Chemical Calculations And Chemical Formulas Worksheets With Answer Key Page 14
ADVERTISEMENT
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20130
Study Guide for An Introduction to Chemistry
69. Lindane is one of the chlorinated pesticides the use of which is now restricted in the United
States. It is 24.78% carbon, 2.08% hydrogen, and 73.14% chlorine and has a molecular mass
of 290.830. What is lindane’s molecular formula? (Obj 18)
1 mol C
? mol C = 24.78 g C
= 2.063 mol C ÷ 2.063 = 1 mol C
12.011 g C
1 mol H
? mol H = 2.08 g H
= 2.064 mol H ÷ 2.063 1 mol H
1.00794 g H
1 mol Cl
? mol Cl = 73.14 g Cl
= 2.063 mol Cl ÷ 2.063 = 1 mol Cl
35.4527 g Cl
Empirical Formula CHCl
molecular mass
290.830
n =
=
6
empirical formula mass
48.472
Molecular Formula = (CHCl)
or
C
H
Cl
6
6
6
6
71. Melamine is a compound used to make the melamine-formaldehyde resins in very hard
®
surface materials such as Formica
. It is 28.57% carbon, 4.80% hydrogen, and 66.63%
nitrogen and has a molecular mass of 126.121. What is melamine’s molecular formula?
(Obj 18)
1 mol C
? mol C = 28.57 g C
= 2.379 mol C ÷ 2.379 = 1 mol C
12.011 g C
1 mol H
? mol H = 4.80 g H
= 4.76 mol H ÷ 2.379 2 mol H
1.00794 g H
1 mol N
? mol N = 66.63 g N
= 4.757 mol N ÷ 2.379 2 mol N
14.0067 g N
Empirical Formula CH
N
2
2
molecular mass
126.121
n =
=
3
empirical formula mass
42.040
Molecular Formula = (CH
N
)
or C
H
N
2
2
3
3
6
6
Additional Problems
73. Your boss at the hardware store points you to a bin of screws and asks you to find out the
approximate number of screws it contains. You weigh the screws and find that their total
mass is 68 pounds. You take out 100 screws and weigh them individually, and you find that 7
screws weigh 2.65 g, 4 screws weigh 2.75 g, and 89 screws weigh 2.90 g. Calculate the
weighted average mass of each screw. How many screws are in the bin? How many gross of
screws are in the bin?
weighted average = 0.07(2.65 g) + 0.04(2.75 g) + 0.89(2.90 g) = 2.88 g
453.6 g
1 screw
=
4
? screws = 68 lb screws
1.1 x 10 screws
1 lb
2.88 g
453.6 g
1 screw
1 gross screws
? screws = 68 lb screws
=
74 gross screws
1 lb
2.88 g
144 screws
ADVERTISEMENT
0 votes
Related Articles
Related forms
Related Categories
Parent category: Education