1. The percent by mass of nitrogen in Mg(CN)2 is equal to
1)
3)
2)
4)
2. A compound consists of 40.% sulfur and 60.% oxygen
by mass. What is the empirical formula of this
compound?
1) SO
2) SO2
3) SO3
4) SO4
3. What is the empirical formula of a compound if a sample
contains 8.52 grams of carbon and 1.42 grams of
hydrogen?
1) C2H
2) CH2
3) CH
4) C2H2
4. If the density of a gas at STP is 2.50 grams per liter, what
is the gram molecular mass of the gas?
1) 2.50
3) 56.0
2) 22.4
4) 89.6
5. Air consists of approximately 79% nitrogen and 19%
oxygen. Which gas is less dense than air at STP?
1) CO2
2) H2S
3) NH3
4) SO2
6. What is the molecular formula of a compound with an
empirical formula of CH and a molecular mass of 78?
1) C6H6
2) C4H10
3) C2H2
4) CH
7. A student determining the percent by mass of water in a
hydrated crystal obtained the following data.
Mass of crystal before heating..................5.0 g
Mass of crystal after 1st heating...............4.0 g
Mass of crystal after 2nd heating..............4.0 g
What is the percent by mass of water hydrate?
1) 0.80%
3) 80.%
2) 0.20%
4) 20.%
8. The percent by mass of carbon in HC2H3O2 is equal to
3)
1)
2)
4)
9. What is the percent by mass of oxygen in Ca(OH)2
[formula mass = 47.1]
1) 21.6%
3) 45.9%
2) 43.2%
4) 54.1%
10. The percent by mass of nitrogen in N2O is
1) 8.0
3) 32
2) 16
4) 64
11. A compound contains 50% sulfur and 50% oxygen by
mass. The empirical formula of this compound is
1) SO
2) SO2
3) SO3
4) SO4
12. What is the molecular mass of a gas whose density is
1.25 grams per liter at STP?
1) 14.0
3) 20.0
2) 17.9
4) 28.0
13. An 8.24-gram sample of a hydrated salt is heated until it
has a constant mass of 6.20 grams. What was the percent
by mass of water contained in the original sample?
1) 14.1%
3) 32.9%
2) 24.8%
4) 75.2%
14. A 60. gram sample of LiCl • H2O is heated in an open
crucible until all of the water has been driven off. What
is the total mass of LiCl remaining in the crucible?
1) 18 g
3) 42 g
2) 24 g
4) 60 g
15. What is the empirical formula of a compound that
contains 30.4% nitrogen and 69.6% oxygen by mass?
1) NO
2) NO2
3) N2O3
4) N2O5
16. What is the percent by mass of hydrogen in CH3COOH
(formula mass = 60.)?
1) 1.7%
3) 6.7%
2) 5.0%
4) 7.1%
17. A 1.20-gram sample of a hydrated salt is heated to a
constant mass of 0.80 gram. What was the percent by
mass of water contained in the original sample?
1) 20.
3) 50.
2) 33
4) 67
18. A compound contains 16% carbon and 84% sulfur by
mass. What is the empirical formula of this compound?
1) CS2
2) C2S2
3) CS
4) C2S
19. A hydrated salt is a solid that includes water molecules
within its crystal structure. A student heated a 9.10-gram
sample of a hydrated salt to a constant mass of 5.41
grams. What percent by mass of water did the salt
contain?
1) 3.69%
3) 40.5%
2) 16.8%
4) 59.5%
20. What is the empirical formula of a compound consisting
of 29.6% oxygen and 70.4% fluorine by mass?
1) OF
2) OF2
3) O2F
4) O2F4
21. What is the molecular formula of a compound that has a
molecular mass of 92 and an empirical formula of NO2?
1) NO2
2) N2O4
3) N3O6
4) N4O8
22. A sample of an unknown gas at STP has a density of
1.25 grams per liter. What is the gram molecular mass of
this gas?
1) 28.0 g
3) 64.0 g
2) 44.0 g
4) 80.0 g
23. A compound has an empirical formula of CH2 and a
molecular mass of 56. What is its molecular formula?
1) CH2
2) C2H4
3) C3H6
4) C4H8
24. The empirical formula of a compound is CH2O and the
molecular mass is 180. What is the molecular formula of
this compound?
1) C6H12O6
2) C4H8O4
3) C2H4O2
4) CH2O
25. What is the percent by mass of nitrogen in the compound
NH4NO3 (formula mass = 80.)?
1) 5.7%
3) 29%
2) 18%
4) 35%
26. Which of the following gases has the greatest density at
STP?
1) SO2
2) CO2
3) Cl2
4) N2
27. What is the gram-molecular mass of a gas that has a
density of 1.78 grams per liter at STP?
1) 17.8 g
3) 39.9 g
2) 22.4 g
4) 79.6 g
28. A compound consists of 25.9% nitrogen and 74.1%
oxygen by mass. What is the empirical formula of the
compound?
