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CHEMISTRY DEPARTMENTUNIVERSITY OF BOTSWANA

CHE 102 GENERAL CHEMISTRY II FINAL EXAMINATIONAPRIL 2003. TIME ALLOWED: 2 hours

Name of the student: ---

ill #: .Group and Serial Number: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

WRITE ALL ANSWERS ON THIS QUESTION PAPER.

The paper has two parts. For Section A (multiple-choice questions), circle the letterfor the correct answer for each question.For questions in Section B, use the space provided to write your answers. If youneed additional space, write on the back of the printed pages.

You may detach the Periodic Table, but you may NOT write anything on it during

IMPORTANT: It is the student's responsibility to report if any page ismissing in this paper. The paper has 10 pages in addition to the

Periodic Table.

Specific heat capacity of H2O (1) = 4.184 J/(OC.g)

Kw= 1.0 x 10-14 at 25 °C

Avogadro constant = 6.022 x 1023 mol-l

R = 8.314 J. K-1. mol-l = 0.08206 L. atm. K-1. mol-l

1 atm = 760 mm Hg.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Do not write in this table.

Total3 42MC 1

the examination.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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SECTION A (60%)

1 How many grams of water can be heated from 20.0 °C to 25.0 °C by the additionof324 J of heat?

a. 15.5b. 20.9c. 1.3 x 103d. 6.78 X 103e. 387

2.

For the reaction:C2~ (g) + Hig) -7 C2H6 (g), AHo = -137.0 kJ.

Also given, that the standard enthalpy of formation, AHof, for C2~ = 52.3

kJ/mol. What is the value of AHof (in kJ/mol) for C2H6 (g)?

a. 189.3b. -84.7c. -189.3d.84.7e. More information is needed.

3. How many moles ofK+ are present in 343 mL ora 1.27 M solution ofK3PO4?

a. 0.436b. 1.31c. 0.145d. 3.70e. 11.1

4. What is the freezing point (OC) of a solution prepared by dissolving 11.3 g ofCa(NO3)2 (formula weight = 164 gimol) in 115 g of water? The molal freezing

point depression constant for water, kf, is 1.86 °C.kg.mol-l.

a. 0.00b. 1.11c. -3.34d. 3.34e. -1.11

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5. Calculate the molality of urea (MM = 60.0 g/mol) in a solution prepared bydissolving 16 g of urea in 39 g water.

a. 96b. 0.68c. 6.8d. 0.41e. 0.15

The vapour pressure of pure water at 25 °C is 23.8 Torr. What is the vapourpressure (Torr) of water above a solution prepared by dissolving 18 g of glucose(a non-electrolyte, MM = 180 gimol) in 95 g of water?

6.

a. 24.3b. 23.3c. 0.451d. 0.443e. 23.8

7.

Nitrosyl bromide decomposes according to the following equation:

2NDBr (g) ~ 2ND (g) + Br2 (g)

A sample ofNOBr (0.64 mol) was placed in a 1.00 L flask containing no NO orBrz. At equilibrium the flask contained 0.46 mol ofNOBr. How many moles ofNO and Brz, respectively, are in the flask at equilibrium?

a. 0.18,0.18b. 0.46, 0.23c. 0.18,0.090d. 0.18,0.360e. 0.46, 0.46

8. For the reaction:4CuO (s) + C~ (g) ~ CO2 (g) + 4Cu (s) + 2H20(g)the expression for Kc is .

a. [C~] / {[CO2] [H2r}

b. [CO2] [CU] [H20r/{[CUO]4 [C~]}

c. [H20r [CO2] / [C~]

d. [CO2] [H2O] / {[C~] [CuO]

e. [C~] /{[H20r [CO2]}

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9. Which of the following will act as a weak base in water?

a. OH-b. CI-c. NO3-d. F-e. None of these will act as a weak base in water.

10. For MgF2, Ksp = 6.4xl0-9at 25 °C. Calculate the molar solubility of MgF2 in

water at 25 °C.

a. 1.2 x 10-3 mol/L.b. 1.9 x 10-3 mol/Lc. 5.7 x 10-5 mol/Ld. 8.0 X 10-5 mol/Le. 6.4 x10-9mol/L

The following infomlation is given for the reaction:A+B~P

11

Conc. of BMol/L

Initial Ratemol/CL.s)

Conc. of AMol/L

ExperimentNumber

0.7631.5260.763

2.832.8325.47

0.2730.2730.819

23

The order of the reaction with respect to the reactant A is

a.b.c.d.e.

