Chapter 3-6

Chapter 6 – Empirical Formulas
1.)
a.) 46.5 g Fe
1 mol Fe
55.8 g Fe
0.834 = 1.00
0.834
b.) 63.53 g Fe
1.14
1.14
= 1.00
c.) 61.3 g Mn
1.15
1.15
1 mol Fe
55.8 g Fe
= 0.834 mol Fe
1.66 = 2.00
0.834
= 1.14 mol Fe
1.14
1.14
= 1.00
1 mol Mn = 1.15 mol Mn
54.9 g Mn
= 1.00
1.15
1.15
= 1.00
d.) 26.6 g K
1 mol K
39.1 g K
= 0.680 mol K
38.0 g O
1 mol O
16.0 g O
= 2.38 mol O
0.680 = 1.00
0.680
2.)
a.) 36.5 g Na
38.1 g O
1 mol Na
23.0 g Na
= 1.59 mol Na
1 mol O
16.0 g O
= 2.38 mol O
1.59 = 2
0.791
b.) 32.4 g Na
0.681 = 1.00
0.680
0.791 = 1.00
0.791
1 mol Na
23.0 g Na
= 1.41 mol Na
53.44 g S
1 mol S
32.1 g S
= 1.66 mol S
1 mol S
32.1 g S
= 1.14 mol S
1 mol S
32.1 g S
= 1.15 mol S
FeS2
36.47 g S
FeS
36.9 g S
MnS
35.4 g Cr
2.38 = 3.5
0.680
25.4 g S
2.38 = 3
0.791
22.69 g S
1 mol Cr
52.0 g Cr
= 0.681 mol Cr
K2Cr2O7
1 mol S
32.1 g S
= 0.791 mol Cr
Na2SO3
1 mol S
32.1 g S
= 0.704 mol Cr
45.0 g O
1 mol O
16.0 g O
1.41 = 2
0.704
c.) 29.1 g Na
30.4 g O
1.27
1.25
0.704 = 1.00
0.704
1 mol Na
23.0 g Na
= 1.27 mol Na
1 mol O
16.0 g O
= 1.90 mol O
=1
3.)
a.) 0.608 g N
= 2.81 mol O
1.25
1.25
1 mol N
14.0 g N
0.043 = 1
0.043
2.81 = 4
0.704
40.5 g S
=1
1.90
1.25
= 0.043 mol N
= 1.5
Na2SO4
1 mol S
32.1 g S
= 1.258 mol S
Na2S2O3
1.388 g O 1 mol O
16.0 g O
= 0.087 mol O
NO2
0.087 = 2
0.043
Empirical formula wt = (14 + 32) = 46.0 g Therefore, 92 g/25 g = 2
The Molecular formula is 2 x NO2
4.)
a.) 56.4 g P
1.82
1.82
1 mol P
31.0 g P
=1
= 1.82 mol P
2.73
1.82
= 1.5
N2O4
43.7 g O
1 mol O
16.0 g O
= 2.73 mol O
P2O3
Empirical formula wt = P2O3 = 62 g +48 g = 110 g 220 g/110 g = 2
The molecular formula is P4O6
b.) 43.6 g P
1.41
1.41
1 mol P
31.0 g P
=1
= 1.41 mol P
3.53
1.41
= 2.5
56.4 g O
P2O5
1 mol O
16.0 g O
= 3.53 mol O
Empirical formula wt = P2O5 = 142 g then 284 g/142 g = 2
The molecular formula is P4O10
5.)a)
1.62 g CoCl2 xH2O
-.88 g CoCl2
0.74 g H2O
0.88 g CoCl2
b.)
