Download Chemistry Exam II for Chemistry 105B - November 2008 and more Exams Chemistry in PDF only on Docsity!
Chemistry 105B Exam II November 24, 2008
I certify I have not used a programming calculator for anything other than simple mathematical
operations.
_______________________________________ (Signature)
_______________________________________ (Printed name)
Multiple choice (3 pts. each) DARKEN THE CORRECT ANSWER ON THE ANSWER SHEET.
Remember there are also 3 problems given after the 22 multiple-choice questions. Budget your time
accordingly.
- How many hydrogen atoms must bond to nitrogen to give it an octet of valence electrons?
a) 4 b) 3 c) 2 d) 1 e) 5
- Which series of ionic compounds is correctly arranged in order of increasing lattice energy?
a) MgO < CaO < SrO
b) LiCl < NaCl < NaF
c) RbCl < SrCl 2
< MgCl 2
d) CaO < SrO < SCN
e) MgCl 2
< NaCl < SrCl 2
- What is the formal charge on nitrogen in NO 3 -
N
O
O
O
a) -1 b) 0 c) +2 d) -2 e) +
- Given the electronegativities below, which covalent single bond is the most polar?
Element: H C N O
Electronegativity: 2.1 2.5 3.0 3.
a) C-H b) O-H c) N-H d) O-C e) O-N
- The central atom of which compound violates the octet rule?
a) NH 3
d) BF 3
b) SeF 2
e) CF 4
c) AsF 3
- Which of the following statements is true concerning single, double or triple bonds between carbons?
a) A double bond is longer than a triple bond.
b) A triple bond is longer than a single bond.
c) A double bond is stronger than a triple bond.
d) A single bond is stronger than a triple bond
e) A single bond is stronger than a double bond.
- The Lewis structure of HCN (H bonded to C) shows that ________ has ________ nonbonding
electron pair(s).
a) C, 1 b) N, 1 c) H, 1 d) N, 2 e) C, 2
- Which molecule possesses a tetrahedral molecular geometry?
a) PF 3
d) CO 2
b) SF 4
e)
4
ICl
c) CF 4
- The bond angles, marked a, b, and c in the molecule below, are respectively about ______, ______,
and _______.
N C C C O
H
H
O
H
H
O
H
a
b c
a) 90 , 90, 90
b) 120 , 120, 90
c) 120 , 120, 109.5
d) 109.5, 120, 109.5
e) 109.5, 90, 120
- The hybridization of five atomic orbitals results in the formation of what type of hybrid orbitals?
a) sp
2
b) sp
3
c) sp
3
d d) sp e) sp
3
d
2
- Using molecular orbital theory, the bond order of the N-N bond in the
2
2
N ion is?
a) 0 d) 2
b) 3 e) 1/
c) 1
- Elemental iodine (I 2
) is a solid at room temperature. What is the major attractive force that exists
among the I
2
molecules in the solid?
a) London dispersion forces
b) Dipole-dipole
c) Ion dipole
d) Hydrogen bonding
- Which of the following substances should have the greatest surface tension.
a) CH
4
b) CO
2
c) Kr d) H
2
O e) HCl
- What is the direct conversion of a gas to a liquid called?
a) fusion b) vaporization c) condensation d) deposition e) sublimation
YOU MUST SHOW ALL WORK ON THE ANSWER SHEET FOR THE FOLLOWING PROBLEMS
- (6 pts.) Using the Kinetic Molecular Theory, explain why viscosity is inversely proportional to
temperature, i.e. at lower temperature, the viscosity is greater and vice versa.
- (14 pts) Draw the molecular orbital diagram for
2
O showing the combination of the valence atomic
orbitals to form molecular orbitals. Calculate the bond order for the molecule. Determine if the
molecule is diamagnetic or paramagnetic. Explain the bond length and strength in
2
O relative to O 2
using your knowledge of bond orders.
- (14 pts.) A 3.0 L sample of He gas at 5.6 atm and a 4.5 L sample of Ne gas at 3.6 atm are combined
at a constant temperature of 25C into a 9.0 L flask. a) Calculate the total pressure in the flask
assuming the initial pressure in the flask was 0.00 atm. b) Calculate the partial pressure of Ne gas in
the 9.0 L flask. c) If the temperature is raised to 45C, what are the new partial pressure of Ne gas, its
mole fraction and its percentage in the gas mixture? (R = 0.
K mole
L atm
ANSWER KEY
1. B 2. C 3. E 4. B
5. D 6. A 7. B 8. C
9. D 10. C 11. D 12. B
13. E 14. A 15. D 16. C
17. A 18. C 19. E 20. A
21. D 22. C
- (6 pts.) At lower temperature the average kinetic energy of the molecules is less, i.e. they are moving
more slowly. The more slowly moving molecules have less energy to overcome the intermolecular
interactions. The molecules that are at higher temperature are moving more quickly have more
energy to overcome intermolecular interactions. Thus, at low temperature, the viscosity is high while
at high temperature the viscosity is low.
- (14 pts.) Bond order = 1/2(6-1) = 5/ O 2
is paramagnetic because it contains unpaired electrons.
O
2
has a shorter bond length and a stronger bond than O 2
due to its 5/2 bond order compared to the
bond order of 2 for O 2
. (See figure on following page.)
- (14 pts.)
a.
- 7 (2sig.figs.)
9. 0 L
- 3488 mole 0. 0821 298 K
P
n n n 1. 3488 moles
- 6621 mole
298 K
K- mole
L- atm
- 6 atm 4.5 L
n
- 6867 mole
298 K
K- mole
L- atm
5.6atm 3.0 L
n
K mole
L atm
total
total He Ne
Ne
He
b. 1. 8 atm
9. 0 L
0. 6621 mole0.0821 298 K
P
K-mole
L- atm
Ne
