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.

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.

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