Download Exam 2b Key Fall 2010

Chemistry 152 Exam 2b key
Please put your name on this exam. Be sure to answer all of the questions as
completely as possible.
100 points
True / False (2 points each)
1. The smallest piece of an element that is still that element is an atom of that element.
True
False
2. Neutrons have a mass of 1 and no charge.
True
False
3. An electron can be treated as a wave or as a particle.
True graded as a freebie
False
4. Electrons orbit the nucleus.
True
False
5. The d orbitals can hold as many as 6 electrons.
False…they can hold as many as 10
Chemistry 152 Exam 2b key Pg. 2
Multiple Choice (4 points each)
6. For charged particles
a. as the distance between the charges increase, the interaction decreases
b. as the distance between the charges increase, the interaction increases
c. the distance between the charges has no effect on the interaction between them
d. the strength of the interaction depends on the sign of the charges
7. Which part of Dalton’s hypothesis is not true.
a. Matter is made of indivisible atoms.
b. Atoms of different elements are different.
c. Atoms combine in whole number ratios to form compounds.
d. Atoms can combine in different ratios to form different compounds.
8. When alpha particles were shined on a piece of gold foil in Rutherford’s experiment…
a. Most particles went through undeflected.
b. Some particles were deflected at large angles.
c. Some particles bounced back.
d. all of the above
e. none of the above.
9. The fact that atomic spectra show discrete lines rather than a continuous rainbow tells
us…
a. That electrons orbit the nucleus.
b. That an electron is treated as a wave.
c. That electrons exist in discrete energy levels.
d. That electrons are very far from the nucleus.
10. In the modern model of the atom…
a. the electron is treated as a wave.
b. the electron’s mass is not counted
c. the protons are in the nucleus.
d. all of the above
e. none of the above.
Chemistry 152 Exam 2b key Pg. 3
(10) 11. For each of the following, give the number of protons, neutrons and electrons.
P
n
e
a. 64Cu
29
35
29
b. 197Au+
79
108
78
c. 79Se2-
34
45
36
(10) 12. The newly discovered fictitious element Marium (Ma) has 125 protons. It has
two isotopes, one with 155 neutrons and the other with 157 neutrons. If the atomic mass
is 280.37, what is the percentage of each isotope?
Isotopes are: 125 + 155 = 280;
125 + 157=282;
280
282
Ma
Ma
Ave = (%282Ma)(m282Ma) + (%280Ma)(m280Ma)
280.37 = x(282) + (1-x)280
0.37 = 2x
x= 18.5 % 282Ma, 1 – x = 81.5% 280Ma
(5) 13. Within an orbital, where is the electron?
everywhere
(3) 14. How many carbon atoms in 0.0360 mole of carbon?
0.0360 mol C X 6.022 X 1023 C atoms = 2.17 X 1022 C atoms
Mol C
(2) 15. What is the mass of 1.336 moles of silicon?
1.336 mol Si X 28.0855g Si = 37.52 g Si
Mol Si
(5) 16. What is the mass of 1.665 X 1020 nickel atoms?
1.665 X 1020 Ni atoms X
1 mol Ni X
58.70 g Ni = 0.0163 g Ni
6.022 X 1023 Ni atoms mol Ni
Chemistry 152 Exam 2b key Pg. 4
(5) 17. How many moles of Fe2S3 in 4.665g of Fe2S3?
4.665 gFe2S3X 1 mol Fe2S3 = 0.02244 mol Fe2S3
207.87g Fe2S3
(10) 18. How many oxygen atoms in 6.72g of CaCO3 (100.089g/mol)
6.72 g CaCO3 X 1 mol CaCO3 X 3 mol O X 6.022 X 1023 O atoms = 1.21 X 1023 O atoms
100.089 g CaCO3 mol CaCO3
mol O
(10) 19. Describe the modern model of the atom. Be sure to include the masses, charges
and locations of all of the subatomic particles.
Protons: mass 1, charge 1, nucleus
Neutrons: mass 1, charge 0, nucleus
Electrons: mass negligible, charge -1, discrete orbitals very far from the nucleus
(10) 20. For each of the following, give an electron configuration and circle the valence.
Valence in red
a. Ba [Xe]6s2
b. Sc [Ar]4s23d
c. Mn2+ [Ar]4s03d5 or [Ar]3d5 so valence empty
d. P3- [Ar] or [Ne]3s23p6