Download First-Sample_Exam-1-Key

Chemistry 1410.005 Fall, 2010: Exam I
There are more things in Heaven and Earth, Horatio, than are dreamt of in your Philosophy.
- Hamlet on quantum mechanics
Instructions:





Time allotted is one hour and 20 minutes
All answers are multiple choice and equal weight.
On your scantron (provided), bubble in your name and student ID before handing in
Open notes, calculator. You may not use a computer or cell phone or your text.
Extra scratch paper has been provided for your convenience
Interesting Information
Proton rest mass (mp) = 1.67 x 10-27 kg
Neutron rest mass (mn) = 1.67 x 10-27 kg
Assume, for this exam, that the value of “pi” is 3.14
Avogadro’s number = 6.02 x 1023
The volume of a sphere, radius r, = (4/3) πr3
Units of length:
1 meter (m) = 102 cm
= 103 mm
= 106μm (micrometers)
= 109 nm
= 1010 Å (angstroms)
Units of mass
1 kg = 103 gr = 106 μg
Chemistry 1410.005, Fall 2010/Exam I
Page 1
1. How many neutrons are in an atom of
238
U?
a. 92 b. 238 c. 146 d. 73 e. none of the above
2. Consider an atom of deuterium (2H = D). Assuming a nuclear radius of 10-4 Å, estimate the
density of the deuterium nucleus.
a. 8 x 1014 kg/m3
b. 5 x 10-14 kg/m3
e. none of the above
c. 103 kg/m3
d. 1 x 109 kg/m3
3. Refer to Figure 1. A particle is emitted from a source, and travels between two oppositely
charged plates, with the trajectory as shown.
Plate 1
+
source
particle
trajectory
_
Plate 2
Figure 1: Trajectory of a particle between a positivelycharged and negatively-charged plate
Which of the following best describes this particle?
a. neutron
b. proton
c. hydrogen atom
d. electron e. none of the above
4. Decomposition of a compound reveals that it is 38.7% carbon by weight, 16.1% hydrogen,
and the rest nitrogen. Which of the following is a correct molecular formula?
a. HCN
b. CH3CH2NH2
c. H2CNNH2
d. CH3NH2
e. none of the above
For problems 5-8, consider the following information:
A piece of Ni, 1mm x 1 mm x 1mm, is completely reacted with F2 according to the following
reaction: Ni + F2  NiF2. The density of Ni is 8.9 g/cm3 with a mass of 58.7 g/mole. The
molecular weight of atomic F is 19 gr/mole
Chemistry 1410.005, Fall 2010/Exam I
Page 2
5. What is the mass of Ni reacted?
a. 8.9 gr
b. 89 gr
c. 0.89 gr
d. 0.0089 gr e. none of these
6. How many moles of Ni is this?
a. 1 mole
b. 5.87 x 10-3 mole
c. 1.5 x 10-4 mole
d. 1.5 mole
e. none of the above
d. 19 gr
e. none of the above
7. How many grams of F2 are consumed?
a. 1.5 gr
b. 2.85 x 10-3 gr
c. 5.7 x 10-3 gr
8. What is the oxidation state of Ni after the reaction?
a. 0
b. +1 c. +2 d.-2
e. -1
Questions 9-12 refer to the following:
Consider a reaction at the surface of a piece of Si. Only atoms at the outermost atomic layer
react. In a 1 cm2 sample, the number of Si atoms = 1 x 1015. Assume that they react with H2
according to:
Si(surface) + ½ H2(gas) Si-H(surface)
The Si atoms are reacted with 4 mg of H2.
(This reaction actually occurs during HF etching, and helps to protect the Si surface from oxide
formation during microlectronic device fabrication.)
9. How many moles of Si atoms (assume an atomic mass of 28 amu/atom) are at the surface prior
to the reaction?
a. 1 mole
b. 1x1015 moles
e. insufficient information
c. 6 x 10-8 moles
Chemistry 1410.005, Fall 2010/Exam I
d. 1.7 x 10-9 moles
Page 3
10. How many moles of H2 would be required to completely react the Si surface atoms?
a. 0.5 mole
b. 5 x 1014 moles
e. none of the above
c. 3 x 10-8 moles
d. 8.5 x 10-10 moles
11. What is the limiting reagent if the surface Si atoms are reacted with 4 mg H2?
a. Surface Si atoms b. H2 c. neither, both are completely reacted.
d. insufficient information e. How should I know?
12. What is the oxidation state of Cl in the perchlorate anion (ClO4-)?
a. -1
b. +1 c. +2
d. -2 e. none of the above.
13. 95. 7 gr of Ti completely react with O2 gas to form an oxide with a total mass of 159.7 gr.
What is the correct formula for the oxide?
a. TiO
b . Ti2O3
c. TiO2
d. Ti3O4 e. none of these
14. In question 13, what is the correct oxidation state of Ti in the product oxide?
a. 0
b. +2 c. +3
d. +4
e. -2
For Questions 15-18, you will need to balance the following reaction:
UO2(s) + HF(l)  UF4(s) + H2O(l)
14. 1 mole of UO2 was reacted with enough HF to produce 18 grams of H2O. Which is the
limiting reagent?
a. UO2
b. HF
c. neither, they are both completely reacted d. none of these
15. In the situation described in problem 14, how much HF is actually reacted?
a. 20 gr
b. 1.9 x 103 gr
c. 40 gr
d. 60 gr
e. 80 gr.
16. Which answer best describes the change in U oxidation state during the course of this
reaction?
a. 0 +4
b. +4  -4
c. +4+4 (no change)
d. +2 -4
e. none of the above
Chemistry 1410.005, Fall 2010/Exam I
Page 4
17. What is the empirical formula of a compound that contains 17.4% C by mass and the rest F?
a. CF
b. CF2
c. CF3
d. CF4
e. CF5
problems 18-19.. Tums neutralizes stomach acid (HCl) according to the following (unbalanced)
reaction:
CaCO3(aq) + HCl(aq) CaCl2(aq) + H2O(l) + CO2(g)
(Hint: for the purposes of this problem, you may regard CaCO3, HCl and CaCl2 as soluble.
CaCO3 is fairly soluble in acidic solutions.) Balance this equation, then answer the following:
18. Which of the following is the balanced, net ionic equation for this reaction?
a. Ca+2(aq) + CO32- (aq)  Ca+2 (aq)+ CO2(g)
b. CO32-(aq) + 2H+(aq)  H2O(l) + CO2 (g)
c. Ca+2(aq) + 2 Cl- (aq)  CaCl2(aq)
d. CO32-(aq)  CO2(g) + ½ O2
e. none of the above
19. In this reaction, which of the following is true?
a. C is oxidized
b. C is reduced
c. Cl is oxidized
d. Cl is reduced
e. none of the above
20. Which of the following is true of the reaction between a piece of solid Cu and a basic
solution: Cu(s) + NaOH(aq)  Na+(aq) + Cu(OH)2(solid)
a. Cu is reduced
above
b. Na is oxidized
Chemistry 1410.005, Fall 2010/Exam I
c. O is reduced d. Cu is oxidized e. none of the
Page 5
Chemistry 1410.005, Fall 2010/Exam I
Page 6