CHEM125-B                                                                                                  Fall, 2006

Hourly Exam # 2                                                                                             Dunnivant

 

Name (PRINTED) ____________________________________

 

There are 100 points, plus a five point bonus question.

 

The honor statement must be signed in order for your exam to be graded.

Closed book, closed Internet, closed notes, closed neighbor!

 

I have neither given nor received aid on this exam.  

                                                            Signature ________________________

 

AvogadroÕs number = 6.022 x 1023 items/mol           

amu = 1.6605 x 10-24 g/amu

 

NOTES:

-Show all work for partial credit.  

-Significant figures and units will be graded throughout the exam.

 

 

  1. (10 pts total; ~0.5 pts each) Complete each list below the heading:  Give the chemical formula for

 

Six strong acids     four strong bases         three weak acids          six weak bases

 

____________      _____________          ____________            ___________

 

____________      _____________          ____________            ___________

 

____________      _____________          ____________            ___________

 

____________      _____________                                              ___________

 

____________                                                                              ___________

 

____________                                                                              ___________

 

  1.  (20 pts) Given below is the name or symbol of a compound.  Fill in the table and tell if the compound will be soluble or insoluble.

 

IUPAC Name                   Chemical formula                    Soluble (S) or Insoluble (I)

 

Example:   Sodium chloride             NaCl                                       S

 

Sodium sulfide                  __________                            ___

                 

__________                      Hg2Cl2                                     ___

 

__________                      FePO4                                     ___

 

Calcium sulfate                  __________                            ___

 

Cadmium (II) phosphate   __________                            ___

 

__________                      PbO                                         ___

 

__________                      NH4MnO4                               ___

 

Strontium hydroxide         __________                            ___

 

__________                      Ca(CH3COO)2                                    ___

 

__________                      CaS                                         ___

 

 

  1. (10 pts; 0.5 pts each)  Give the oxidation state of each element in the following reactions.  When necessary complete and balance the reaction.

 

__ C4H8O2  +  __ O2    __         +  __     

 

Reactant oxidation states:              C  _____         H  _____         O _____ (in O2)

 

Products oxidations states:            C  _____         H  _____         O _____

 

__ NaN3    __ Na  +  __ N2

 

Reactant oxidation states:              Na  _____       N  _____        

 

Products oxidations states:            Na  _____       N  _____        

 

 

  1. (5 pts)  Label each reaction as acid/base, precipitation, or redox.

 

a)     type of reaction:  __________

 

Cu(OH)2(s)  +  2HNO3(aq)    Cu(NO3)2(aq)  +  2H2O(l)

 

b)    type of reaction:  __________

 

Fe2O3(s)  +  3CO(g)    2Fe(s)  +  3CO2(g)

 

c)     type of reaction:  __________

 

Sr(NO3)2(aq)  +  H2SO4(aq)    SrSO4(s)  +  2HNO3(aq)

 

d)    type of reaction:  __________

 

4Zn(s)  +  10H+(aq)  +  2NO3-(aq)    4Zn2+(aq)  +  N2O(g)  +  5H2O(l)

 

 

  1. (15 pts)  You have two solutions:  125 mL of a 0.0105 M HCl solution and 50.5 mL of a 0.290 M NaOH solution.  What is the maximum amount of NaCl and H2O that you can make, assuming the reaction goes to completion?  You will need to perform a variety of calculations to complete this problem, but summarize your answers in a complete flow chart.

 

 

6. You are asked to make 250.0 mL of a 1.567 x 10-2M solution of MgSO4-7H2O.       

 

a)  (5 pts)  How much of the salt/compound do you need to weigh out?  __________g

 

b) (5 pts)  If you take 100.0 mL of the solution described above, add it to a 500.0 mL volumetric flask, and fill it to the ÒmarkÓ, what is the new concentration of Mg2+?

 

___________________

 

 

7.     (5 pts)  The following reactions occur in every high temperature combustion process.  Given these two individual reactions

 

N2(g)  +  O2(g)    2NO(g)                                 DH = +180.7 kJ

2NO(g)  +  O2(g)    2NO2(g)                            DH = -113.1 kJ

 

                  determine the enthalpy of reaction for the overall process represented by

 

                  4NO(g)    2NO2(g)  +  N2(g)

 

                  DH = __________ kJ.

 

 

8.     (1 pt. each)

 

A negative DG value indicates that the reaction is endothermic or exothermic? (circle the correct answer)

 

True or False: A negative DG value for a given reaction means that the reaction will always be spontaneous.

 

A positive DH value indicates that the reaction is endothermic or exothermic? (circle the correct answer)

 

A negative DS value indicates that the reaction is endothermic or exothermic? (circle the correct answer)

 

In general, should DS increase or decrease in a spontaneous reaction?

 

 

 

9.     (15 pts.) The temperature of a flame, and the heat generated by a given combustion reaction, are dependent on the properties of the reactants.  Different fuels yield different flame temperatures.  It is commonly known that a H2/O2 flame is cooler than an acetylene (C2H2)/O2 flame.  Prove this using what you have learned in thermodynamics.  As a basis for your calculations, assume 1.000 mole of each fuel and express your answer per mole of each fuel.

 

 

 

10.  (5 pts.)  Logic question: A 25.5 g piece of cheese contains 37% fat, 28% protein, and 4% carbohydrate.  The respective fuel values for protein, fat, and carbohydrate are 17, 38, and 17 kJ/g.  The fuel value for this piece of cheese is ___________ kJ.

 

 

 

 

 

 

5 pts. Bonus question.  In question #5, after you mix stiochiometric equivalent volumes of the reactants, what is the molar concentration of Na+ in the final solution?