4. Activity: Data Collection in your Science Classroom: Using LabPro w/ Macintosh or Ti Calculators
Getting to Know
Presented by:
Hands-on Experiments
All experiments use:
LabPro interface
Logger-Pro software
Mac Laptop
A. Evaporation and Intermolecular Attractions
In this experiment, Temperature Probes are placed in two liquids. Evaporation occurs when the probes are removed from the liquid’s
container. This evaporation is an endothermic process that results in a temperature decrease. The magnitude of a temperature decrease
is, like viscosity and boiling temperature, related to the strength of intermolecular forces of attraction. In this experiment, you will
study temperature changes caused by the evaporation of two alcohols and relate the temperature changes to the strength of
intermolecular forces of attraction. You will use the results to predict, and then measure, the temperature change of a third alcohol
liquid.
B. Beer's Law Determining the Concentration of a Solution
The primary objective of this experiment is to determine the concentration of an unknown cobalt(II) chloride solution. You will be using
the Colorimeter shown in Figure 3. In this device, red light from the LED light source will pass through the solution and strike a
photocell. The CoCL2 solution used in this experiment has a deep blue color. A higher concentration of the colored solution absorbs more
light (and transmits less) than a solution of lower concentration.
C. pH of Household substances
In this experiment, litmus paper and a computer-interfaced pH Sensor is used to determine the pH values of household substances.
Universal indicator will be added to calibrate the colors of the universal indicator over the entire pH range.
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4a. Activity: Evaporation and Intermolecular Attractions
In this experiment, temperature probes are placed in two liquids. Evaporation occurs when the probe is removed from the liquid’s
container. This evaporation is an endothermic process that results in a temperature decrease. The magnitude of a temperature decrease
is, like viscosity and boiling temperature, related to the strength of intermolecular forces of attraction. In this experiment, you will
study temperature changes caused by the evaporation of several liquids and relate the temperature changes to the strength of
intermolecular forces of attraction. You will use the results to predict, and then measure, the temperature change for several other
liquids.
You will encounter two organic alcohols compounds in this experiment. Methanol contains carbon and hydrogen atoms, in addition to the OH functional group. Methanol, CH3OH, and ethanol, C2H5OH, are two of the alcohols that we will use in this experiment. You will
examine the molecular structure of the alcohols for the presence and relative strength of the intermolecular forces—hydrogen bonding,
dipole-dipole and dispersion forces.
MATERIALS
Power Macintosh or Windows PC
VERNIER computer interface
Logger Pro
Two temperature probes
2 pieces of filter paper (2.5 cm X 2.5 cm)
2 small rubber bands
methanol (methyl alcohol)
ethanol (ethyl alcohol)
Figure 1
Pre-Lab Exercise
Prior to doing the experiment, complete the Pre-lab table. The name and formula are given for each compound. Draw a structural
formula for a molecule of each compound. Then determine the molecular weight of each of the molecules. Dispersion forces exist
between any two molecules, and generally increase as the molecular weight of the molecule increases. Next, examine each molecule for
the presence of hydrogen bonding. Before hydrogen bonding can occur, a hydrogen atom must be bonded directly to an N, O, or F atom
within the molecule. Tell whether or not each molecule has hydrogen-bonding capability.
Procedure (Macintosh)
1.
Obtain and wear goggles! CAUTION: The compounds used in this experiment are flammable and poisonous. Avoid inhaling their
vapors. Avoid contacting them with your skin or clothing. Be sure there are no open flames in the lab during this experiment. Notify
your teacher immediately if an accident occurs.
2. Prepare the computer for data collection.
Prepare the computer for data collection by opening the Experiment-9 folder from Chemistry with Computers. Then open the
experiment file that matches the probes you are using.
On the Graph window, the vertical axis has temperature scaled from 5 to 30°C. The horizontal axis has time scaled from 0 to 500
seconds. Click on the axis of the graph to change these if your instructor ask you to change these values.
3. Roll the tips of Probe 1 and Probe 2 with square pieces of filter paper secured by small rubber bands as shown in Figure 1. Roll the
filter paper around the probe tip in the shape of a cylinder. Hint: First slip the rubber band up on the probe, wrap the paper around
the probe, and then finally slip the rubber band over the wrapped paper. The paper should be even with the probe end.
4. Stand Probe 1 in the methanol container and Probe 2 in the ethanol container. Make sure the containers do not tip over.
