EXAMINER(S) | DR. EUODIA HESS DR. JULIEN LUSILAO …

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NAMIBIA UNIVERSITY OF SCIENCE AND TECHNOLOGY

FACULTY OF HEALTH AND APPLIED SCIENCES

DEPARTMENT OF NATURAL AND APPLIED SCIENCES

QUALIFICATION: BACHELOR OF SCIENCE

QUALIFICATION CODE: 07BOSC LEVEL: 5

COURSE NAME: GENERAL CHEMISTRY 1B COURSE CODE: GNC502S

SESSION: NOVEMBER 2019 PAPER: THEORY

DURATION: 3 HOURS MARKS: 100

FIRST OPPORTUNITY EXAMINATION QUESTION PAPER

EXAMINER(S) | DR. EUODIA HESS

DR. MARIUS MUTORWA

MODERATOR: | DR. JULIEN LUSILAO

INSTRUCTIONS

Answer ALL the questions.

Write clearly and neatly.

Number the answers clearly

All written work must be done in blue or black ink and sketches can be done in pencil

PON b

P

5. No books, notes and other additional aids are allowed

THIS QUESTION PAPER CONSISTS OF 12 PAGES (Including this front page and attachments)

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SECTION A

QUESTION 1: Multiple Choice Questions

[50]

[50] There are 25 multiple choice questions in this section. Each question carries

2 marks.

Answer ALL questions by selecting the letter of the correct answer.

Choose the best possible answer for each question, even if you think there is

another possible answer that is not given.

Which of the following is true regarding the relative molar rates of disappearance of the reactants and the appearance of the products?

2NO (g) + 2H2 (g) > No (g) + 2H20 (g)

I. Nz appears at the same rate that H2 disappears.

Il. H2O appears at the same rate that NO disappears.

lll. NO disappears at the same rate that H> disappears.

A. lonly

B. land Il only

C. land Ill only

D. Il and Ill only

E. LI, and lll

For the reaction 2A + B > C, experimental data were collected for three trials:

Experiment | [A] (M) [B] (M) Initial Rate Appearance of C (M sec?)

1 0.40 0.20 5.5x 10°

2 0.80 0.20 5.5x 10°

3 0.40 0.40 2.2 x 107

What is the rate law of the reaction?

A. Rate = k[A][B]

B. Rate = k[A]°[B]?

C. Rate = k[A]2[B]?

D. Rate = k[A]?[B]°

E. Rate = k[A][B]?

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3. For areaction A + B > C+D, the energy of activation and enthalpy change of reaction were found to be 80 kJ mol and + 20 kJ mol, respectively. What is the value of the activation energy for the reverse reaction?

A. + 60 kJ mol?

B. + 100 kJ mol?

C.—80 kJ mol

D. + 20 kJ mol

E. Insufficient information

4. Write the appropriate equilibrium constant expression, Kc, for the following reaction:

2CO(g) + O2(g) 2CO2(g)

A. Ke =k[CO]*[O2]

[co, ] PKs = Feofo,]

[coP [o,] “Teo, |

_ {co,f *~ |cofo,]

__[co,P [coP’[o, ]

c

5. Suppose we rewrite the balanced reaction in Question 4 as:

CO(g) + % O2(g) CO2(g)

What would be the equilibrium constant, K, for this reaction?

A. Same(i.e. Ke” = Ke)

B. Ke’ = (Ke)”

C. Ke =K-/2

D. Ke’ = Ke2

E. Ke =1/K

6. If Keq is small, it indicates that equilibrium occurs:

At a low product concentration

At a high product concentration

After considerable time

With the help of a catalyst

mo

fo 8S >

With no forward reaction

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Vs

10.

For which one of the following equilibrium equations will Kp be equal to K.?

