Chemistry 114
Second Hour Exam
Name:____________
(4 points)
Please show all work for partial credit
1. (12 points) Below are four kinds of crystalline solids. For each kind of solid please
tell me what the solid is composed of and what forces are used to hold it together:
Ionic
Composed of anions and cations, held together by electrostatic
interactions between oppositely charged ions.
Atomic network
Composed of individual non-metal atoms and held together by covalent
bonds between the atoms.
Molecular
Composed of molecules, depending on the structure of the molecule a
molecular solid can be held together by Hydrogen bonds, dipole-dipole interactions or
vander Waals (London) forces.
Metallic
Composed of metal atoms and held together by metallic-covalent bonds
2. (12 points) The most concentrated form of hydrochloric acid I can buy is 36% by
weight HCl.
a.) If I had 100 grams of this solution, how much HCl and how much water would
be in the solution?
36 grams of HCl
64 grams of water
b.) What is the mole fraction of HCl in this solution?
36 grams of HCl x( 1mole HCl/36.46 g) = .98 mole
64 g H2O x(1mole H2O/18 g)=3.56 mole
mole fraction = .98/(.98+3.56) =.216
c.) What is the molality of this solution?
Molality = mole/kg solvent
=.98mole/.064 kg water
=15.3m
d.) If the density of this solution is 1.2 g/ml what is the molarity of the solution?
First let’s find the volume of our 100 g solution using density
Now that we know the volume we can find the molarity = moles/liter
.98 mole/.0833 L = 11.8M
3. If a solution of Ca3(PO4)2 has a freezing point of -5o C, what is the molality of the
solution? (KF of water is 1.86 oCAkg/mol)
Freezing point depression = Kf im
Freezing point depression = freezing point pure solvent - freezing point solution
=0-(-5) = 5oC
5oC=1.86 oCAkg/mol x im
Ca3(PO4)2 ionizes to 3Ca2+ + 2PO43- i=5
5oC=1.86 oCAkg/mol x 5m
m=5oC/(1.86 oCAkg/mol x 5)
=1.86mol/kg
4. The bubbles that first form when you heat water are actually come from N2 and O2
gas dissolved in the water. These gases come out of solution because they are no
longer soluble in water once it is heated to near boiling.
(8 points) If the partial pressure of N2 is .8 atm, and the Henry’s Law constant for N2 in
water is 1.6x103atmAM-1, what s the molar concentration of N2 gas in water?
P =khenry x M
.8 atm =1.6x103 atmAmol/liter x M
M = .8 atm/1.6x103 atmAmol/liter
=.0005M
(4 points) How many mls of this gas are in 1 liter of water at 25oC and 1 atm overall
pressure?
.005 mole/liter x 1liter = .005 mole
25oC +273 = 298K
PV=nRT; V=nRT/P
V = (.0005 mol x .08206 lAatm/KAmol A298K)/1 atm
= .0122 liter
=12.2 mLs
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5. (12 points) Define the following terms:
You may skip one term!
Colligative propterties
Properties that depend on the number of particles in a solution, but not the
chemical nature of the particles
Azeotroph
A mixture of two or more liquids whose composition does not change during
distillation because the composition of the vapor is the same as the composition of the
liquid.
Liquid crystal
A state of matter that has properties of both a liquid and a crystal; It is crystal like
in that there is some degree of repeating order, but it is liquid like in that some flow can
occur.
Colloid
A substance in which small, microscopically sized particles are suspended in
another substance.
Face centered cubic cell
A crystal lattice in which one atom is centered at each corner of a cube, and one
atom is located on each face of the cube.
A negative deviation from Raoult’s law
This occurs when a solution has a lower vapor pressure than that calculated
using Raoult’s Law. Negative deviations are associated with strong solvent-solute
interactions.
Order parameter
The exponent associated with a concentration in a rate law equation.
6. (12 points) In lab you performed the reaction:
3 IO3- (aq) + 8 HSO3- (aq) + 2 H+ (aq) Y 8 HSO4- (aq) + I3- (aq) + H2O(l)
If the rate of IO3- disappearance was .005 M/sec....
A. What is rate of H+ disappearance?
B. What is rate of HSO4- appearance?
C. What is the overall rate of the reaction?
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7. The initial rate of the reaction A + B 6C was determined in three different
experiments. The results of these experiments are given in the table below:
[A] (M)
[B] (M)
0.75
0.75
1
0.75
1
1.5
rate (M/sec)
3.07
3.86
8.87
A. ( 3 points) Write the rate law for this reaction
Rate = k[A]x[B]y
B. (3 points) What is the order parameter for [A]?
C. (3 points) What is the order parameter for [B]?
D. What is the overall rate constant for this reaction?
8.87M/sec=k[1M].8[1.5]1.2
k=8.87/([1M].8[1.5]1.2)
=5.45 And the units are strange so I will ignore them
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8. Here is data from another kinetic experiment where A6 B + C. In this case the
concentration of A was followed as a function of time, and the data is given below:
Time
(seconds)
0
1000
2000
3000
4000
5000
6000
7000
[A] (M)
0.01
0.005882
0.004167
0.003226
0.002632
0.002222
0.001923
0.001695
( 4 points) Tell me how you would plot this data (X and Y Axis) to determine if this was a
zero order reaction and how would you determine the rates constant (k) from this plot?
I would plot time on the X axis and [A] on the Y axis. If I got a straight line, the
slope of the line would equal -k
( 4 points) Tell me how you would plot this data (X and Y Axis) to determine if this was a
first order reaction and how would you determine the rates constant (k) from this plot?
I would plot time on the X axis and ln[A] on the Y axis. If I got a straight line, the
slope of the line would equal -k
( 4 points) Tell me how you would plot this data (X and Y Axis) to determine if this was a
second order reaction and how would you determine the rates constant (k) from this
plot?
I would plot time on the X axis and 1/[A] on the Y axis. If I got a straight line, the
slope of the line would equal +k
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