Download Chem. 121, Sec 11 Name: Student I.D. Please Show Your Work

Chem. 121, Sec 11
Name:
Student I.D.
Please Show Your Work!
1. Balance the following chemical equation: ( 2 marks)
PCl3(l) + Cl2(g) + P4O10(s) → POCl3(l)
2. Ammonia reacts with oxygen to produce nitrogen oxide and water, according to the
following unbalanced equation: (4 marks)
NH3 (g) + O2(g) → NO(g) + H2O(l)
If 2.00 g of ammonia is reacted with 4.50 g of oxygen
a) which is the limiting reagent?
b) how much NO is formed?
c) what mass of the excess reagent remains at the completion of the reaction?
Chem. 121, Sec 11
Name:
Student I.D.
Please Show Your Work!
3. The reaction of aluminum with hydrochloric acid produces hydrogen gas. The balanced
chemical equation for the reaction is given below:
2Al (s) + 6HCl (aq) → 2AlCl3 (aq) + 3H2 (g)
If 35.5 mL of H2(g) is collected over water at 26 ◦C and a barometric pressure of 755 mmHg,
how many moles of HCl must have been consumed? (The vapor pressure of water at 26 ◦C is
25.2 mmHg.) Show your calculations; include units in every step. (5 marks)
R= 0.08206 atm.L. mol-1. K-1 , T (K) = t (◦C) + 273.15
Chem. 121, Sec 11
Name:
Student I.D.
Please Show Your Work!
4. If 4.0 ×1024 molecules of N2, 4.0 g of H2, 6.0 moles of O2 are placed in an 8.2 L
container at 127°C, what would be (i) the mole fraction of each gas, (ii) the total pressure
in the flask, and (iii) the partial pressure of each gas? (6 marks)
5. A gaseous compound containing only carbon, hydrogen and fluorine is 36.4% C and
6.10% H by mass. The density of this gas at 1.50 atmospheres and 27°C was found to be
4.025 g/L. Find the molecular formulae of the gas. (4 marks)
6. Which of the following reactions gives a positive value for the electron affinity?
Explain why? (3 marks)
2A) O- (g) + e- → O (g)
B) Cl(g) + e- → Cl- (g)
C) S(g) + e- → S-(g)
D) Br(g) + e- → Br-(g)
Chem. 121, Sec 11
Name:
Student I.D.
Please Show Your Work!
7. Which series of elements shows the smallest difference in atomic radii? Explain why?
(3 marks)
A) Li......F
B) Be......Ra
C) He......Xe
D) C......Pb
E) Sc......Zn
8. Determine the relative rates of diffusion of hydrogen gas and oxygen gas at 25◦C? (3
marks)
9. Sketch (draw) all of the orbitals with a principal quantum number equal to 2. (3 marks)
Chem. 121, Sec 11
Name:
Student I.D.
Please Show Your Work!
10. The existence of discrete (quantized) energy levels in an atom may be inferred from:
(2 marks)
A) diffraction of electrons by crystals
B) X-ray diffraction by crystals
C) atomic line spectra
D) experiments on the photoelectric effect
11. An orbital: (2 marks)
I)
describes a region of high electron density.
II) describes a region in an atom where an electron is likely to be found.
III) is a wave function resulting from specific values assigned to quantum numbers in wave
equations.
IV) describes a spherical region around a nucleus where an electron can be found.
A) II only
B) I and II
C) II and III
D) I, II, and III
E) I, II, III, and IV
12. Calculate the energy required to promote an electron in a hydrogen atom from a 4f to a 5s
orbital. (4 marks)
Chem. 121, Sec 11
Name:
Student I.D.
Please Show Your Work!
13. Show the orbital diagram for the ground state electron configuration of the following:
Cu , Mn, and Cr3+? (6 marks)
14. Why is the electron affinity so positive for the noble gas elements? Explain. (2 marks)
15. The electron in a hydrogen atom drops from a higher energy level to the third principle
shell, emitting a photon with a wavelength of 1282 nm in the process. What was the value
of n for the higher energy level? (4 marks)
Chem. 121, Sec 11
Name:
Student I.D.
Please Show Your Work!
16. List in order of more negative electron affinity: S, Cl, Li, As, Se (more positive to more
negative) . (3 marks)
17. Choose the paramagnetic atom or ion: Ca, Ne, Sc3+, Cl-, Na. Show Orbital diagrams.
(5 marks)
18. How many electrons in an atom can have the following quantum numbers. (2 marks)
a) n = 2 l = 0 ml = +1 ms = –1/2
b) n = 3 l = 2
19. Chlorine has a large negative electron affinity. Therefore, chlorine is most likely to:
(2 marks)
A) act as an oxidizing agent
B) have a small first ionization energy
C) act as a reducing agent
D) release electrons readily to other atoms
Chem. 121, Sec 11
Name:
Student I.D.
Please Show Your Work!
20. Write an orbital diagram for the ground state electron configuration of Fe 2+ and Fe 3+?
Using the orbital diagrams, explain why Fe 2+ is easily oxidized to Fe 3+? (3 marks)
21. Using the orbital diagram showing the valence electron configuration of magnesium, Mg,
aluminum, Al, phosphorous, P, and sulfur, S, explain the following exceptions:
a) Why the first ionization energy of Al is smaller than that of Mg, and b) the first
ionization energy of S is smaller than that of P? (6 marks)
22. Which of the following has the largest radius? (2 marks)
Cl-, Ar, P3-, Sc3+, K+