Given the two amounts of starting materials, you discover that you can make a maximum of
0.125 mole of Ba 3 (AsO 4 ) 2 , because at that point you will have exhausted your supply of
K 3 AsO 4.
- A test tube containing CaCO 3 is heated until all of the compound decomposes. If the test
tube plus calcium carbonate originally weighed 30.08 grams and the loss of mass during
the experiment was 4.400 grams, what was the mass of the empty test tube?
A. 20.07 g
B. 21.00 g
C. 24.50 g
D. 25.08 g
E. 25.68 gAnswer: A
Begin by writing a balanced equation. Remember that all Group II carbonates decompose to
yield the metallic oxide plus carbon dioxide gas.
CaCO 32 ^^ssghh"CaO +CO _ iAccording to your balanced equation, any loss of mass during the experiment would have to
have come from the carbon dioxide gas leaving the test tube. 4.400 grams of CO 2 gas corre-
spond to 0.1000 mole. Because all of the calcium carbonate decomposed, and the calcium car-
bonate and carbon dioxide gas are in a 1:1 molar ratio, you must originally have had 0.1000
mole of calcium carbonate, or 10.01 grams. The calcium carbonate and test tube weighed
30.08 grams, so if you get rid of the calcium carbonate, you are left with 20.07 grams for the
empty test tube.
- 32.0 grams of oxygen gas, 32.0 grams of methane gas, and 32.0 grams of sulfur dioxide
gas are mixed. What is the mole fraction of the oxygen gas?
A. 0.143
B. 0.286
C. 0.333
D. 0.572
E. 0.666Answer: B
Gravimetrics