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Chemistry 121

The University of British Columbia

Midterm Examination II

November 13, 2014

Time: 60 minutes

Family/Last Name (printed):______________________

First Name: ___________________________________

Signature:_____________________________________

Student Number:_______________________________

INSTRUCTIONS

1. Write all answers on this examination paper, and show full details of your solutions for Part 2.2. Read each question carefully.3. Check that this examination consists of 12 PAGES PRINTED ON BOTH SIDES. The last sheet

(pages 11 and 12), containing Supplementary Information and the Periodic Table, may be detachedfor ease of use.

4. The only calculator allowed is the Sharp EL-510 model. All other calculators will be confiscated.Cell phones or other electronic communication devices are not permitted on the examination desksand must be powered off.

5. Unassembled molecular model kits may be used.

RULES GOVERNING FORMAL EXAMINATIONS1. Each examination candidate must be prepared to produce, upon the request of the invigilator or examiner, his or her UBCcard for identification.2. Examination candidates are not permitted to ask questions of the examiners or invigilators, except in cases of supposed errors or ambiguities in

examination questions, illegible or missing material, or the like.3. No examination candidate shall be permitted to enter the examination room after the expiration of one-half hour from the scheduled starting time,

leave during the first half hour of the examination. Should the examination run forty-five (45) minutes or less, no examination candidate shall be permitted to enter the examination room once the examination has begun.

4. Examination candidates must conduct themselves honestly and in accordance with established rules for a given examination, which will be articul by the examiner or invigilator prior to the examination commencing. Should dishonest behaviour be observed by the examiner(s) or invigilator(s), pleas of accident or forgetfulness shall not be received.

5. Examination candidates suspected of any of the following, or any other similar practices, may be immediately dismissed from the examination by examiner/invigilator, and may be subject to disciplinary action:

i. speaking or communicating with other examination candidates, unless otherwise authorized;ii.purposely exposing written papers to the view of other examination candidates or imaging devices;iii. purposely viewing the written papers of other examination candidates;iv. using or having visible at the place of writing any books, papers or other memory aid devices other than those authorized by the examiner(s

and,v. using or operating electronic devices including but not limited to telephones, calculators, computers, or similar devices other than those

authorized by the examiner(s) — (electronic devices other than those authorized by the examiner(s) must be completely powered down if present at place of writing).

6. Examination candidates must not destroy or damage any examination material, must hand in all examination papers, and must not take anyexamination material from the examination room without permission of the examiner or invigilator.

7. Notwithstanding the above, for any mode of examination that does not fall into the traditional, paper-based method, examination candidates shalladhere to any special rules for conduct as established and articulated by the examiner.

8. Examination candidates must follow any additional examination rules or directions communicated by the examiner(s) or invigilator(s).

Put the first lette

of your family/la

name in this box.

Please check your lecture section: ___101 (MWF 1:00 PM) Rodriguez-Nunez ___102 (MWF 2:00 PM) Wolf ___103 (MWF 3:00 PM) Wolf ___110 (MWF 10:00 AM) Berlinguette ___111 (MWF 11:00 AM) MacLachlan ___122 (T,Th 2:00 PM) Mehrkhodavandi

___133 (T,Th 3:30 PM) Crane ___188 (T,Th 8:00 AM) Crane ___199 (T,Th 9:30 AM) Monga

As the curriculum has changed for 2015, questions that are not yet relevant for the firstmidterm are indicated by "OMIT".

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Marks

Part Question Possible Marks Marks

1 22

2 1 6

2 12

3 10

4 10

Total 60

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Part 1. Multiple Choice (22 marks total)For each numbered statement below, write the letter that corresponds to the best answer in the box

provided. Use CAPITAL LETTERS only. Only the answer given in the box provided will be marked.

There is only one correct answer per question. Each question is worth 2 marks.

1. Diamond and graphite are _____________ of carbon.

A. isotopesB. allotropesC. metalloidsD. oxidesE. None of the above

2. Which of the following transitions is forbidden for a one-electron species?

A.

