GENERAL CHEMISTRY I
CHEM 1311.002
EXAM 3
Thursday November 12, 1998

Name__________________________________________

SSN___________________________________________

1. When aqueous solutions of potassium carbonate (K2CO3) and calcium chloride (CaCl2) are mixed, a reaction occurs, producing a precipitate as one of the products. The molecular form of the equation for this reaction is

     K2CO3(aq)      +      CaCl2(aq)      ---------->      CaCO3(s)      +      2KCl(aq)

Which ions (if any) are spectator ions in this reaction? Hint: Work out the ionic and (if possible) net ionic equations for this reaction to help you answer this question.

     a) K+ and Ca2+      b) Ca2+ and Cl-      c) K+ and CO32-      d) K+ and Cl-

     e) There are no spectator ions in this reaction

2. Is there a net ionic equation for the reaction in problem 1, and if so, what is it?

     a) There is no net ionic equation for this reaction

     b) K+(aq)      +      Cl-(aq)      ---------->      KCl(aq)

     c) Ca2+(aq)      +      CO32-(aq)      ---------->      CaCO3(s)

     d) 2K+(aq)      +      Ca2+(aq)            +      CO32-(aq)      +      2Cl-(aq)      ---------->

               CaCO3(s)      +      2KCl(aq)

3. A chemistry student was wondering what would happen if aqueous solutions of ammonium chloride (NH4Cl) and potassium nitrate (KNO3) were mixed. The student wrote the following proposed reaction (in molecular form):

     NH4Cl(aq)      +      KNO3(aq)      ---------->      NH4NO3(aq)      +      KCl(aq)

In working out the ionic and (if possible) net ionic equations, which ions (if any) should be regarded as spectator ions?

     a) NH4+ and NO3-      b) K+ and Cl-      c) NH4+, K+, NO3- and Cl-

d) There are no spectator ions in this reaction

4. Is there a net ionic equation for the reaction in problem 3, and if so, what is it?

     a) There is no net ionic equation for this reaction

     b) NH4+(aq)      +      NO3-(aq)      ---------->      NH4NO3(aq)

     c) K+(aq)      +      Cl-(aq)      ---------->      KCl(aq)

     d) NH4+(aq)      +      K+(aq)      +      NO3-(aq)      +      Cl-(aq)      ---------->

               NH4NO3(aq)      +      KCl(aq)

5. Hydrobromic acid (HBr) is a strong acid and ammonia (NH3) is a weak base. The equation for the neutralization of HBr with NH3, written in molecular form, is

     HBr(aq)      +      NH3(aq)      ---------->      NH4Br(aq)

Which ions (if any) are spectator ions in this neutralization reaction?

     a) H+      b) Br-      c) H+ and Br-

     d) There are no spectator ions in this neutralization

6. Nitrous acid (HNO2) is a weak acid and sodium hydroxide (NaOH) is a strong base. The equation for the neutralization of HNO2 with NaOH, written in molecular form is

     HNO2(aq)      +      NaOH(aq)      ---------->      NaNO2(aq)      +      HOH(l)

Which ions, (if any) are spectator ions in this neutralization reaction?

     a) Na+      b) OH-      c) Na+ and NO2-      d) Na+, H+, OH- and NO2-

     e) There are no spectator ions in this neutralization

7. Ions that can be cancelled out of the ionic equation

     a) are spectator ions      b) are not spectator ions

8. If there are no spectator ions in an ionic equation, then

     a) there will be no net ionic equation

     b) the net ionic equation will be exactly the same as the ionic equation

9. Acid / Base neutralization reactions in which the base is strong belong to the __________class of reactions.

     a) combustion      b) combination      c) decomposition

     d) displacement      e) metathesis

10. Acid / Base neutralization reactions in which the base is weak belong to the __________class of reactions.

     a) combustion      b) combination      c) decomposition

     d) displacement      e) metathesis

11. When writing the ionic equation for an Acid / Base neutralization reaction, you __________strong acids.

     a) split      b) do not split

12. When writing the ionic equation for an Acid / Base neutralization reaction, you __________strong bases.

     a) split      b) do not split

13. When writing the ionic equation for an Acid / Base neutralization reaction, you __________weak acids.

     a) split      b) do not split

14. When writing the ionic equation for an Acid / Base neutralization reaction you __________weak bases.

     a) split      b) do not split

15. When writing ionic equations, you __________ water soluble ionic compounds.

     a) split      b) do not split

16. When writing ionic equations, you __________ water insoluble ionic compounds.

     a) split      b) do not split

17. When water appears as a product in a molecular equation for which you are writing the corresponding ionic equation, you __________ the water.

     a) split      b) do not split

18. What is the percent by mass of oxygen in potassium carbonate, K2CO3? Atomic weights needed for this problem are: K = 39.0983      C = 12.011       and      O = 15.9994.

     a) 11.58%      b) 23.84%      c) 34.73%      d) 50.00%      e) 79.98%

19. A compound known to contain only the elements nitrogen and oxygen was found to contain 30.45% nitrogen by mass. What is the empirical formula of this compound? Atomic weights need for this problem are: N = 14.00674      and       O = 15.9994.

     a) NO      b) N2O      c) NO2      d) N2O3      e) N2O5

20. A chemist was studying a compound known to contain only the elements carbon and hydrogen. Laboratory experiments with this compound revealed that it was 79.89% carbon by mass. Additional experiments showed that its molar mass was 30.07 g / mol. What is the true molecular formula (not empirical formula, unless the molecular and empirical formulas happen to be the same) of this compound? Atomic weights need to work this problem are: C = 12.011       H = 1.00794

     a) CH      b) C2H2      c) C6H6      d) CH3      e) C2H6

21. The elements nitrogen (N2) and hydrogen (H2) react to form ammonia (NH3). The balanced equation is

     N2(g)      +      3H2(g)      ---------->      2NH3(g)

If a chemist started with 8.191 g N2 and 1.038 g H2 in a closed container (with no NH3 initially persent) what is the maximum mass (that is, theoretical yield) of NH3 that could be produced inside the container? Atomic weights needed to work this problem are: N = 14.00674       H = 1.00794

     a) 2.923 g      b) 5.846 g      c) 9.229 g      d) 9.959 g      e) 15.805 g

22. Which reactant (if either) did you find was the limiting reactant while working out your answer to problem 21?

     a) N2      b) H2      c) neither -- it was a stoichiometric mixture

23. Assuming that the maximum possible amount of NH3 was produced in the reaction of problem 21, how much N2 was used in the reaction?

     a) 1.603 g      b) 2.404 g      c) 4.808 g      d) 7.153 g      e) 8.191 g

24. Assuming the maximum possible amount of NH3 was produced in the reaction of problem 21, how much H2 was left over (not used in the reaction)?

     a) 0.000 g      b) 0.213 g      c) 0.496 g      d) 0.771 g      e) 1.000 g

25. If a chemist recovered 1.507 g NH3 from the reaction in problem 21, what was the percent yield of the reaction?

     a) 51.55 %      b) 25.78%      c) 16.33%      d) 15.13%      e) 9.53%

***     END     OF     TEST     ***


ANSWERS:

1 d      2 c      3 c      4 a      5 b     

6 a      7 a      8 b      9 e      10 b     

11 a      12 a      13 b      14 b      15 a     

16 b      17 b      18 c      19 c      20 e     

21 b      22 b      23 c      24 a      25 b