CHE 107
TUTORIAL QUESTIONS
1. A 0.455 g sample of magnesium is allowed to burn in 2.315 g of oxygen gas. The sole
product is magnesium oxide. After the reaction, no magnesium remains and the mass of
unreacted oxygen is 2.015 g. What mass of magnesium oxide is produced?
2. A 0.382 g sample of magnesium is allowed to react with 2.652 g of nitrogen gas. The sole
product is magnesium nitride. After the reaction, the mass of unreacted nitrogen is 2.505 g.
What mass of magnesium nitride is produced?
3. A 7.12 g sample of magnesium is heated with 1.80 g of bromine. All the bromine is used
up, and 2.07 g of magnesium bromide is the only product. What mass of magnesium remains
unreacted?
4. A 1.446 g sample of potassium reacts with 8.178 g of chlorine to produce potassium
chloride as the only product. After the reaction, 6.867 g of chlorine remains unreacted. What
mass of potassium chloride was formed?
5. Within the limits of experimental error, show that the law of conservation of mass was
obeyed in the following experiment: 10.00 g calcium carbonate (found in limestone) was
dissolved in 100.0 mL hydrochloric acid (d = 1.148 g/mL). The products were 120.40 g
solution (a mixture of hydrochloric acid and calcium chloride) and 2.22 L carbon dioxide gas
(d = 1.9769 g/L)
6. When 0.455 g of magnesium reacted with 2.315 g of oxygen, 0.755 g of magnesium oxide
was obtained.
a) Determine the mass of magnesium contained in a 0.500 g sample of magnesium oxide.
b) What masses of magnesium and oxygen must be combined to make exactly 2.000 g of
magnesium oxide?
c) What substances are present, and what are their masses, after the reaction of 10.00 g of
magnesium and 10.00 g of oxygen?
7. Samples of pure carbon weighing 3.62, 5.91, and 7.07 g were burned in an excess of air.
The masses of carbon dioxide obtained (the sole product in each case) were 13.26, 21.66, and
25.91 g, respectively.
(a) Do these data establish that carbon dioxide has a fixed composition?
(b) What is the composition of carbon dioxide, expressed in % C and % O, by mass?
8. Sulfur forms two compounds with oxygen. In the first compound, 1.000 g sulfur is
combined with 0.998 g oxygen, and in the second, 1.000 g sulfur is combined with 1.497 g
oxygen. Show that these results are consistent with Dalton’s law of multiple proportions
9. The following data were obtained for compounds of nitrogen and hydrogen
Compound
Mass of Nitrogen/ g
Mass of Hydrogen/g
A
0.500
0.108
B
1.000
0.072
C
0.750
0.108
a) Show that these data are consistent with the law of multiple proportions.
(b) If the formula of compound B is N2H2. what are the formulas of compounds A and C?
TUTORIAL 2
1. The atomic masses of 35Cl (75.53 percent) and 37Cl (24.47 percent) are 34.968 amu and
36.956 amu, respectively. Calculate the average atomic mass of chlorine. The percentages in
parentheses denote the relative abundances.
2. The atomic masses of 6Li and 7Li are 6.0151 amu and 7.0160 amu, respectively. Calculate
the natural abundances of these two isotopes. The average atomic mass of Li is 6.941 amu.
3. Which of the following has a greater mass: 2 atoms of lead or 5.1 X 10-23 mole of helium.
4. Hydrogen and chlorine atoms react to form simple diatomic molecules in a 1:1 ratio, that
is, HCl. The natural abundances of the chlorine isotopes are 75.77% and 24.23% The natural
abundances of 2H and 3H are 0.015% and less than 0.001%, respectively.
(a) How many different HCl molecules are possible, and what are their mass numbers (that is,
the sum of the mass numbers of the H and Cl atoms)?
(b) Which is the most abundant of the possible HCl molecules? Which is the second most
abundant?
5. Carbon has two stable isotopes, 12C and 13C, and fluorine has only one stable isotope, 19F.
How many peaks would you observe in the mass spectrum of the positive ion of CF4+?
Assume that the ion does not break up into smaller fragments.
6. How many nitrate ions, and how many oxygen atoms are present in of magnesium nitrate,
Mg(NO3)2?
7. If 1.0µL sample of liquid ethyl mercaptan is allowed to evaporate and distribute itself
throughout a chemistry lecture room with dimensions 65 ft × 35 ft × 14 ft, will the odor of
the vapor be detectable in the room? The limit of detectability is 9 ×10-4 µmol/m3. The
density of liquid ethyl mercaptan is 0.84 g/mL.
8. How many milliliters of halothane would contain 1.00× 1024 Br atoms? (d= 1.871 g/mL).
9. For many years chloroform (CHCl3) was used as an inhalation anesthetic in spite of the
fact that it is also a toxic substance that may cause severe liver, kidney, and heart damage.
Calculate the percent composition by mass of this compound.
10. Cinnamic alcohol is used mainly in perfumery, particularly in soaps and cosmetics. Its
molecular formula is C9H10O. (a) Calculate the percent composition by mass of C, H, and O
in cinnamic alcohol. (b) How many molecules of cinnamic alcohol are contained in a sample
of mass 0.469 g?