = 1 x 16 g/mol = 16 g/mol
H2O = 18 g/mol

3. MgBr2
Mg = 1 x 24 g/mol = 24 g/mol
Br = 2 x 80 g/mol = 160 g/mol
MgBr2 = 184 g/mol

4. H3PO4
H = 3 x 1 g/mol = 3 g/mol
P = 1 x 31 g/mol = 31 g/mol
O = 4 x 16 g/mol = 64 g /mol
H3PO4 = 98 g/mol

5. Ca(OH)2
Ca = 1 x 40 g/mol = 40 g/mol
O = 2 x 16 g/mol = 32 g/mol
H = 2 x 1 g/mol = 2 g/mol
Ca(OH)2 = 74 g/mol

6 Ca3(PO4)2
Ca = 3 x 40 g/mol = 120 g/mol
P = 2 x 31 g/mol = 62 g/mol
O = 8 x 16 g/mol = 128 g/mol
Ca3(PO4)2 = 310 g/mol




Moles, Mass, Molecules
1. How many grams are contained in 5.0 moles of each of the following?

a. NaOH
Molar Mass Na = 1 x 23g/mol = 23g/mol
O = 1 x 16 g/mol = 16g/mol
H = 1 x 1 g/mol = 1 g/mol
NaOH = 40 g/mol

5.0 moles NaOH x 40 g/mol = 200 g NaOH

, b. N2SO4
Molar Mass N = 2 x 14 g/mol = 28g/mol
S = 1 x 32 g/mol = 32g/mol
O = 4 x 16 g/mol = 64g/mol
N2SO4 = 124 g/mol

5.0 moles N2SO4 x 124 g/mol = 620 g N2SO4

c. H3PO4
Molar Mass H = 3 x 1 g/mol = 3 g/mol
P = 1 x 31 g/mol = 31 g/mol
O = 4 x 16 g//mol = 64 g/mol
H3PO4 = 98 g/mol

5.0 moles H3PO4 x 98 g/mol = 490 g H3PO4

d. Ca3(PO4)2
Molar Mass Ca = 3 x 40 g/mol = 120 g/mol
P = 2 x 31 g/mol = 62 g/mol
O = 8 x 16 g/mol = 128 g/mol
Ca3(PO4)2 = 310 g/mol

5.0 moles Ca3(PO4)2 x 310 g/mol = 1550 g Ca3(PO4)2


2. How many moles are contained in 100 grams of the following?

a. HCl
Molar Mass H = 1 x 1 g/mol = 1 g/mol
Cl = 1 x 35 g/mol = 35 g/mol
HCl = 36 g/mol

100 g HCl x 1 mol/36 g = 2.78 mol

b. Ca(OH)2
Molar Mass Ca = 1 x 40g/mol = 40 g/mol
O = 2 x 16 g/mol = 32 g/mol
H = 2 x 1 g/mo = 2 g/mol
Ca(OH)2 = 74 g/mol

100 g Ca(OH)2 x 1 mol/ 74 g = 1.35 mol
c. KMnO4
Molar Mass K = 1 x 39 g/mol = 39 g/mol
Mn = 1 x 55 g/mol = 55 g/mol
O = 4 x 16 g/mol = 64 g/mol
KMnO4 = 158 g/mol