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 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 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




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 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.

ANSWER: 527 g CO2


C3H8 + 5 O2 3 CO2 + 4 H2O


_____?_____g CO2 = 176g C3H8



Using ChemiCalc ANSWER: 527 g CO2


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