5. Prepare 2 pieces of masking tape, (10-cm long), to be used to tape the probes in position during Step 6.
Collect. Monitor the
6. After the probes have been in the liquids for at least 45 seconds, begin data collection by clicking
temperature for 15 seconds to establish the initial temperature of each liquid. Then simultaneously remove the probes from the
liquids and tape them so the probe tips extend 5 cm over the edge of the table top as shown in Figure 1.
Stop
7. When both temperatures have reached minimums and have begun to increase, click
to end data collection. Click the
OK
Statistics button,
, then click
to display a box for both probes. Record the maximum (T1) and minimum (T2) values for
Temperature 1 (methanol) and Temperature 2 (1-butanol). Use the command Apple-T to extend the time collection.
8. For each liquid, subtract the minimum temp. from the maximum temp. to determine ΔT, the temperature change during evaporation.
9. Roll the rubber band up the probe shaft and dispose of the filter paper as directed by your teacher.
10. Based on the ΔT values you obtained for these two substances, plus information in the Pre-Lab exercise, predict the size of the ΔT
value for 1-butanol. Compare its hydrogen-bonding capability and molecular weight to those of methanol and ethanol. Record your
predicted ΔT, then explain how you arrived at this answer in the space provided.
11. Based on the ΔT values you have obtained, plus information in the Pre-Lab exercise, predict the ΔT values for butanol. Compare the
hydrogen-bonding capability and molecular weight of methanol and ethanol to that of the previous liquids. Record your predicted
ΔT, then explain how you arrived at this answer in the space provided.
Processing the Data
1.
Which of the alcohols studied has the strongest intermolecular forces of attraction? The weakest intermolecular forces? Explain
using the results of this experiment.
2. Plot a graph of ΔT values of the two alcohols versus their respective molecular weights using the Excel program. Plot molecular
weight on the horizontal axis and ΔT on the vertical axis and predict what the ΔT for n-butanol should be.
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Activity 4a Evaporation And Intermolecular Attraction
____ / __ Score
Name (last)____________________(first)____________________
Lab Section: Day _________ Time _______
Substance
name
Chemical
Formula
methanol
CH3OH
ethanol
C2H5OH
Data table
Substance
T1 (°C)
Structural Formulas
www.chemfinder.com
T2 (°C)
Molecular Weight
ΔT (T1–T2) (°C)
Notes
methanol
Ethanol
For butanol, predict the temperature change, ΔT, during the evaporation.
Based your prediction on the experimental results.
butanol
T1 (°C)
T2 (°C)
Justify your prediction
ΔT (T1–T2) (°C)
Note: If you rip this page from the lab manual, be sure to trim the edge. (Reminder from your lab instructor)
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Hydrogen Bond
(Yes or No)
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4b. Activity: Determining the Concentration of a Solution: Beer’s Law
The primary objective of this experiment is to determine the concentration of an unknown cobalt(II) chloride solution. You will be using
the Colorimeter shown in Figure 3. In this device, orange light (470 nm) from the LED light source will pass through the solution and
strike a photocell. The CoCl2 solution used in this experiment has a blue color. A higher concentration of the colored solution absorbs
more light (and transmits less) than a solution of lower concentration. The Colorimeter monitors the light received by the photocell as
either an absorbance or a percent transmittance value.
Figure3
Figure 4
If the solutions have not been prepared for you then you will have to prepare five cobalt chloride solutions of known concentration
(standard solutions). Each is transferred to a small, rectangular cuvette that is placed into the Colorimeter. The amount of light that
penetrates the solution and strikes the photocell is used to compute the absorbance of each solution. When a graph of absorbance vs.
concentration is plotted for the standard solutions, a direct relationship should result, as shown in Figure 4. The direct relationship
between absorbance and concentration for a solution is known as Beer’s law.
The concentration of an unknown CoCl2 solution is then determined by measuring its absorbance with the Colorimeter. By locating the
absorbance of the unknown on the vertical axis of the graph, the corresponding concentration can be found on the horizontal axis
(follow the arrows in Figure 4). The concentration of the unknown can also be found using the slope of the Beer’s law curve.
MATERIALS
Power Macintosh with Excel program
Vernier computer interface
Logger Pro
Vernier Colorimeter
Vernier cuvette
tissues (preferably lint-free)
CoCl2 solution of 0.10 M, 0.050 M, 0.020 M and 0.010M
Stirring rod
pipet pump or pipet bulb
distilled water
test tube rack
two small beakers
Procedure (Macintosh)
1.
Obtain and wear goggles! CAUTION: Be careful not to ingest any cobalt(II) chloride solution or spill any on your skin. Inform your
teacher immediately in the event of an accident.