1) NO
2) NO2
3) N2O
4) N2O5
29. Base your answer to the following question on the table
below shows the data collected during the heating of a
5.0 gram sample of a hydrated salt.
30.
31.
32.
33.
34.
35.
After 60. minutes, how many grams of water appear to
remain in the salt?
1) 0.00
3) 1.9
2) 2.0
4) 0.90
What is the empirical formula of a compound that
contains 85% Ag and 15% F by mass?
1) AgF
2) Ag2F
3) AgF2
4) Ag2F2
In which compound is the percent by mass of oxygen
greatest?
1) BeO
3) CaO
2) MgO
4) SrO
What is the percent by mass of sulfur in sulfur dioxide?
1) 32
3) 50.
2) 33
4) 67
A compound has the empirical formula CH and a
molecular mass of 78. What is the molecular formula of
the compound?
1) C2H2
2) C3H3
3) C4H4
4) C6H6
What is the percent by mass of oxygen in H2SO4?
[formula mass = 98]
1) 16%
3) 65%
2) 33%
4) 98%
The percent by mass of oxygen in H2C2O4 is equal to
1)
3)
2)
4)
36. A compound which contains 75% carbon and 25%
hydrogen by mass has the formula
1) CH4
2) C2H2
3) C2H6
4) C3H8
37. Eleven grams of a gas occupies 5.6 liters at STP. What is
the molecular mass of this gas?
1) 11
3) 44
2) 22
4) 88
38. A compound was analyzed and found to contain 75%
carbon and 25% hydrogen by mass. What is the
compound's empirical formula?
1) CH
2) CH2
3) CH3
4) CH4
39. A 4.4 gram sample of a hydrate was heated until the
water of hydration was driven off. The anhydrous
compound remaining had a mass of 3.3 grams. What is
the percentage by mass of water in the hydrate?
1) 25%
3) 67%
2) 33%
4) 75%
40. A 10.0 gram sample of a hydrate was heated until all the
water of hydration was driven off. The mass of
anhydrous product remaining was 8.00 grams. What is
the percent of water in the hydrate?
1) 12.5%
3) 25.0%
2) 20.0%
4) 80.0%
41. At STP, what is the density of a gas that has a gram
molecular mass of 32 grams?
1) 0.70 g/L
3) 3.2 g/L
2) 2.0 g/L
4) 1.4 g/L
42. What is the empirical formula of a compound that
contains 28% iron, 24% sulfur, and 48% oxygen by
mass?
1) FeSO3
2) FeSO4
3) Fe2(SO3)3
4) Fe2(SO4)3
43. The density of a gas is 0.77 gram per liter at STP. What
is the formula mass of the gas?
1) 8.5 g
3) 29 g
2) 17 g
4) 34 g
44. What is the approximate percent composition by mass of
CaBr2 (formula mass = 200)?
1) 20% calcium and 80% bromine
2) 25% calcium and 75% bromine
3) 30% calcium and 70% bromine
4) 35% calcium and 65% bromine
45. What is the ratio by mass of hydrogen to oxygen in H2O?
1) 1:2
3) 1:8
2) 2:1
4) 8:1
46. Which species contains the greatest percent by mass of
hydrogen?
1) OH–
2) H2O
3) H3O+
4) H2O2
47. A hydrate is a compound with water molecules incorporated into its crystal structure. In an experiment to find the percent by mass of
water in a hydrated compound, the following data were recorded:
What is the percent by mass of water in the hydrate?
1) 8.0 %
2) 50. %
48. A student determining the percent by mass of water in a
hydrated sample of salt obtained the following data:
Mass of hydrate 6.25 g
Mass of sample after 1st heating 5.12 g
Mass of sample after 2nd heating 5.12 g
The correct expression for obtaining the percent by mass
of water in the sample is
1)
3)
2)
4)
3) 72. %
4) 96. %
49. A compound contains 53% Al and 47% O by mass. What
is the empirical formula of this compound?
1) AlO
2) AlO2
3) Al2O3
4) Al3O2
50. The percent by mass of oxygen in Na2SO4 (formula mass
= 142) is closest to
1) 11%
3) 45%
2) 22%
4) 64%
Answer Key
1.
3
30.
1
2.
3
31.
1
3.
2
32.
3
4.
3
33.
4
5.
3
34.
3
6.
1
35.
2
7.
4
36.
1
8.
2
37.
3
9.
2
38.
4
10.
4
39.
1
11.
2
40.
2
12.
4
41.
4
13.
2
42.
4
14.
3
43.
2
15.
2
44.
1
16.
3
45.
3
17.
2
46.
3
18.
1
47.
2
19.
3
48.
4
20.
2
49.
3
21.
2
50.
3
22.
1
23.
4
24.
1
25.
4
26.
3
27.
3
28.
4
29.
1