General Chemistry II - CHM202
General Chemistry II - CHM202
Laboratory 1 - Introduction to Solids and Solutions
Purpose:
This laboratory is intended to familiarize you with the physical properties of solids and solutions. You
should gain a greater understanding of how atoms are spatially a
anged in solids. You will also examine
the solubility of an ionic compound as a function of temperature as well as the phenomena of
supersaturated solutions and sublimation.
Introduction:
We constantly observe matter in the form of pure elements, compounds and mixtures. Most of the things
that we observe as physical materials are either solids or liquids. Many of the solids we see have a
polymeric structure (composed of complex molecules) either natural, such as wood, or synthetic, such as
plastic. We also observe simpler materials such as sugar or salt. In addition, we observe liquid matter, like
water or solutions in water. We also observe gases, but not always with our vision. Sometimes we smell
gases or sense them in other, more subtle ways.
We know that these materials are all comprised of atoms, but how are these atoms a
anged? In this
laboratory session, you should gain some insight into how atoms and molecules are a
anged into the
materials that we observe every day.
Crystalline solids exist in an extended network of repeating structural units called a crystalline lattice
(crystals). This extended network provides stability to the solid (related to the lattice energy) and the
epeating unit is called a unit cell. We will examine the a
angement of some simple unit cells by making
models on a scale we can easily observe. In addition we will calculate the free volume in these structures
and calculate the density of some pure metals using these geometric measurements.
As you know, solutions are homogeneous mixtures of one or more compounds in a solvent. In this lab the
solvent used will be water and we will determine the solubility of potassium nitrate in water at various
temperatures and generate a solubility curve. When determining the solubility of a compound in a solvent,
we will be looking for the point at which the solution exists at its maximum concentration which is called
the saturation point. We will also examine systems where a compound exists as a liquid below its normal
melting point and a solution contains more solute than present in a saturated solution. These systems
(supersaturated solutions and supercooled liquids) are said to be thermodynamically unstable and if given
enough time will form a solid but require a seed crystal or shock to initiate crystal formation. Finally, you
will observe a demonstration of sublimation in which iodine will be converted from a solid to a gas
(sublimation) and then back to a solid (deposition).
Materials:
• Styrofoam balls
• Toothpicks
• Metric ruler
• Test tube
• 600 mL beaker
• Hot plate
• Magnetic stir bar
• Thermometer (or thermocouple)
Important Note: All data collected during the lab report must be recorded in pen.
Procedure:
A. Models of crystalline unit cells:
1. All data for this section must be recorded (in pen, of course) on the group data sheet handed out
efore class. You should not be doing calculations in the lab.
2. Using the Styrofoam balls and the toothpicks, prepare a unit cell for simple cubic, body-centered cubic
and face-centered cubic crystal lattice unit cells. (See Figure 1 for a picture.)
3. Measure and record the radius of a Styrofoam ball.
4. Measure the length of the side of each unit cell with a ruler and record in the table provided.
5. Determine the number of atoms present in each unit cell.
B. Unit cell calculations (not to be done in the laboratory):
1. Calculate the dimensions of the unit cell as a function of radius geometry (not by direct measurement)
and enter the results in the table. (Note: For the body and face-centered cubic cells, you will have to
apply the Pythagorean Theorem.)
2. Calculate the volume of each “atoms” (4/3 r3, where r = 1 unit), and record. Do not calculate using
your measurements. Simply set the radius to one (1).
3. Calculate the total volume occupied by the atoms in the unit cell (number of atoms times the volume of
each atom), and record.
4. Calculate the percentage of space by atoms (volume occupied by atoms / volume of unit cell times
100%) and the percentage of empty space. Record the results on the laboratory report..
C. Determination of the solubility curve for potassium nitrate, KNO3:
1. All data for this section must be recorded (in pen, of course) on the group data sheet handed out
efore class. You should not be doing calculations in the lab.
2. Place approximately 300 mL of water in a 600-mL beaker and add a magnetic stir bar. Heat on a hot
plate to approximately 90° C. (Note: If the water starts to boil, remove the beaker from the hot
plate, lower the heat, and allow the hot plate to cool for 2-3 minutes before replacing the beaker.)
3. Weigh and record (0.1-g accuracy) approximately 2 g of potassium nitrate and add it to a clean test
tube.
4. Pipette 5.00 mL of distilled water into the test tube.
5. Heat the test tube containing the potassium nitrate solution in the water bath until the sample
completely dissolves. Stir the solution gently with the thermometer (be sure the thermometer is clean
and dry before placing it in the test tube). It may actually save time to remove the test tube periodically
for 10-20 seconds. This will prevent the temperature from rising too far above the saturation
temperature.
6. Move the test tube and thermometer from the water bath to a test tube rack.
7. Slowly raise and lower the thermometer in the test tube and record the temperature (0.1° C accuracy) at
which you first observe a crystal. This is the saturation temperature of the potassium nitrate solution.