12. For a first order reaction, a plot of is linear.versus

a. In [A1, lit

b. In [A]t,t

c. 1/[A], t

d. [A], t

e. t, 1/[A]

12340

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13. The half-life ofa first order reaction is 225 s.-1s .

The rate constant of the reaction is

a. 0.693b. 1.25c. 12.5d. 4.44 x 10-3e. 3.08 x 10-3

Determine the pH of a 0.35 M aqueous solution of CH3NH2 (methylamine).The Kb of methylamine is 4.4 x 10-4.

14.

a. 10.19b. 3.81c. 12.09d. 1.91e. 12.55

A reaction was found to be zero order in A. Increasing the concentration of Aby a factor of 3 will cause the reaction rate to .

15.

a. remain constantb. increase by a factor of 27c. increase by a factor of 9.d. triplee. decrease by a factor of cube root of 3.

16. Identify the functional group(s) in the compound shown below as

a. an amideb. amide and ketonec. amine and ketoned. aldehyde and aminee. amine and ether

Page 6 of 10

17. The major product obtained in the following reaction would be

'-/""l':;:::;~" H C I

a. 3-cWoro-3-methylhexaneb. 2-cWoro-3-methylhexanec. 2-cWoro-2-methylhexaned. 2-chloro-3-methylhexenee. 3-chloro-3-methylhexene

18. How many mono chlorination products would be possible in the reaction of thefollowing branched alkane with chlorine in the presence of light?

~a.b.c.d.e.

hybridized carbons.19. The compound shown below has-

La. only Sp3b. Sp2 and s~3c. sp and spd. sp, Sp2 and Sp3e. sp and Sp2

20. The following reaction would lead to the formation of

1. H2SO4

2-butyne

a. butanalb. 2-butenec. n-butaned. butanole. 2-butanone

23456

Page 7 of 10

SECTION B (40%)

Question 1

(3 marks)a. Write the IUP AC name of the following structures

",/~,X5- ~~~OC2Hs

o-W-NH20

b. Draw the structural formulas of 4-methylcyclohexanol and 4-methyl-2-heptene.

(3 marks)

c. The reaction of 2-methylpropane with chlorine in the presence of light may give two

products, 2-chloro-2-methylpropane and l-chloro-2-methylpropane. Taking anyoneof these products as an example, show all the steps (mechanism) of this reaction.

(4 marks)

~ClC12

YCIy +

major

Page 8 of 10

Question 2A solution is 0.150 M HNO2 (aq) and 0.100 MNaNO2 (aq).[Ka = 4.3 x 10-4 for HNO2]

(a) Write the equilibrium that exists in this solution. Give the concentration ofeach species. [2 marks]

(b) Calculate [H3O+] and pH of this solution.[4 marks]

(c) Discuss (without performing any calculations) why the pH of this solutiondoes not change if a small amount of (i) an acid or (ii) a base is added to it.

[4 marks]

(d) A particular buffer has an organic amine dissolved in water as one of itscomponents. What could be a possible other component? [1 mark]

Page 9 of 10

Question 3

(a) In a study of the equilibrium:Nig) + 3Hig) -* 2NH3(g)

0.500 mol/L N2 and 0.800 mol/L H2 were mixed and allowed to reach equilibriumin a constant volume vessel at a certain temperature, T 1. At equilibrium, themolar concentration ofNH3 was found to be 0.150 mol/L.Calculate Kc for the reaction at T 1.

[6 marks]

(b) At another temperature, T 2, it was found that Kc = 62. Calculate Kp for the

reaction at T 2. [2 marks]

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Page 10 of 10

Question 4

The reaction:2N2O (g) ~ 2N2 (g) + 02 (g)

follows the following rate law:Rate = k [N20]. At 780 DC, the rate constant, k = 3.4 s.

(i) Calculate the time required for the concentration ofN20 to decrease from aninitial value of 0.0600 mol/L to 0.0450 mol/L at 780°C.

[6 marks]

What is the half-life of this reaction at 780 °C?

[3 marks]

Would you expect the half life at 500 °C to be greater than, less than or thesame as it is at 780 °C? Explain very briefly.

[2 marks]