Chem 121                                Sample Exam #1

ALL WORK MUST BE SHOWN WHERE APPROPRIATE.  Proper handling of significant digits is assumed in all mathematical problems.  Suggested time limit = 1 hour

1.         Some hydrochloric acid is spilled on the lab floor. Sodium hydrogen carbonate is sprinkled on the spill to neutralize the acid. The balanced equation for the reaction that takes place is

 NaHCO₃           +     HCl ®         NaCl    +       CO₂       +         H₂O

   If 100.0 ml of 3.00 M HCl was spilled, what is the minimum amount (in grams) of NaHCO₃ that must be sprinkled to neutralize all the acid in the spill?

2.         Decide whether a precipitate will form when silver nitrate and lithium carbonate solutions are mixed. If a precipitate forms, write a net ionic equation for the reaction.

3. If 3.50 gram of C₁₂H₂₂O₁₁ is dissolved in enough water to give 650 mL of solution, what is the molarity of the solution?

4. Describe how you would prepare 300 mL of 0.100 M (NH₄)₂SO₄ starting with a 2.50 M stock solution.

5. From the following heats of reaction:

N₂(g)+2 O₂(g)®2 NO₂(g)DH = +67.6 kJ

2 NO(g)+ O₂(g)®2 NO₂(g)DH = -113.2 kJ

calculate the heat of the reaction

 
 

6.   Using data found in the thermodynamic tables in the appendix of your text, calculate the standard enthalpy change for the reaction:

NH₃(g)+HCl(g)®NH₄Cl(s)
 
 

7. a. Write a total ionic equation for the following and identify the spectator ions:

HC₂H₃O₂(aq)+KOH (aq)®KCl(aq)+H₂O(l)

b. Write a net ionic equation for the reaction in a. above.

8.            (10 pts) Determine the oxidation number of the underlined atom in each of the following:

a.  H₂CrO₄

b.PO₃^-

c.ClO₂^-

9.          (10 pts) Which of the two reactions below is oxidation/reduction?

        3Ca(OH)₂   +     2 H₃PO₄®          Ca₃(PO₄)₂         +       6 H₂O

                        Cu   + 2 HNO₃®       Cu(NO₃)₂       +     2 H₂O

For the redox reaction, indicate the species oxidized, the species reduced, the reducing agent and the oxidizing agent.
 
 

10. A 3.0 L sample of gas at 1.0 atm and 0.0°C is heated to 85°C. Calculate the gas volume at the higher temperature if the pressure remains at 1.0 atm.

11. An experimental chamber has a volume of 60 L. How many moles of oxygen gas will be required to fill the chamber at STP?

12. A 250 mL sample of oxygen gas is collected by water displacement. As a result, the oxygen is saturated with water vapor. The partial pressure of the water vapor at the prevailing temperature is 22 mm Hg. Calculate the partial pressure of the oxygen if the total pressure of the sample is 720 mm Hg.