CHEM 1305-Home-work 8 NAME:
1) What is the molar mass of crotonaldehyde (C
4
H
6
O)?
A) 54.1 g/mol B) 57.10 g/mol C) 64.0 g/mol D) 70.0 g/mol
2) The formula mass of (NH
4
)
3
PO
4
, is ________.
A) 121.12 amu B) 149.12 amu C) 110.12 amu D) 159.68 amu E) 172.42 amu
3) The mass percentage of Cl in the compound KClO
3
is ________.
A) 53.87% B) 64.19% C) 33.33% D) 36.51% E) 28.93%
4) A 2.00 g sample of cholesterol contains 1.68 g C, 0.24 g H, and 0.080 g O. What is the percent
composition of C in cholesterol?
A) 76% B) 91% C) 84% D) 56% E) 4.0%
5) How many Cl atoms are present in 2.16 moles of NCl
3
?
A) 2.4

10 22 Cl atoms B) 8.4

10 24 Cl atoms C) 3.90

10 24 Cl atoms
D) 6.6

10

26 Cl atoms E) 4.33

10 23 Cl atoms
6) Calculate the mass (grams) of 0.750 moles of Al
2
(Cr
2
O
7
)
3
:
A) 270.0 g B) 486.0 g C) 809.9 g D) 526 g E) 702.0 g
7) Calculate the number of iron atoms in 6.98

10

3 grams of iron.
A) 9.37

10 28 atoms B) 3.92

10 19 atoms C) 3.24

10 23 atoms
D) 5.54

10 20 atoms E) 7.53

10 19 atoms
8) A thimble of water contains 4.0 x 10 21 molecules. The number of moles of H
2
O is:
A) 2.4 x 10 45 B) 6.6 x 10 -3 C) 6.6 x 10 -23 D) 2.4 x 10 23
9) Which quantity contains Avogadro’s number of molecules?
A) 8.8 g CO
2
B) 34 g of NH
3
C) 9 g of H
2
O D) 98 g of H
2
SO
4
10) A beaker contains 0.964 grams of nitrogen. How many moles of molecular nitrogen does the beaker
contain?
A) 0.0688 mol B) 2.262

10 23 mol C) 0.0344 mol D) 2.64 mol E) 29.07 mol
11) How many grams of carbon are present in 26.2 grams of H
2
CO
3
?
A) 11.60 g B) 16.8 g C) 47.3 g D) 5.07 g E) 23.9 g
12) 2.00 formula units of the compound K
2
S contains ________.
A) 4 K atoms B) 2.00 moles of S atoms C) 2.00 grams of K
2
S
D) 39.09 g of K E) 110.25 grams of K
2
S
13) The “set-up” for the problem “What is the mass, in grams, of 2.50

10 22 atoms of Ca?” which follows is correct, except numbers in the last conversion factor have been replaced by the letters A and B.
What are the numerical values of A and B, respectively?
 22
atoms Ca




1 mol Ca A Ca
B Ca


A) 1 mole and 6.02

10 23 atoms B) 40.08 g and 1 mol C) 6.02

10 23 g and 1 atom
D) 40.08 mol and 6.02

10 23 atoms E) 6.02

10 23 atoms and 40.08 g
14) Which of the following is the correct “set-up” for the problem “How many grams of S are present in
50.0 g of S
4
N
4
?”

A)
50.0 g S N
4



1 mole S N
4
 184.32 g S N
4
 
 
4 moles S
1 mole S N
4

32.07 g S
4 moles S


B)
50.0 g S N
4



1 mole S N
4
184.32 g S N
4
4 moles S
1 mole S N
4
 
32.07 g S
1 mole S


C)
50.0 g S N
4



1 mole S N
4
184.32 g S N
4
1 mole S
1 mole S N
4
 
32.07 g S
1 mole S


D)
50.0 g S N
4



1 mole S N
4
184.32 g S N
4
15) The empirical formula of C
10
H
20
is:
1 mole S
4 moles S N
4
32.07 g S
1 mole S

A) C
10
H
20
B) C
5
H
10
C) C
2
H
4
D) CH
16) What is the empirical formula of a compound that contains 78.11% B and 21.89% H?
2
A) BH
2
B) BH
3
C) B
2
H
6
D) B
2
H
3
E) BH
17) The empirical formula of a compound is CH
2
O and its formula weight is 120.12 amu. What is the
molecular formula?
A) C
2
H
4
O
2
B) C
3
H
6
O
3
C) C
4
H
8
O
4
D) C
5
H
10
O
5
E) C
6
H
12
O
6
18) Analysis of an unknown nickel oxide compound indicated that the molar ratio of nickel to oxygen was
0.167 to 0.251, respectively. What is the empirical formula for the compound?
A) Ni
3
O
4
B) NiO C) NiO
3
D) Ni
2
O
3
E) Ni
2
O
19) Determine the empirical and molecular formulas for caffeine, a stimulant found in coffee and soda, given the following percent composition: 49.5 % carbon, 5.15 % hydrogen, 28.9 % nitrogen, and 16.5 % oxygen. The molecular weight of this compound is approximately 195 g/mol.