Subject: Chemistry    / General Chemistry

Page 1 of 12

Chemistry 121

The University of British Columbia

Midterm Examination II

Page 2 of 12




Possible Marks















Page 3 of 12

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. isotopes

B. allotropes

C. metalloids

D. oxides

E. None of the above

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

A. 4d ? 5f

B. 10p ? 15d

C. 3p ? 1s

D. 3p ? 4p

E. 2s ? 25p

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

A. ?1.36 ? 10?19 J

B. ?1.23 ? 10?18 J

C. 3.88 ? 10?18 J

D. 1.36 ? 10?19 J

E. 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 an electron can be measured exactly.

B. The de Broglie wavelength for a 1000 kg car travelling at 1% of the speed of light 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.





Page 4 of 12

5. The sketch below shows the radial probability distribution for an orbital with at least one nodal plane at ? = ????2. Which orbital does it represent?

A. 3py

B. 4dx2-y2

C. 3pz

D. 2s

E. 4dz2

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

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

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

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

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

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

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

A. 5, 2, 3

B. 3, 3, 2

C. 4, 2, ?2

D. 2, 2, 0

E. 2, 3, 0

8. The thermite reaction was used to break into a secure storage facility in an episode of the TV show “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 Br2 ? Al2Br6 + 32 O2

C. 2 Al + Fe2O3 ? Al2O3 + 2 Fe

D. S8 ? S2 + S6

E. Na + H2O ? NaOH + 12 H2





Page 5 of 12

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?









D. E.

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

A. Bent

B. Trigonal pyramidal

C. Tetrahedral

D. Trigonal bipyramidal

E. See-saw

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

A. 0

B. 1.92 ? 10?19 J

C. 4.10 ? 10?14 J

D. 1.07 ? 10?28 J

E. 3.55 ? 10?16 J









Page 6 of 12

Part 2. Short Answer Questions

1. Write balanced equations to represent the chemical reactions involved in each of the following 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 occurs in 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

12 marks

Page 7 of 12

(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 balanced reaction for the formation of E.

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




Page 8 of 12

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

appropriately. Indicate the sign of the phases.

3dx2 ? y2 4px

(b) Below is a sketch of the wavefunction (?) vs. z for a specific atomic orbital of

the hydrogen atom. Identify the orbital with the appropriate orbital label

(e.g. 1s, 2s, 2px, etc.).

(c) On the graph below, sketch the wavefunction (?) vs. ??for the 3dz2 orbital when the

radius (r) is not zero.

10 marks

Orbital: ____________

Page 9 of 12

4. (a) Calculate the energy of the transition between the ground state and first excited state of 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 an 8p excited state. What is the one-electron species? Show your work.

(c) When the one-electron species X decays from the 8p excited state to states with new values of n, photons with several different wavelengths are emitted. One of these transitions corresponds exactly to the energy required to excite an electron in the hydrogen atom from the ground state to the first excited state. Determine the value of n (principal quantum number) of the state to which the 8p state of X decays to give this wavelength. Show your work.

10 marks




Page 10 of 12

(d) The plot of ? vs. ? (at ? = ????2 ) for the specific orbital of X to which the 8p state decays in part (c) is given below. Identify the orbital with the appropriate orbital label (e.g. 1s, 2s, 2px, etc.).

End of Examination


Page 11 of 12

Supplementary Sheet

Potentially Useful Information

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

NA = 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 kg

ao = Bohr radius = 0.53 Å

RH = Rydberg constant = 2.18 × 10?18 J

1 eV = 1.60 × 10?19 J

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

????????= ?2.18 ×10?18 J ????2????2 ????????= ?2????28????????2

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

Cartesian and Spherical Polar Coordinates:

????2+????2+????2=????2 ????=????sin????cos???? ????=????sin????sin???? ????=????cos????

Page 12 of 12

Order Now