Chemistry 130
Practice Exam 2
November 1, 2002
Dr. Nash
100 Points Possible
NAME:__________________
1. HCN (hydrogen cyanide)
(a) draw the proper Lewis Structure, assign formal charges to the atoms.
(b) What is the electronic geometry around the central atom (circle one)
tetrahedral, trigonal planar, linear
(c) What is the molecular geometry around the central atom (circle one)
tetrahedral, trigonal pyrimidal, bent, trigonal planar,
linear?
(d) Are the bonds in the molecule polar or nonpolar (circle one)
(e) Is the molecule polar or non-polar (circle one)
(f) Would this molecule be more like to dissolve in water or benzene (circle one)
2. CH2Cl2 (methylene chloride, also a common dry-cleaning agent)
(a) draw the proper Lewis Structure, assign formal charges to the atoms
(c) What is the electronic geometry around the central atom (circle one)
tetrahedral, trigonal planar, linear
(d) What is the molecular geometry around the central atom (circle one)
tetrahedral, trigonal pyrimidal, bent, trigonal planar,
linear?
(g) Are the bonds in the molecule polar or nonpolar (circle one)
(h) Is the molecule polar or non-polar (circle one)
(i) Would this molecule be more like to dissolve in water or benzene (circle one)
3. (CH3)2O (Dimethyl ether- knocks you out) hint: O is the central atom here
(a) draw the proper Lewis Structure, assign formal charges to the atoms
(c) What is the electronic geometry around the central atom (circle one)
tetrahedral, trigonal planar, linear
(d) What is the molecular geometry around the central atom (circle one)
tetrahedral, trigonal pyrimidal, bent, trigonal planar,
linear?
(g) Are the bonds in the molecule polar or nonpolar (circle one)
(h) Is the molecule polar or non-polar (circle one)
(i) Would this molecule be more like to dissolve in water or benzene (circle one)
4. H3O+ (hydronium ion, we will talk about this next week)
(a) draw the proper Lewis Structure, assign formal charges to the atoms
(c) What is the electronic geometry around the central atom (circle one)
tetrahedral, trigonal planar, linear
(d) What is the molecular geometry around the central atom (circle one)
tetrahedral, trigonal pyrimidal, bent, trigonal planar,
linear?
(g) Are the bonds in the molecule polar or nonpolar (circle one)
(h) Is the molecule polar or non-polar (circle one) NOT A GOOD QUESTION
(i) Would this molecule be more like to dissolve in water or benzene (circle one)
5. Cl2CO (Chloroform- will also knock you out)
(a) draw the proper Lewis Structure
(c) What is the electronic geometry around the central atom (circle one)
tetrahedral, trigonal planar, linear
(d) What is the molecular geometry around the central atom (circle one)
tetrahedral, trigonal pyrimidal, bent, trigonal planar,
linear?
(g) Are the bonds in the molecule polar or nonpolar (circle one)
(h) Is the molecule polar or non-polar (circle one)
(i) Would this molecule be more like to dissolve in water or benzene (circle one)
7. Rank the following compounds by decreasing soluability in water. (we'll talk about
this on Monday)
I.
II.
III.
IV.
V.
CH3OH
C8H17OH
C3H7OH
C6H6
C16H33OH
10. Rank the following solvents in order of decreasing ability to dissolve a sample of
toluene. Again, we'll talk about this on Monday/Wednesday
I.
II.
III.
IV.
V.
C5H11OH, pentanol
Toluene (pictured at the right)
C2H5OH, ethyl alcohol
H2O, water
CH3OH, methyl alcohol
11. Rank the compounds in question 9 (above) in order of decreasing ability
to participate in hydrogen bonding
12. Water is (obviously) a very important substance. Please describe the role of
electronic and molecular geometry, bond and molecular polarity, and hydrogen bonding
on the structure of water both as a molecule and as collection of molecules in a liquid.
.
15. For each of the following atoms or ions, circle the one that has higher ionization
energy.
(a) Rb+ or Kr
(b) Br- or Kr
(c) Sr2+ or Rb+
(d) Sr or Rb+
(e) Br- or Cr2+
Kr, Rb+, Br-, and Sr2+ have something in common, what is it?
1. Consider the following molecule. This is not a Lewis structure, I've simply laid out
the the framework indicating positions of each of the atoms. Note: I've given you one
bond and the formal charge on one atom.
O
C
H
O
C
C
N
-
H
C
O
O
2. Do you all remember that Godawfull smell you experience about halfway through lab
the other day. That substance you were smelling is called triethylamine. It has a
molecular formula N(C2H5)3.
(a) Draw a Lewis structure for this thing.
(b) What is the electronic geometry and molecular geometry around the nitrogen atom.
(c) What are all of the intermolecular forces present in this molecule? Which one is most
important (Justify your answer).
(d) Is this molecule likely to be more soluable in water or octane (C8H18). Again, justify
your answer.
(h) Is this compound, triethyl amine, involved in hydrogen bonding? Explain.
5. Which of the following are reasons for the importance and strength of hydrogen
bonding? There may be more than one.
(a) in hydrogen bonding, the hydrogen is connected to a very electronegative
element
(b) hydrogen is very electronegative
(c) hydrogen is a very common element and is a major component of water
(d) hydrogen is a small atom so the partial charge separation (polarity) of the bond
is concentrated into a very small space
(e) hydrogen bonding gives rise to increased van der waals forces.
6. Rank the following
F, C, O, N
in terms of
(a) increasing ionization energy
(b) increasing atomic radius
(c) increasing electron affinity
(d) increasing electronegativity
11. Draw the Lewis structure for the following compounds
(a) Phosphorous trichloride PCl3
(b) Hydrogen thiocyanade, HSCN
(c), N2F2
(d) dichloroformaldehyde COCl2
11. Nitrate ion, NO2-
(a) Draw the Lewis Structure for this molecule.
(b) How many reasonance structures does the nitrate ion have?
(c) How many lone pairs on the nitrogen?
11. Draw the Lewis structure for the following compounds
(a) Hydrazine, N2H4
(b) Thiocyanade ion, SCN-
(c) Hydrazone, N2H2
(d) Chloroform. HCClO
7. Discuss the trend in atomic radius as one travels from left to right across a row of the
periodic table.
8. For each of the following atoms or ions, circle the one that has higher ionization
energy.
(a) Ne or Kr
(b) Br- or I(c) Ba2+ or Cs+
(d) O2- or F(e) Br- or Se2-
10. Draw the Lewis structure for the following compounds
(a) Ammonia, NH3
(b) Nitrous acid, HNO (remember the rules for finding central atoms here)
(c) Nitrogen gas, N2
(d) Oxygen Gas, O2
(e) Fluorine Gas, F2
11. Methanol, CH3OH, is a common substance known as grain alcohol. This molecules
has two ‘central atoms’.
(a) Draw the Lewis Structure for this molecule.
(b) How many unshared pairs of electrons are on the oxygen?
(c) How many are on the carbon?
3. (CH3)2O (Dimethyl ether- knocks you out) hint: O is the central atom here
(a) draw the proper Lewis Structure
6. Rank the following compounds by decreasing soluability in water.
I.
II.
III.
IV.
V.
CH3OH
C8H17OH
C3H7OH
C6H6
C16H33OH