PRACTICE WORK-49: STOICHIOMETRY Limiting Reagents ...

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PW49A ? LIMITING REAGENTS Do Date Section M T W R

PRACTICE WORK-49: STOICHIOMETRY Limiting Reagents, Theoretical Yield, and Percent Yield-01

General Information Do Date: 5/2 You will need the periodic table, Notes-55

Reaction 1:

137.33 g/mol

70.90 g/mol

Ba

+

Cl2

208.23 g/mol

BaCl2

1) Student A performs Reaction 1 above. He calculates that the theoretical yield is supposed to be 18.0 grams of barium chloride. His experimental yield is 15.4 grams. Calculate the percent yield.

2A) Student B performs Reaction 1 and obtains a percent yield of 97.2%. Write this percentage as a conversion factor. (See Notes-55)

2B) If the actual yield was 42.1 grams, use the conversion factor in 2a to determine the theoretical yield.

3A) Student C performs Reaction 1 and obtains a percent yield of 87.1%. Write this percentage as a conversion factor.

3B) If the theoretical yield is 212.3 g BaCl2, use the conversion factor from 3a to determine the actual yield.

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CHEM 110 (BEAMER)

PW49A ? LIMITING REAGENTS

INFORMATION FOR QUESTIONS 4A ? 4E

molar mass 70.90 g/mol

2 Cl2

+

26.98 g/mol

133.33 g/mol

3 Al

2 AlCl3

4A) How much aluminum chloride (grams) can be obtained from 10.00 grams of chlorine gas and 10.00 grams of aluminum metal? (This is another way of asking for the theoretical yield of aluminum chloride.)

4B) What is the theoretical yield? 4C) Which substance is the limiting reagent? (LR) 4D) Which substance is the reactant in excess (XS) 4E) A student performs this experiment, and obtains 16 grams of aluminum chloride. Calculate the percent yield.

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CHEM 110 (BEAMER) INFORMATION FOR QUESTIONS 5A ? 5D

molar mass 123.88 g/mol

P4

+

2.02 g/mol

34.00 g/mol

6 H2

4 PH3

5A) How much phosphine gas will be formed from 20. grams of phosphorus (P4) and 10. grams of hydrogen?

PW49A ? LIMITING REAGENTS

5B) What is the theoretical yield? 5C) Which substance is the limiting reagent? (LR) 5D) Which substance is the reactant in excess (XS) 5E) A student performs this experiment, and obtains 15.72 grams of aluminum chloride. phosphine. Calculate the percent yield.

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CHEM 110 (BEAMER) INFORMATION FOR QUESTIONS 6A ? 6D

molar mass 256.56 g/mol

3 S8

+

50.94 g/mol

198.09 g/mol

16 V

8 V2S3

PW49A ? LIMITING REAGENTS

6A) A student performs this experiment and obtains a percent yield of 94.4%. If the experimental yield is 23.18 grams of vanadium(III) sulfide, calculate the theoretical yield of vanadium(III) sulfide. (Another way to say this is: "Calculate the mass of vanadium(III) sulfide that the student should have gotten.")

Hint: See Questions 1 through 3 on this packet. Max Time = 6 min. Max Time on Exam = 4 min

6B) Assume that we are still using the information from Question 6a. Assume that vanadium is the limiting reagent. Calculate the initial mass of vanadium.

6B) CHALLENGE PROBLEM: Assuming that we are still using the information from Question 6a. Assume that sulfur was the reactant in XS. Calculate the mass of leftover S8, assuming that the student began with 20.00 grams of sulfur. Hints: For the first part of this question, use the theoretical yield of V2S3 to determine the initial amount of sulfur used. For the second part of this question, you will need to do simple subtraction.

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CHEM 110 (BEAMER)

Answers

1)

85.6%

PW49A ? LIMITING REAGENTS

2a) 97.2 g BaCl2 expt = 100 g BaCl2 theor

2b) 43.3 g BaCl2

3a) 87.1 g BaCl2 actual = 100 g BaCl2 theor

3b) 184.9 g BaCl2

4a) 18.81 g AlCl3

4b) 18.81 g AlCl3. (Yes, this is the same answer as 4a. It's just another way of wording it.)

4c) Cl2

4d) Al

4e) 83.57%

5a) 22 g PH3

5b) 22 g PH3 (Yes, this is the same answer as 5a. It's just another way of wording it.)

5c) P4

5d) PH3

5e) 73%

6a) 24.56 g V2S3

6b) 12.63 g V

6c) 20.00 g ? 11.93 g = 8.02 g S8 leftover

A solutions set will be posted.

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