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Practice Final Exam

CHEM 110 (HOUCK)

Part I: Concepts and Simple Math Problems

1.   (6 points) Fill in the following table with the appropriate number of protons, neutrons, and electrons.

Protons         Neutrons        Electrons

52Cr2+

76 Se2- 

2.   (3 points) Give one acceptable value for each of the quantum numbers below:

the 2nd electron gained when Sulfur ionizes to S2-        n = ____  l = ____ ml = ____

3.   (5 points) What is the electron configuration (use spdf notation) ofNi2+ ?  How many valence electrons does this ion have?

4.   (10 points)

a.   Circle the atom with the largest radius                                               Ca       Ba

b.   Circle the ion with the smaller radius                                                F-              Na+

c.   Circle the atom with the higher first ionization energy                     K         Ca

d.   Circle the compound with the lowest melting point                        RbBr     NH3

e.   Circle the orbital that is the lowest in energy                                    4d        4s

5.   (6 points) In the appropriate box, provide an example of an ionic bond, polar covalent bond, and a nonpolar covalent bond.

Ionic

Polar covalent

Nonpolar covalent

 

 

 

6.    (10 points) The structure of vitamin C is shown below.

a.   What is the hybridization of atom A? _______

b.   What is the bond angle of angle B (use < or > as necessary): ________

c.   What are the orbitals that overlap to form the bond indicated by C? _____________

d.   What is the molecular formula of vitamin C?

A

C

OH

HO        

O

O

 

HO

OH

 

B

___________________

e.   Bonus: Name two functional groups in vitamin C.

7.   (4 points) Draw two constitutional isomers of the formula C3H6O2 .

8.   ( 14 points) Draw the Lewis structures of the following molecule/ion. Indicate the electron domain and molecular geometries.

Lewis structure of chlorate

 

Electron geometry:

Molecular geometry:

9.   (6 points) Provide the formal charges on the atoms in the fulminate ion below . 

 C  N  O

10. (6 points) Draw a resonance structure of the ion below .  Add lone pairs and show curved arrows to indicate the movement of electrons in the original structure .

O

O

11. Consider the following molecules:

O

O

A                                                   B                                               C

a.   (4 points) How many sigma and pi bonds are present in structure A?

σ:

_______

π:

_______

b.   (7 points) List the intermolecular forces present in each molecule.

A:

__________________________________________________

B:

__________________________________________________

C:

__________________________________________________

c.   (3 points) Which molecule will have the strongest total intermolecular forces?

_______

d.   (3 points) Which molecule will have the lowest boiling point? _______

12. (6 points) Nitrous oxides react with water to form nitric acid, a component of acid rain according to the reaction below:

3 NO2 (g) + H2O (l) à 2 NO3-(aq)  + NO (g)  +  2 H+ (aq)

a.   What is the oxidation state of N?

N in NO2 : __________               N in NO3- : ___________

b.   In the partial reaction: NO2  à NO, is NO2  acting as a reducing agent, oxidizing agent, or neither? Circle your answer.

Reducing agent                       Oxidizing agent                      Neither

13. ( 11 points) ELISA is a type of assay that can be used to detect and quantify the amount of proteins, antibodies, etc. in a sample.  Proteins can be tagged with a fluorescent marker     and the amount of light emitted is proportional to its concentration.

a.   One particular fluorescent compound will emit light of 420 nm.  What is the energy (in J/mol) and frequency (in Hz) of this light?

b.   Which of the following types of light is/are higher in energy than the light in part a?

X-ray              UV                  IR                    Microwaves                Radio waves

14. (4 points) Shown below are five curves that represent the distribution of molecular speeds of five different gases at the same temperature. The gases are H2, CH4, He, SF6, and N2 .   Which curve describes the distribution of speeds for CH4?

B.     Curve II

C.     Curve III

D.     Curve IV

E.     Curve V

15. (4 points) From the following options, which properties of an ideal gas would not      produce the relationship shown below if plotted on the X- and Y-axes? Assume other properties besides the given variables (P, V, T, or n) are constant.

