Student’s ID No _________________________________
UNIVERSITY OF BOTSWANA
DEPARTMENT OF CHEMISTRY
CHE101 (General Chemistry I) Semester 2 Test 2
Thursday 26 April 2018
Time allowed: 2 hours
___________________________________________________________________________
Surname: ____________________________ Other Names: __________________________
I.D. No.:______________________________
WRITE ALL ANSWERS ON THIS QUESTION PAPER!
This paper has two parts:
•
For section A (20 multiple choice questions), circle the letter for the correct answer to
each question.
•
For the 4 questions in section B, use the space provided to write your answers.
You may detach the Periodic Table, but you may NOT write anything on it during the
examination.
IMPORTANT: It is the student’s responsibility to report if any page is missing in this
paper. The paper has 11 pages including the cover page and Periodic
Table. Use Atomic weights correct to 4 significant figures.
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Useful data: NA = 6.022 x 1023 mol-1; c = 3.0 x 108 m s-1; 1.00 atm = 760 Torr; 1 m = 109 nm
Gas constant R = 0.08206 L.atm.K-1mol-1 OR 62.364 L.Torr.K-1mol-1 R = 3.29 x 1015 s-1;
Planck’s constant h = 6.63 x 10-34 J s; = 6.63 x 10-34 kg m2 s-1; RH = 1.097 x 107 m-1
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Do NOT write in this table!
MC
1
2
3
4
Total
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Student’s ID No _________________________________
SECTION A: 20 Multiple Choice Questions (20 × 3 marks = 60 marks)
Circle the letter for the correct answer to each question
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Q1.
Classify aqueous solutions of H2SO3 , CoSO4 and C12H22O11 as non, strong or weak
electrolyte, respectively.
A. Strong, weak and non electrolyte
B. Weak, non and strong electrolyte
C. Non, strong and weak electrolyte
D. Weak, strong and non electrolyte
Q2.
Which one of the following is a strong acid?
A. HNO2(aq)
B. HBr(aq)
C. HF(aq)
D. CH3COOH(aq)
Q3.
Calculate the oxidation number of As in As4 and P in Na2H3P3O8.
A. 0 and - 2.6
B. +1 and – 3.7
C. + 4 and + 3.7
D. 0 and + 3.7
Q4.
Use the half reaction method to balance the following half reaction in basic medium and
indicate which one of the following statement is TRUE?
Br – (aq)  BrO3- (aq)
A. There are 6 OH-(aq) ions on the left hand side.
B. There are 7e on the right hand side.
C. There are 2 BrO3- (aq) ions on the right hand side.
D. There are 6e on the left hand side.
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Student’s ID No _________________________________
Q5.
Calculate the molarity of a solution made by dissolving 0.750g of Na2SO4 (molar mass =
142.04 g / mol) in enough water to form exactly 850 ml of solution.
A. 6.21 x 10-2 M
B. 6.21 x 10-3 M
C. 0.621 x 10-3 M
D. 3.81 x 10-6 M
Q6.
A sample of nitrogen gas was kept in a 3.00 L container at a temperature of 35.0oC and
746 Torr pressure. Calculate the final pressure (in atm) of the gas if the temperature and
volume are reduced to 15.0oC and 1.41 L respectively.
A. 1.95 atm
B. 2.23 atm
C. 0.544 atm
D. 2.09 atm
Q7.
The molar mass of a gas is 130 g mol-1. Calculate the density of this gas at 22oC
and 743 Torr pressure.
A. 2.63 g L-1
B. 1.52 g L-1
C. 5.25 g L-1
D. 3.25 g L-1
Q8.
An unidentified gas has a measured effusion rate of 48.30 mL s-1. An equal volume of
Ar(g) (molar mass 39.95 g mol-1) has an effusion rate of 66.6 mL s-1 under the same
conditions. Find the molar mass of the unidentified gas.
A. 89.2 g mol-1
B. 76.0 g mol-1
C. 99.2 g mol-1
D. 38.1 g mol-1
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Student’s ID No _________________________________
Q9.
Calculate the total pressure (in atm) in a 4.00 L cylinder containing a mixture of 0.350
mol He(g), 0.500 mol Ne(g) and 0.250 mol Ar(g) at 25oC.
A. 6.73 atm
B. 1.21 atm
C. 8.89 atm
D. 4.40 atm
Q10.
A source of light with a wavelength of 410 nm emits a total energy of 35 Joules.
Calculate the number of photons emitted by the source.
A. 4.85 x 10-19
B. 7.21 x 1019
C. 4.85 x 1019
D. 7.21 x 10-19
Q11.
Calculate the wavelength,  (nm), for the third line in the Lyman series of the hydrogen
emission spectrum.
A. 103
B. 221
C. 76.3
D. 97.0
Q12.
Calculate de Brogile wave length for an electron (mass = 9.11 x 10-31 kg) moving at a
velocity of 5.00 x 106 ms-1.
A. 146 nm
B. 14.6 nm
C. 0.146 nm
D. 1.46 x 10-6 nm
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Student’s ID No _________________________________
Q13.