4d 5 f B. 10 p 15d C. 3 p 1 s D. 3 p 4 p E. 2 s 25 p

3. What is the ionization energy of an electron in the 4 p orbital of a Li2+ ion?

A. −1.36 10−19 JB. −1.23 10−18 JC. 3.88 10−18 J

D.

1.36 10−19 JE. 1.23 10−18 J

4. Which of the following statements is TRUE?

A. The Heisenberg Uncertainty Principle states that the velocity and position of anelectron can be measured exactly.

B. The de Broglie wavelength for a 1000 kg car travelling at 1% of the speed oflight is equal to the wavelength of an electron travelling at 100 km/h.

C. X-rays and microwaves travel at the same speed in a

vacuum.D. The ionization energy of sodium is exactly equal to the

binding energy of sodium determined from the photoelectric experiment.

E.

None of the above.

Answer:

Answer:

Answer:

Answer:

MIT

OMIT

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5. The sketch below shows the radial probability distribution for an orbital with at least one nodal

plane at θ =

. Which orbital does it represent?

A. 3 p y

B.

4d x2-y2 C. 3 p z D. 2 s

E. 4d z 2

6. Cesium metal has a binding energy of 202 kJ/mol. In a photoelectric experiment, a Cs metalsurface is irradiated with red light of wavelength of 630 nm. Which of the following statementsis correct?

A.

Electrons will not be ejected at any wavelength of light since the binding energyof cesium is so high.

B. Electrons are ejected when light of wavelength 630 nm is irradiated but thenumber of photons must be doubled.

C. Electrons are ejected when the wavelength of the light ischanged to 750 nm.

D. Electrons are ejected when light of wavelength 630 nm isirradiated on the metal surface.

E. Electrons are ejected when the wavelength of the light ischanged to 500 nm.

7. Which set of three quantum numbers (n, l, ml ) corresponds to a d orbital?

A. 5, 2, 3B. 3, 3, 2C. 4, 2, −2D. 2, 2, 0E. 2, 3, 0

8. The thermite reaction was used to break into a secure storage facility in an episode of the TVshow “Breaking Bad”. We also observed this reaction in class. Which of the following

reactions is the best description of the thermite reaction?

A. P4 + 3 O2 P4O6

B. Al2O3 + 3 Br 2 Al2Br 6 +3

O2

C. 2 Al + Fe2O3 Al2O3 + 2 FeD. S8 S2 + S6

E. Na + H2O NaOH +

H2

Answer:

Answer:

Answer:

Answer:

OMIT

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9. Consider the following plots of probability distribution for a particle in a one-dimensional box.Which plot represents a particle with the highest energy?

A. B. C.

D. E.

10. Sulfur dichloride, SCl2 (1 mol) reacts with chlorine gas (1 mol) and sodium fluoride (4 mol) toform a salt (4 mol) and compound X (1 mol). What is the molecular shape of X?

A. BentB. Trigonal pyramidalC. Tetrahedral

D.

Trigonal bipyramidalE. See-saw

11. The electrons of certain molecules, such as 1,3-butadiene, may be treated as particles confinedwithin a one-dimensional box. If the length of the molecule is 5.6 Å, what is the lowest kineticenergy of an electron in such a molecule?

A. 0B. 1.92 10−19 JC. 4.10 10−14 J

D.

1.07 10−28

JE.

3.55 10−16 J

Answer:

Answer:

Answer:

L

L

L

L

L

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Part 2. Short Answer Questions

1. Write balanced equations to represent the chemical reactions involved in each of thefollowing statements. It is not necessary to specify the states of the reactants or products.

(a) The production of sulfuric acid (H2SO4) from sulfur dioxide (SO2) (this process occursin two steps).

(b) The reaction to produce pure aluminum from aluminum oxide (alumina) and graphite(Hall-Héroult process).

