Chem 20 Stoichiometry Unit Test
Part I: Short Answer. Answer each question using full sentences. Be sure to make as
many points in your answer as the question is worth to receive full marks.
1. What are chemical equation factors? What are they used for? (3 marks)
2. Explain the terms “limiting reagent” and “reagent in excess”. (4 marks)
3. Explain the following terms: (a) actual yield, (b) percentage yield. (4 marks)
Part II: Work-out questions. Show all work and all calculations performed. If you are
unsure of how to explain a step, ask. Include sentences with your answers.
4. Ammonia burns in oxygen in the presence of a platinum catalyst to give off nitrogen
monoxide and water according to the equation
4 NH 3( g )  5O2( g )  4 NO( g )  6 H 2 O( g )
a) How many moles of oxygen are needed to completely react with 6.0 mol of
ammonia? (2 marks)
b) How many moles of nitrogen monoxide will be produced from the complete reaction
of 15.0 mol oxygen gas? (2 marks)
5. Iron Ore, Fe2 O3 , reacts with carbon monoxide to produce iron according to the
equation Fe2 O3( s )  3CO( g )  2 Fe( s )  3CO2( g ) . If 2.00  10 3 kg of iron ore produces
1398 kg of iron and 1652 kg of carbon dioxide, what mass of carbon monoxide must
have been used? Which law is this using? (3 marks)
6. If 12.0 g of barium nitrate is dissolved in water and added to a solution containing
16.0 g of potassium sulfate, a double displacement reaction occurs:
Ba ( NO3 ) 2( aq)  K 2 SO4( aq)  BaSO 4( s )  2 KNO3( aq)
a) Which reagent is in excess? (6 marks)
b) What mass of barium sulfate would be produced? (3 marks)
7. One reaction invloved in the smelting of copper sulfide ores involves copper(I) oxide
and copper(I) sulfide:
2Cu 2 O( s )  Cu 2 S ( s )  6Cu( s )  SO2( g )
If 50.0 g of copper(I) oxide is heated with 25.8g of copper(I) sulfide
a) Determine which reagent, if any, is in excess (6 marks)
b) Calculate the theoretical yield of copper. (3 marks)
c) Determine the percentage yield if 58.0 g of copper is actually isolated. (3 marks)
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Bonus - Which is the most abundant element on the EARTH (hint – not within the universe)?