2.
If the cobalt(II) chloride solution has not been prepared previously, prepare a 0.10 M solution using 1.30 g of CoCl2 in 100ml
solution. Using this solution as the stock, prepare 0.050 M, 0.020M and 0.010M solution of cobalt(II) chloride. If you are not
familiar about serial dilution go to: http://www.woodrow.org/teachers/esi/2002/Biology/Projects/lab_skills/ls8/
3.
Open the file “Exp 11 Colorimeter” in the Experiment 11 folder of Chemistry with Computers. The vertical axis has absorbance
scaled should be set to autoscale. Adjust the horizontal axis so that the concentration scaled reads from 0 to 0.10 mol/L.
4.
You are now ready to calibrate the Colorimeter. Prepare a blank by filling a cuvette 3/4 full with distilled water. To correctly use a
Colorimeter cuvette, remember:
All cuvettes should be wiped clean and dry on the outside with a tissue.
Handle cuvettes only by the top edge of the ribbed sides.
All solutions should be free of bubbles.
Always position the cuvette with its reference mark facing toward the white reference mark at the right of the cuvette slot on the
Colorimeter.
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5.
Calibrate the Colorimeter.
Holding the cuvette by the upper edges, place it in the cuvette slot of the Colorimeter.
If your Colorimeter has an AUTO CAL button, set the wavelength on the Colorimeter to 565 nm (Green), press the AUTO CAL
button. For this experiment, you will be recording the absorbance at 470 nm.
6.
Collect. Empty the water from the cuvette.
You are now ready to collect absorbance data for the five standard solutions. Click
Using the most dilute solution, rinse the cuvette twice with ~1-mL amounts and then fill it 3/4 full. Wipe the outside with a tissue
and place it in the Colorimeter. After closing the lid, wait for the absorbance value displayed on the monitor to stabilize. Then click
Keep , type “0.010M” in the edit box, and press the ENTER key. The data pair you just collected should now be plotted on the
graph.
7.
Discard the cuvette contents as directed by your teacher. Rinse the cuvette twice with the Test Tube 2 solution, 0.020 M CoCl2,
and fill the cuvette 3/4 full. Wipe the outside, place it in the Colorimeter, and close the lid. When the absorbance value stabilizes,
Keep , type “0.16” in the edit box, and press the ENTER key.
click
8.
Repeat the Step 7 procedure to save and plot the absorbance and concentration values of the solutions in Test Tube 3 (0.050 M) as
Stop .
well as the stock 0.100 M CoCl2. When you have finished with the unknown solution, click
9.
Next take the absorbance of your unknown. Obtain about 5 mL of the unknown CoCl2 in another clean, dry, test tube. Record the
number of the unknown in the Data and Calculations table. Rinse the cuvette twice with the unknown solution and fill it about 3/4
full. Wipe the outside of the cuvette, place it into the Colorimeter, and close the lid. Read the absorbance value displayed in the
Collect to read the absorbance
Meter window. (Important: The reading in the Meter window is live, so it is not necessary to click
value.) When the displayed absorbance value stabilizes, record its value in 5 of the Data and Calculations table.
10. In your Data and Calculations table, record the absorbance and concentration data pairs that are displayed in the Table window.
Download the excel spreadsheet and copy and paste the Vernier data into the Excel spreadsheet.
11.
Examine the graph of absorbance vs. concentration. To see if the curve represents a direct relationship between these two
variables, work the data so that there is a graph and then add a trend line to obtain a best-fit linear regression line. This line
should pass near or through the data points and the origin of the graph.
12. Discard the solutions as directed by your teacher. Proceed directly to Steps 1 and 2 of Processing the Data.
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Activity 4b: Determining the Concentration of a Solution; Beer’s Law
____ / __ Score
Name (last)____________________(first)____________________
Lab Section: Day _________ Time _______
Processing the Data
1.
Use the following method to determine the unknown concentration. With the linear regression curve still displayed on your graph,
choose Interpolate from the Analyze menu. A vertical cursor now appears on the graph. The cursor’s x and y coordinates are
displayed at the bottom of the floating box (x is concentration and y is absorbance). Move the cursor along the regression line until
the absorbance (y) value is approximately the same as the absorbance value you recorded in Step 12. The corresponding x value is
the concentration of the unknown solution, in mol/L.
2.
Print a graph of absorbance vs. concentration, with a regression line and interpolated unknown concentration displayed. Print a copy
of the Graph window. Enter your name(s) and the number of copies of the graph you want.
3.