 

X-Axis

Y-Axis

A

n

P

B

P

V

C

T

P

D

1/V

P

E

T

V

Part II: Longer Problems.  Show all work for full credit!

16.  Bacon  is  a  delicious treat!   Imagine you  get home  for summer break and find some frozen bacon in the freezer at - 10 oC.  You set it out on the counter to thaw.

a .   (5 points) Draw the heating curve for frozen bacon

at - 10 oC to thawed bacon at 25 oC. The freezing point of bacon is -2 oC.

25

Temp

oC

-2    

-10     

heat added

b .   (8 points) How much heat (in kJ) must be added to 1 lb (454 g) of bacon to warm it from - 10 oC to 25 oC? 

17. The whoosh bottledemo involved the combustion of ethanol in a water jug.

a.   (6 points) Write the balanced chemical equation for the combustion of ethanol (C2H6O).

b.   (8 points) 40.0 mL of liquid ethanol (d = 0.789 g/mL, MW = 46 g/mol) was burned in the presence of 15.55 g O2 . What is the limiting reagent?

_______ is the limiting reagent

c.   (6 points) If 3.72 mL of water (d = 1.00 g/mL) was isolated, what was the percent yield?

18. For the following reaction:

2 C8H18  (l) +  25 O2  (g) à 16 CO2    (g)  +  18 H2O  (g)               ΔH°rxn  =  - 5461 kJ

a .   (2 points) Is this reaction:   exothermic      or      endothermic         (circle answer)

b .   (6 points) What volume of O2  at 20 °C and 0.85 atm is required to exchange 2000 kJ of heat with the surroundings?

c .   (4 points) A container of fixed volume contains only octane and oxygen.   The reaction goes to completion with no excess reagents present.   Once the system returns to the initial temperature, is the pressure in the container after the reaction higher or lower than the initial pressure? Explain in just a few words.

d .   (6 points) What  is the partial pressure  of water  and  carbon  dioxide  after the combustion if the total pressure is 4 atm?

19. (8 points) Zinc and HCl react according to the thermochemical equation shown below.

2 HCl(aq)   +  Zn(s)     à ZnCl2 (aq)   +      H2  (g)        ΔHrxn = - 153.9 kJ

a.   0.103 g of Zn reacts with 50.0 mL (excess) of 0.1 M HCl solution initially at 22.5 °C.  What is the final temperature of the solution?  The density and specific heat of water are 1.00 g/mL and 4.184 J/g oC, respectively.

m = ___________________

20. Hydrogenation reactions are used to add hydrogen across double bonds in hydrocarbons and other organic compounds.  An example reaction is shown below:

H2C=CH2  (g)       +        H2  (g)       à  H3C-CH3  (g)

a.   (6 points) Calculate the ΔH of the reaction using bond dissociation energies. BDEs you may need (kJ/mol): C-H = 413; C=C = 620; C-C = 348; H-H = 436 

21. Methanol (CH3OH) is proposed as an alternative to fossil fuels.

a .   (4 points) Write the reaction for the formation of liquid methanol from its elements in standard states.

b .   (6 points) The combustion reaction of methanol is shown below .          Calculate the enthalpy for the reaction of 1 mol CH3OH using heats of formation and Hess’ Law . The heats of formation are as follows (all in kJ/mol): methanol = -238; carbon dioxide = -394; water = -242.

2 CH3OH(g)    +           3  O2 (g)           à  2 CO2 (g)           +    4 H2O(g) 

22. EDTA (ethylenediaminetetraacetic acid) solutions are commonly used in biological experiments.  Solutions are often prepared from the disodium salt of EDTA,

Na2(C10H16N2O8).

a.   (6 points) You need to prepare 1.5 L of a 0.50 M EDTA solution for an experiment. What is the mass of solid Na2(EDTA), MW = 372.34 g/mol required?

b.   (6 points) To the solution in part a, you also add 60.0 g of solid NaOH (MW = 40.0

g/mol) to adjust the pH.  What is the total sodium ion (Na+) concentration in the 1.5 L?

c.   (6 points) If 500 mL of the 0.5 M EDTA solution are diluted to 800 mL, what is the new EDTA concentration?