Find the number of subshells and the maximum number of electrons respectively for the
shell defined by n = 5.
A. 3 and 8
B. 5 and 50
C. 4 and 32
D. 5 and 30
Q14.
Which set of quantum numbers is allowed for an electron in an atom?
A. n = 3, ℓ = -2, mℓ = −2, ms = + ½
B. n = 3, ℓ = 0, mℓ = 0, ms = − ½
C. n = 2, ℓ = 1, mℓ = 2, ms = − ½
D. n = 3, ℓ = 2, mℓ = 0, ms = +1
Q15.
Which electronic configuration would represent an excited state?
A. 1s22s22p63s23p4
B. 1s22s22p63s2
C. 1s22s22p63s23p63d1
D. 1s22s22p3
Q16.
Sodium superoxide reacts with carbon dioxide gas and produce oxygen gas according to
the balanced equation
4NaO2(s) + 2CO2(g)  2Na2CO3(s) + 3O2(g)
Calculate the number of moles of NaO2(s) needed to completely react with 50 L of
CO2(g) at 25oC temperature and 1.00 atm pressure.
A. 6.21 moles
B. 3.06 moles
C. 1.02 moles
D. 4.09 moles
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Student’s ID No _________________________________
Q17. Compare light with a wavelength of 450 nm and light with a wavelength of 750 nm. The
light with the lower wavelength has
A.
a lower frequency.
B.
a higher frequency.
C.
the same frequency.
D.
a lower speed.
Q18. The number of orbitals and number of sub-shells in a shell with principle quantum number
4 are, respectively
Q19.
A.
4 and 8
B.
16 and 3
C.
16 and 4
D
8 and 16
What are the respective concentrations (M) of Na+ and SO42- ions produced by dissolving
35.53 g Na2SO4 in 50.00 mL of water and diluting to 1.33 L? [ MM(Na2SO4) = 142.04
g/mol ]
A. 0.188 and 0.376
B. 5.00 and 2.50
C. 1.33 and 0.665
D. 0.376 and 0.188
Q20.
An unidentified gas has a measured effusion rate of 38.4 mL.hr-1. An equal volume of
Ne(g) ( molar mass = 20.18 g.mol-1) has a rate of 56.7 mL.hr-1 under identical conditions.
Which one of the molecules could be the unidentified gas?
A. CH4
B. C3H8
C. C5H12
D. C4H8
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Student’s ID No _________________________________
SECTION B (40%)
Answer each question in the space provided. Show your WORK and REASONING in each
question; answers without logical calculations will NOT be given credit. In your
calculations, give the final answer to the correct number of significant figures.
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Question 1
a) A sample of neon gas effuses through a porous plug in 135 s. Calculate the time required
to effuse the same number of moles of CO2 gas.
[3 marks]
b) State Boyle’s Law and Sketch a plot representing the law.
[2 marks]
c) A quantity of N2 gas originally held at 4.75 atm pressure in a 1.00 L container at 26oC is
transferred to a 10.0 L container at 20oC. A quantity of O2 gas originally at 5.25 atm and
26oC in a 5.00 L container is transferred to this same container. What is the total pressure
in the new container?
[4 marks]
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Student’s ID No _________________________________
Question 2
a) An aqueous solution AlCl3 has a concentration of 0.150M. What volume of this solution
will contain 2.50 x 10-2 moles of Cl-.
[3 marks]
b) Use the half-reaction method to balance the following redox reaction in basic medium
clearly indicating which half-reaction is the oxidation and which is the reduction step:
SO32-(aq) + MnO4-(aq) → SO42-(aq) + MnO2(s)
[7 marks]
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Student’s ID No _________________________________
Question 3
a) Using appropriate rare gas abbreviation, write the condensed ground state electronic
configuration for the following species:
[5 marks]
14Si
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3_____________________________________________________________
7N
24Cr _____________________________________________________________
12Mg
8O
2+
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b) What is a Neutralisation reaction? Give an example.
[2 marks]
c) What are the three basic properties of an oxidizing agent?
[3 marks]
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Student’s ID No _________________________________
Question 4
a) In a laboratory, 6.82 g of Sr(NO3)2 (MM = 211.6 g mol-1) is dissolved in water to
form 0.500 L of solution. 0.100 L of this solution is titrated with a 0.0245 M solution
of Na2CrO4. What volume of Na2CrO4 solution is needed to precipitate all the
Sr2+(aq) as SrCrO4?
Sr(NO3)2(aq) + Na2CrO4(aq) → SrCrO4(s) + 2NaNO3(aq) [3 marks]
b) The mole fraction of N2 in dry air is 0.78. Assuming dry air is only N2 and O2,
calculate the mole fraction of O2 and the partial pressures of both gases at 760 Torr.
[4 marks]
c) Calculate the speed of a proton (mass = 1.673 x 10-24 g) that has a wavelength of
9.9 x 10-14 m s-1
[4 marks]
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Student’s ID No _________________________________
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