In addition get the Beer's Law equation, A = εbc. If b is 1.0 cm, what is the value of ε. What is the correlation
factor, "R" for your data?. Note that λ = 570 nm.
DATA and calculations
Unknown No. __________
Trial Standard solution CoCl2 (aq)
Concentration (mol/L)
1
0.0100
2
0.020
3
0.050
4
0.10
5 Unknown solution:
Concentration of unknown
Absorbance
__________
mol/L
Note: If you rip this page from the lab manual, be sure to trim the edge. (Reminder from your lab instructor)
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4c. Activity: pH of Household substances
Many common household solutions contain acids and bases. Acid-base indicators, such as litmus and red cabbage juice, turn different
colors in acidic and basic solutions. They can, therefore, be used to show if a solution is acidic or basic. An acid turns blue litmus paper
red, and a base turns red litmus paper blue. The acidity of a solution can be expressed using the pH scale. Acidic solutions have pH
values less than 7, basic solutions have pH values greater than 7, and neutral solutions have a pH value equal to 7
MATERIALS
Power Macintosh or Windows PC
Vernier computer interface
Logger Pro
Vernier pH Sensor
paper towel
household solutions
7 small test tubes
test-tube rack
red and blue litmus paper
red cabbage juice
ring stand
utility clamp
sensor soaking solution
sensor soaking solution
stirring rod
wash bottle
distilled water
250-mL beaker
Procedure
1.
Obtain and wear goggles. CAUTION: Do not eat or drink in the laboratory.
Part I Litmus Tests
2.
Label 7 test tubes with the numbers 1-7 and place them in a test-tube rack.
3.
Measure 3 mL of vinegar into test tube 1. Refer to the data table and fill each of the test tubes
2-7 to about the same level with its respective solution. CAUTION: Ammonia solution is toxic.
Its liquid and vapor are extremely irritating, especially to eyes. Drain cleaner solution is
corrosive. Handle these solutions with care. Do not allow the solutions to contact your skin or
clothing. Wear goggles at all times. Notify your teacher immediately in the event of an accident.
4.
Use a stirring rod to transfer one drop of vinegar to a small piece of blue litmus paper on a paper
towel. Transfer one drop to a piece of red litmus paper on a paper towel. Record the results.
Clean and dry the stirring rod each time.
5.
Test solutions 2-7 using the same procedure. Be sure to clean and dry the stirring rod each time.
Part II Universal Indicator
6.
After you have finished the Part I litmus tests, add 3 drops of universal indicator to each of the 7 test tubes. Record your
observations. Dispose of the test-tube contents as directed by your teacher.
Part III pH Tests
7.
Prepare the computer to monitor pH by opening the file in the Experiment 21 folder of Chemistry with Computers. The Meter
window will display live pH readings.
8.
Raise the pH Sensor from the sensor storage solution and set the solution aside. Use a wash bottle filled with distilled water to
thoroughly rinse the tip of the sensor as demonstrated by your instructor. Catch the rinse water in a 250-mL beaker.
9.
Before measuring the pH of the test solutions be sure to calibrate the pH probes with pH 4 and pH 10 buffered solution. You will
need to go under the calibration menu for this procedure.
10. Get one of the 7 solutions in the small container supplied by your sensor. Raise the solution to the pH Sensor and swirl the solution
about the sensor. When the pH reading stabilizes, record the pH value.
11.
Prepare the pH Sensor for reuse by rinsing the pH probe with distilled water from a wash bottle. Place the sensor into the sensor
soaking solution and swirl the solution about the sensor briefly. Rinse the probe again with distilled water.
12. Determine the pH of the other solutions using the Step 9 procedure. You must clean the sensor, using the Step 10 procedure,
between tests. When you are done, rinse the tip of the sensor with distilled water and return it to the sensor soaking solution.
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Activity 4c: pH of Household substances
____ / __ Score
Name (last)____________________(first)____________________
Lab Section: Day _________ Time _______
Data Table
Test
Tube
Solution
1
vinegar
2
ammonia
3
lemon juice
4
soft drink
5
drain cleaner
6
detergent
7
baking soda
Blue Litmus
Red Litmus
Hydro Ion Paper
Universal Indicator (Color)
Processing the Data
1.
Which of the household solutions tested are acids? How can you tell?
2.
Which of the solutions are bases? How can you tell?
3.
What color(s) is universal indicator in acids? In bases?
4.
Can universal indicator be used to determine the strength of acids and bases? Explain.
5.
List advantages and disadvantages of litmus and universal indicators.
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pH
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