A. PCls(g) S PCl3(g) + Cla(g)

B. COCl2(g) S CO(g) + Clo(g)

C. H2(g) + la(g) S 2HI(g)

D. 3H2(g) + No(g) S 2NHa(g)

E. 2S03(g) 2SO2(g) + O(g)

Consider the following equilibrium:

H2(g) + lo(g) S 2HI(g)

At equilibrium [H2] = 0.00220 M, [lz] = 0.00220 M, and [HI] = 0.0156 M. The value of the Ke is

A. 3.10 x 10%

B. 1.99 x10?

C. 5.03 x 10!

D. 3.22 x 10°

E. 1

Arrhenius would define a base as:

I. Something which yields hydroxide ions in solution

ll. A proton acceptor

Ill. An electron pair donor

A. 1, Il, and Ill

B. land Ill

C. Ilonly

D. lonly

E. land Ill

In the equilibrium expression for the reaction BaSOa(s) Ba?*(aq) + SO7 (aq), Ksp is equal

to:

[Ba** ][SO77]

, [Baso, |

B. [BaSO, ]

[Ba** ][SO7]

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C. [Ba**][SO7

[Ba** [SOF] BaSO,

E. None of the above

11. Calculate the concentration (mol/L) of a solution of Ba(OH)2 that has a pH of 12.7?

12.

13.

A. 1.0x 1073

B. 5.0x 10?

C. 2.0x10¥

D. 2.5x 10?

E. 1.27x10!

A buffer solution was prepared by mixing 100 mL of a 1.2 M NH3 solution and 400 mL of a 0.5

M NH4CI solution. What is the pH of this buffer solution, assuming a final volume of 500 mL

and Kp= 1.8 x 10°?

What kind of hybridization do you expect for each of the carbon atoms indicated in 2- methylpropene?

— 24g |

p>

O

Q-O

Ais sp?; Bis sp; Cis sp

Ais sp?; B is sp?; Cis sp?

A is sp’; B is sp; Cis sp?

9 9 F >

Ais sp; B is sp?, Cis sp?

E. Ais sp?; Bis sp; Cis sp?

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14. The structure below is that of Capsaicin, the pungent substance in chilli peppers.

O

2 N ao | H

HO

The functional groups of the above structure include:

amide; ester; alcohol; alkene

ether; amide, alkyne; alcohol

alcohol; ester; ether; amine

ester; carboxylic acid; alkene; alcohol

mofo

f >

amine; ester; alkene; alcohol

15. What is the correct IUPAC name for the compound shown below?

3-methyl-4-(1-methylethyl)-5-(propyl)-6-(dimethyl) octane

4-isopropyl-3-methyl-tert-pentylnonane

4-(1, 1-dimethylpropyl)-5-(1-methylethyl)-6-(methyl) nonane

3-methyl-4-(1-methylethyl)-5-(1,1-dimethylpropyl) nonane

mono

8 >

3-methyl-4-(1,1-dimethyl)-5-(1,1-dimethylpropyl) nonane

16. The line-bond structure shown below is the compound Folic Acid, an essential vitamin that the body uses to make DNA and metabolise amino acids.

HoN N N

N Zz NH a N O

OH NH OH

Zz O OH

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The correct molecular (or condensed) formula for Folic Acid is:

A. CigHi9N7Oq

B. Ci9H7N7O¢

C. CisHi3N7Oc¢

D. CigHigN7O¢

E. C1i9H33N70¢

17. Which one of the structures in a to d is NOT a valid resonance structure for the anion in the

box below?

O:

EH 3

O: : :O:

a. Hie Kon, b. Hoo SoH, c. Hee by d. yc cH 3 3

moO WB >

oo

noaoa»o

w

18. How are the molecules in the following pair related?

i -OH and

H3C~ ~CHg HS NH

They are constitutional isomers

They are stereoisomers

They are resonance structures

Conformational isomers

moo

7 >

They are unrelated

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19. Which of the following molecules contain both covalent and ionic bonds?