1 mol CoCl2 = 0.00677 mol CoCl2
130 g CoCl2
0.00677
=1
0.00677
1.19 g Pb(C2H3O2)2 xH2O
-1.03 g Pb(C2H3O2)2
0.16 g H2O
1.03 g Pb(C2H3O2)2 1 mol Pb(C2H3O2)2
325 g CoCl2
0.00317
0.00317
c.) 0.61 g NiSO4
0.00394
0.00394
d.) 0.99 g CaSO4
0.00727
0.00727
6.)
a.) 40.2 g K
32.9 g O
=6
= .00317 mol Pb(C2H3O2)2
=1
0.00888
0.00317
1 mol NiSO4
154.5 g NiSO4
=1
1 mol K
39.1 g K
= 1.03 mol K
1 mol O
= 2.05 mol O
0.16 g H2O
1 mol H2O = .00888 mol H2O
18.0 g H2O
Pb(C2H3O2)2 3H2O
0.43 g H2O 1 mol H2O = 0.0239 mol H2O
18.0 g H2O
= 6.06
= 0.00727 mol
0.0150
0.00727
CoCl2 6H2O
= 2.8
= 0.00394 mol
0.0239
0.00394
1 mol CaSO4
136.2 g CaSO4
=1
0.0411
0.00677
0.74 g H2O 1 mol H2O = 0.0411 mol H2O
18.0 g H2O
NiSO4 6H2O
0.27 g H2O 1 mol H2O = 0.0150 mol H2O
18.0 g H2O
CaSO4 2H2O
=2
26.9 g Cr
1 mol Cr
52.0 g Cr
= 0.517 mol Cr
16.0 g O
1.03 = 1.99
0.517
b.) 21.8 g Mg
50.3 g O
0.517 = 1
0.517
1 mol Mg = 0.897 mol Mg
24.3 g Mg
1 mol O
16.0 g O
0.897 = 1
0.897
0.517 = 1
0.897
1 mol Sr
87.6 g Sr
= 0.750 mol Sr
23.9 g O
1 mol O
16.0 g O
= 1.99 mol O
0.750 = 2.02
0.370 = 1
0.370
0.370
d.) 34.58 g Na 1 mol Na = 1.50 mol Na
23.0 g Na
1 mol O
16.0 g O
1.50 = 1.94
0.754
8.)
13.90 g Mg
27.9 g P
K2CrO4
1 mol P
31.0 g P
= 0.900 mol P
= 3.14 mol O
c.) 65.7 g Sr
42.12 g O
2.05 = 3.97
0.517
Mg2P2O7
3.14 = 3.5
0.897
10.4 g Si
1 mol Si
28.1 g Si
= 0.370 mol Si
Sr2SiO4
1.99 = 4.03
0.370
23.3 g P
1 mol P
= 0.754 mol P
31.0 g P
= 2.63 mol O
0.754 = 1
0.754
2.63 = 3.4
0.754
1 mol Mg
24.3 g Mg
= 0.572 mol Mg
17.74 g P
4.01 g H
1 mol H
1.01 g H
= 3.97 mol H
64.30 g O 1 mol O
16.0 g O
31.3 g H2O
1 mol H2O
1.01 g H2O
= 1.72 mol H2O
1 mol P
31.0 g P
Na4P2O7
= 0.573 mol P
= 4.01 mol O
0.572 = 1
0.572
1.72 = 3
0.572
9.)
Formula mass = 268
0.573 = 1
0.572
3.97 = 7
0.572
4.01 = 7
0.572
MgHPO4 3H2O
46.9 % Water
17.18 g Na
1 mol Na
23.0 g Na
= 0.747 mol Mg
11.57 g P
1 mol P
31.0 g P
= 0.373 mol P
5.60 g H
1 mol H
1.01 g H
= 5.54 mol H
65.7 g O
1 mol O
16.0 g O
= 4.11 mol O
46.9 g H2O
1 mol H2O
1.01 g H2O
0.373 = 1
0.373
2.60 = 7
0.373
= 2.6 mol H2O
0.747 = 2
0.373
5.54 = 15
0.373
Na2HPO2 7H2O
4.11 = 11
0.373