8. Weigh and record (0.1-g accuracy) an additional 2 g of potassium nitrate and add it to the solution in
the test tube. Do not add more water. You now have ~4 g KNO3 in 5.00 mL H2O.
9. Repeat steps 4-7 with the new, more concentrated solution. (Note: The temperature at which the first
crystal appears will be higher for higher concentrations of potassium nitrate.)
10. Repeat steps 7 & 8 two more times (making 6 g and 8 g solutions).
11. Dispose of the solution in the container provided in the laboratory.
D. Graphing the solubility curve (not to be done in the laboratory):
1. You have measured solubility in grams of KNO3 per 5.00 g of water. You must convert this to
grams/100g. DO THE MATH!
2. Enter the calculated solubility in the excel spreadsheet. After you have entered all the converted
solubility values, the graph will appear on the spreadsheet.
E. Supersaturated solutions – acetic acid, HC2H3O2, and sodium acetate, NaC2H3O2:
1. The data reported here are group observations. Be sure that the group members agree on the
observations.
2. There is a bottle of glacial (pure) acetic acid in a cold-water bath on the instructor’s desk. Remove the
ottle and record the temperature of the water bath. Compare the temperature with the freezing point of
acetic acid. Handling the bottle carefully, observe if any solid is present in the solution. Dry off the
thermometer and use the thermometer to gently stir the solution and record any observations.
3. Take a bottle/flask of supersaturated sodium acetate solution to me for approval. After I approve it,
take it to your work area.
4. Remove the stopper and drop one crystal of sodium acetate into the solution. Record your
observations.
F. Sublimation of iodine, I2:
G. The data reported here are group observations. Be sure that the group members agree on the
observations.
1. Observe the demonstration at the instructor’s desk where iodine is being sublimed. Record what you
observe about the solid in the bottom of the beaker and the solid on the watch glass.
2. Record your observations about the “air” in the beaker.
Results for Part A:
nit Cel Type Simple Cabic (om) Bodyceered Cubic Fucecntred Cubic
-
Length of a Side, | edd on | 2-92 cm | 10°35 cm
Radius of an “Atom”, XXXXXXXXXXLoem 3 Loom
Results for Part C:
ATTENTION: If you allow the potassium nitrate to dissolve before you remove the test tube from
the hot water bath, you will be here VERY LATE. Follow the directions according to the prela
lecture.
Approximate ADDED Mass TOTAL Mass Volume of Saturation temperature
mass of KNOs of KNO:s (g) of KNO; (g) water (mL) £C)
2g 199969 |! XXXXXXXXXXmL IE 395°
~e(-%+-20 | XXXXXXXXXXH.032% 5.00 mL Yg.0"
s
~6g(~g+~29 | 2.002% | [ 0y4¢ 5.00 mL. SN.
sete | (1945 [8 ora | seem 63.0°
(Parts E and F are on the reverse side of this data sheet.)
Observations for Part E:
Acetic Acid
Temperature of water bath: 0.& °C (MP of acetic acid = 166°C) [5°
Observations before shaking the bottle:
eer (2)
Observations after shaking/stiring the bottle:
mt « a]
Sodium Acetate
Observations before adding the seed crystal:
Lowe _(eusd
Observations after adding the seed crystal:
white | sec pier nf. en] on VA Shiny
net Aig luged
Observations for Part F:
Solid iodine in the beaker:
fu
¢
olid iodine in the watch glass:
fugle [ym
“Air” in the beaker:
Slo fornade movi cage gett.
Results for Parts A and B:
A: Experimental Results taken from group data (25 points)
Simple Cubic
(SC)
Body Centered Cubic (BCC)
Face Centered Cubic (FCC)
Length of a Side, l
Radius of an “Atom”,
Ratio of length to radius, l
B: Theoretical Calculations (15 points)
DO NOT USE YOUR EXPERIMENTAL MEASUREMENTS.
The atomic radius, r, is one (1) unit for the following theoretical calculations.
FOLLOW DIRECTIONS!
Simple Cubic
(SC)
Body Centered Cubic (BCC)
Face Centered Cubic (FCC)
# Atoms per Cell
(see text)
Volume of an Atom
(4/3 πr3, where r = 1 unit)
Length of a Side
(for radius = 1 unit)
Volume of Atoms in the Cell
Volume of the Unit Cell
Percent of Volume Filled
Percent of Empty Space
C. Experimental results for Part C from group data (30 points)
Mass of KNO3 added
(from your data)
Total Mass of KNO3
(Add each mass to the previous amount)
Volume of wate
Saturation temperature (°C)
Solubility of KNO3 (g/100mL)
(calculated)
5.00 mL
5.00 mL
5.00 mL
5.00 mL
Results for Part D:
An Excel spreadsheet is available on Moodle.
Insert the completed spreadsheet in your report HERE. (15 points)
Observations for Parts E & F:
Insert a copy of your group data sheet HERE. (15 points)