CH30H NaoCO3 NHyCl NaCl I Il Il IV

A. land Il

B. land IV

C. I, land Iv

D. Iland Ill

E. Il, land IV

20. Which of the molecules below are polar?

O I

EpC=CH, Cw H CHCbh H3;C—CH3; CH;0H

I I II IV Vv

A. Ill, Vand V

B. land IV

C. Il, land V

D. land Ill

E. 1, ll, land V

21. What is the electron configuration for the Fe3+ ion?

A. [Ar]4s13d6

B. [Ar]4s93q7

C. [Ar]4s03d5

D. [Ar]4s23d9

E. [Ne]3s23p10

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22. Using the VSEPR model, the molecular geometry of the central atom in tetrafluoroborate

22%

24.

25.

ion is

A. trigonal planar

B. square pyramidal

C. square planar

D. trigonal bipyramidal

E. octahedral

The electron domain and molecular geometry of BrO?- is

A. tetrahedral and trigonal planar

B. tetrahedral and bent

C. trigonal planar and trigonal planar

D. trigonal pyramidal and linear

E. trigonal pyramidal and seesaw

The hybridizations of bromine in BrFs and of arsenic in AsFs are and

, respectively.

A. sp3d2, sp3d

B. sp3, sp3d

C. sp3d, sp2d2

D. sp3d, sp3

E. sp3d2, sp>d2

A valid Lewis structure of

A. POa>

B. SeF4

C. CF4

D. SiFa

E. NF3

cannot be drawn without violating the octet rule.

END OF SECTION A

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SECTION B: [50]

QUESTION 1 [3]

Considering the following reaction: 2SO3 (g) 2SQz (g) + O2 (g) AH® = +197 kJ What will happen to the number of moles (increase, decrease or remain the same) of SO3 in equilibrium with SO2 and Oz in each of the following cases?

a. Oxygen gas is added. (2)

b. The pressure is increased by decreasing the volume of the reaction container. (2)

c. The temperature is decreased. (2)

d. Gaseous sulphur dioxide is removed. (2)

QUESTION 2 [10]

2.1 In a NaOH solution, [OH] is 2.9 x 10 M. Calculate the pH of the solution. (2)

2.2 Calculate the pH of a:

a. 1.0 x 10° M HCl solution (4)

b. 0.020 M Ba(OH)2 solution (4)

QUESTION 3 [7] 3.1 Balance the following half reactions:

a. CrO4~ (aq) > Cr(OH)s(s) (in basic medium) (3)

b. HNO2 (aq) > NH@ (aq) (in acidic medium) (3)

3.2 Find the oxidation number of Cr in K2Cr207 (1)

QUESTION 4 [12]

A molecular compound is composed of 60.4% Xe, 22.1% O and 17.5% F, by mass. If the molecular weight is 217.3 amu:

4.1 What is the molecular formula? (5)

4.2 Draw the most dominant Lewis structure of the compound? (3)

4.3 Predict the molecular geometry using VSEPR model. (2)

4.4 Describe the bonding using valence bond theory. (2)

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QUESTION 5

5.1 Arrange the bonds in each of the following sets in order of increasing bond polarity.

a. C-F; O-F and Be-F

b. O-Cl; S-Br and C-P

5.2 Draw all possible resonance structures of the following molecules.

a. SeQ2

b. C204

QUESTION 6

6.1 The molecule AsF3 has a dipole moment of 2.59D. Which of the geometries are possible: trigonal planar, trigonal pyramidal or T-Shaped? Explain your choice of answer.

6.2 What is the formal charge of the central atom in the SiF,2" ion?

THE END

GOODLUCK

[8]

(4)

(4)

[5]

(3)

(2)

USEFUL CONSTANTS:

Gas constant, R = 8.3145 J-mol?: kK? = 0.083145 dm?: bar: mol: K2

= 0.08206 L atm mol?: K2

1Pa:m?=1kPa.l =1N-m =1)J

1 atm = 101 325 Pa = 760 mmHg = 760 torr

Avogadro’s Number, Na = 6.022 x 1023 mol?

Planck’s constant, h = 6.626 x 1034 Js

Speed of light, c = 2.998 x 108 ms?

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