Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 109

Chem 109, Dr. Paselk

Hour Exam I
 Name
Fall 1994

(100 pts)
 Lab

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This examination is scheduled for fifty (50) minutes. At the end of this fifty minute period you will have five (5) minutes to place your examination at the front of the examination room.

Show Work for Credit!!!!!!

1. (12 points @ 2 points each). Answer the following in the spaces provided:

How many moles of NaBr are in 73 mL of a 1.500 M solution?_____________

What is the mass of 6.02 x 1020 atoms of gold? _____________

How many P4 molecules are there in 6.0 g of phosphorus? _____________

How many molecules are there in 22.4 l of N2 (g) at 273 K under 1.00 atmosphere pressure? _____________

If equal volumes of each of the gases: H2, O2, N2, CH4, Ne filled the same sized balloons and a small hole is poked in each, which balloon will deflate last? _____________

What is the % by mass of carbon in CO? _____________

 

2. (8 points @ 2 points each) Briefly answer the following:

Name the compound with the formula: WO3? _____________

What is the value for the heat of formation for oxygen (O2) _____________

What is the formula for cobalt (III) sulfate? _____________

What are the units for molarity? _____________

 

3. (8 points @ 4 points each) Complete and/or balance with integral coefficients:

 

___ NH3 + ____ O2 Æ ____ NO + ____ H2O

___ B + ____ KOH Æ ____ K3BO3 + ____ H2

4. (8 points) The density of mercury is 13.53 g per mL at 25°C. What is its molar concentration under these conditions?

 

 

 

5. (16 points) A 6.768 g sample of methanol (CH3OH) is ignited in a rigid 2.500 liter container into which 3.50 liters of oxygen at 2.017 atm and 23.0 °C has been introduced.

a. Write a balanced equation for the reaction, using integral coefficients.

 

 

b. Assuming the reaction goes to carbon dioxide and water products, calculate the number of liters of carbon dioxide produced at the above temperature and pressure.

 

 

 

6. (15 points) A compound composed of mercury, nitrogen and oxygen is analyzed and found to contain 76.39% mercury and 5.33% nitrogen.

a. Find the empirical formula for this compound.

 

 

 

b. If the compound has a formula weight of approximately 500 g, find its "molecular" formula.

 

 

c. Name this compound. (Hint: it is made up of only two types of ion)

 

7. (15 points) Butane (C4H10) is a useful aerosol propellant since it is fairly innocuous environmentally. Consider a 925 mL aerosol can containing 7.25 g of butane at 23.0 °C. What will the pressure in this can become if it is heated to 690°C in a fire, assuming the can is rigid (there is no volume change)?

 

8. (8 points) A 0.95 kg cast iron pan is heated from room temperature (20.0 °C) to 125.0 °C on a gas stove. Assuming the heat capacity of the pan remains constant cover this temperature range, calculate the quantity of heat absorbed by the pan ( heat capacity of Fe = 25.1 J °C-1mol-1).

 

 

 

 

9. (10 points)

a) What is the molarity of a solution made by dissolving 5.34 g of magnesium iodide (MgI2) in enough water to make up a volume of 500.0 mL.

 

 

 

b. How many mL of a 0.250 M solution of magnesium iodide will be needed to make up 250.0 mL of a solution which has an iodide concentration of 0.025 M?

 

 


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