(c) The reaction of (CH3)3GeCl (2 mol) with water (1 mol).

2. Reaction of white phosphorus (1 mol) with limited chlorine gas forms compound A (4 mol)which has trigonal pyramidal molecular shape. Reaction of A (2 mol) with oxygen gas(1 mol) forms compound B (2 mol) as the sole product. Compound B is a colourless liquid,where the oxidation state of phosphorus is +5.

(a) Write a balanced reaction for the formation of A.

(b) Write a balanced reaction for the formation of B.

6 marks

2 marks

OMIT

OMIT

OMIT

OMIT

OMIT

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(c) Which of the following is the best description of compound A? Circle the correct answer.

(i) Brønsted acid (ii) Brønsted base (iii) Lewis acid (iv) Lewis base

(d) Compound B (1 mol) reacts with water (3 mol) to produce a polar gaseous compound C (3 mol) and compound D (1 mol). Write a balanced reaction for the formation of C and D.

(e) If an electric discharge is passed through a gaseous mixture of A (2 mol) and hydrogen gas

(1 mol), compound E (1 mol) is formed along with compound C (2 mol). Write a balancedreaction for the formation of E.

(f) Draw the best Lewis structures of B, D and E. Write any non-zero formal charges on theappropriate atoms, show all lone pairs of electrons as pairs of dots and all bond pairs aslines. In structures containing Cl, the Cl atoms are terminal.

B D

E

OMIT

OMIT

OMIT

OMIT

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3. (a) Sketch cross sections of the indicated atomic orbitals on the axes below. Label the axesappropriately. Indicate the sign of the phases.

3d x 2 y 2

4p x

(b) Below is a sketch of the wavefunction () vs. z for a specific atomic orbital ofthe hydrogen atom. Identify the orbital with the appropriate orbital label(e.g. 1 s, 2 s, 2 p x, etc.).

(c) On the graph below, sketch the wavefunction () vs. for the 3d z

2 orbital when the

radius (r ) is not zero.

10 marks

Orbital: ____________

OMIT

OMIT

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4. (a) Calculate the energy of the transition between the ground state and first excited stateof a hydrogen atom (in J). Show your work.

(b) A one-electron species X in the ground state absorbs light of 5.79 nm resulting in an8 p excited state. What is the one-electron species? Show your work.

(c) When the one-electron species X decays from the 8 p excited state to states with newvalues of n, photons with several different wavelengths are emitted. One of thesetransitions corresponds exactly to the energy required to excite an electron in thehydrogen atom from the ground state to the first excited state. Determine the valueof n (principal quantum number) of the state to which the 8 p state of X decays to givethis wavelength. Show your work.

10 marks

Answer:

Answer:

Answer:

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(d) The plot of vs. (at θ =

) for the specific orbital of X to which the 8 p state decays in

part (c) is given below. Identify the orbital with the appropriate orbital label (e.g. 1 s, 2 s,2 p x, etc.).

End of Examination

Answer:

OMIT

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Supplementary Sheet

Potentially Usefu l I nformation

1 Hertz = 1 Hz = 1 s−1 = 10−6 MHz 1 J = 1 kg m2 s−2 1 m = 106 m =109 nm = 1012 pm = 1010 Å

h = Planck's constant = 6.626 × 10−34 J s N A = Avogadro's number = 6.022 × 1023 mol−1

c = speed of light = 3.00 × 108 m s−1 1 amu = 1 u = atomic mass unit = 1.66 × 10−27 kg

electron mass = 9.11 × 10−31 kg proton mass = 1.67 × 10−27 kgao = Bohr radius = 0.53 Å

RH = Rydberg constant = 2.18 × 10

−18

J1 eV = 1.60 × 10−19 J

For one-electron species: Particle in a one-dimensional box:

= 2.18 × 10− J

=

ℎ

(n = 1, 2, 3, etc.)

Cartesian and Spherical Polar Coordinates:

+ + = = sin cos = sin sin

= cos

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