CHM 2045C Module 5 Sample Exam Answers Part I

Part I Mole-Mole Stoichiometry 4 points

1. Tungsten occurs in the important mineral sheelite (Calcium tungstate), which is converted to tungstic acid. Tungsten is then extracted from tundstic acid by the following (unbalanced) reaction:

3 H₂ + H₂WO₄ à W + 4 H₂O (balanced)

How moles of hydrogen are needed to prepare 6 moles of elemental tungsten?

Question: ____?_____moles _H2 = 6 moles _W

2. Phosphoric acid can be made by the following (unbalanced) reaction:

6 H₂O + P₄O₁₀ à 4 H₃PO₄

How many moles of Phosphoric acid can be prepared from the combination of 5 moles of Tetraphosphorus decoxide with excess water?

Question: ____?_____moles _H3PO4 = 5 moles _P4O10

Suggested Additional Homework Problems: p166 #7. Page167 #15-16

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Module 5 Sample Exam Answers Part J

Module Five-Part J Mass-Mass Stoichiometry 4 points

1. Toluene and nitric acid are used in the production of trinitrotoluene (TNT), an explosive:

C₇H₈ + 3 HNO₃ à C₇H₅N₃O₆ + 3 H₂O (balanced)

Calculate the mass of TNT that can be made from excess C₇H₈ (toluene) with 126 grams of Nitric acid.

ANSWER: 151 g TNT

Question: ____?____g C₇H₅N₃O₆ = 126 g HNO₃

Using ChemiCalc ANSWER: 151 g TNT

2. What mass of carbon dioxide is produced from the combustion of 176 grams of propane gas , C₃H₈ , in excess oxygen gas, O₂. Water is the only other product. Write and balance the equation for combustion.

ANSWER: 527 g CO₂

C₃H₈ + 5 O₂ à 3 CO₂ + 4 H₂O

Question:

_____?_____g CO₂ = 176g C₃H₈

Using ChemiCalc ANSWER: 527 g CO₂

Suggest Additional Homework Problems Kotz6e: p166-7 #8-14, 17-18