**CHM 2045C Module Five Sample Exam**

**Part B: Mole calculation (Sections
2.5) 4 points**

Calculate the mass in grams of **1.16 x 10 ^{22}**
molecules of

**Answer: 5.39 g N _{2}**

**Sample Problems in Kotz6e text: p 91 Problems #27-34 **

**Optional Homework: 2.5 points paper and pencil**

**Calculate the number
of molecules in 0.641 g of oxygen gas, O_{2}**

**Answer: 1.21 x 10 ^{22} molecules O_{2}**

**Sample Problems in Kotz6e text: p 91 Problems #27-34 **

**Optional Homework: 2.5 points paper and pencil**

**Part
C: Percent Composition (section 3.6) 3 points**

Calculate the
percent composition of each element in the following compound:

**Online**: **http://people.emich.edu/bramsay1/ccc-release/chem.html**

**Answers: 6.71% Hydrogen; 40.00% Carbon; 53.28% Oxygen**

**Acetic Acid HC _{2}H_{3}O_{2}**

**Sample Problems in the Kotz6e text:
p 134 #41-46 **

**Optional Paper & Pencil:
Homework 2.5 points**

**Part
D: Empirical Formula Calculation (Section 4.6) 4 points**

Given the following
percent compositions, determine the empirical formula of the following
compound: **54.5% carbon, 9.15% hydrogen, **and** 36.3% oxygen**

**Answer: C _{2}H_{4}O_{1}**

**Sample Problems in the Kotz6e text:
p 134-135 #47-56**

**Optional Paper & Pencil:
Homework 2.5 points **