Lab 5.13/5.14 – Paper Chromatography

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.13_lab_cromo_paper.docx

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5.13 Introduction: Paper Chromatography
A little girl was kidnapped and ransomed. After she was successfully recovered, she assisted
police in finding where she was held captive. The room that she was in contained marker pens.
You must determine whether these marker pens were used to make the ransom note.
In this lesson, you will use paper chromatography techniques to resolve this crime.
Clues in a Kidnapping
Six-year-old Haley Jones is the daughter of Henry and Sally Jones. Mr. and Mrs.
Jones are investment bankers with a local firm and the family income exceeds $1.2
million.
On the way home from school, Haley was abducted. The next morning a ransom
note was submitted to the Jones family. The ransom note included drawings, which
looked like Haley’s work
Paper Chromatography
Were the markers used to write the ransom note?
To answer the question, you must determine whether the markers and the ransom note
use the same inks. To test the inks, you will separate the components of each marker pen
by paper chromatography.
Paper chromatography uses filter paper as the solid stationary phase. The mixture is
absorbed at the bottom of the paper. The mobile phase is liquid. As the liquid is drawn up
through the paper by capillary action, it takes the mixture with it. Each substance in the
mixture interacts differently with the paper, which affects its rate of movement.
The ratio of the distance moved by a substance to that moved by the solvent is called the
retention factor ( R f ). You will learn more about R f on the next screen.
Paper Chromatography: The different components of ink separate as the solvent travels
up the paper by capillary action.
Retention Factor
Note: This is a text version of Retention Factor. If you are able to complete the Flash version, you
do not need to complete this activity.
Directions
Retention factor is the ratio of the distance traveled by a substance in the mixture divided by the
distance traveled by the solvent.
Rf ? distance substance traveled
distance solvent traveled
Let’s find the retention factor of the red substance in this mixture.
Step 1
Note the measurement at the starting point (the point where the mixture was first applied). In this
example, the starting point is 2 cm.
Step 2
Locate the solvent front. Measure the distance between the starting point and the solvent front. In
this example, that is 7.7 cm ? 2 cm ? 5.7 cm .
Step 3
Measure the distance from the starting point to the center of the red substance. That distance is
4.8 cm ? 2 cm ? 2.8 cm .
Step 4
Calculate the retention factor. Divide the distance the substance traveled (2.8 cm) by the distance
the solvent traveled (5.7 cm).
Rf ? distance substance traveled ? 2.8 cm ? 0.49
distance solvent traveled
5.7 cm
The retention factor of the red substance is about 0.49.
Your turn
Find the retention factor of the orange substance.
Answer:
Hint
The distance the solvent traveled has not changed. So the denominator is still 5.7 cm.
Answer
The retention factor of the orange substance is approximately 0.42.
Feedback
Measure the distance from the starting point to the center of the orange substance. That distance
is 4.4 cm ? 2 cm ? 2.4 cm .
Rf ? distance substance traveled ? 2.4 cm ? 0.42
distance solvent traveled
5.7 cm
Unit 5 – Lab 5.13/5.14 – Paper Chromatography
The ‘Paper Chromatography’ Lab is our next lab in unit 5 and it is largely a virtual lab.
Overall, you are analyzing the ink from markers found at a crime scene, and you are trying
to see if the markers match the ink in a ransom note. A little girl was kidnapped, and while
she is safely at home after the transfer of ransom money, we are still trying to find out who
the kidnappers might be. You will gather info on the markers from the scene by conducting
the virtual lab. The data from the ransom note inks is provided for you in the lab
instructions.
In order to conduct this lab, you will need to print out the student guide and lab
instructions. As you read through the background information (in 5.13), make sure to take
notes on paper chromatography and make sure you have a clear understanding of how the
technique works (for example, what do we mean by mobile phase, stationary phase, and
Rf). You will start your analysis by opening the virtual lab and working through the
tutorial. Make sure to pay careful attention when working through the tutorial so you will
know what you are doing when you actually conduct the lab.
Once the tutorial is complete, you will reset the lab to start Part 1. In this part of the lab,
we are testing the 4 solvents to see which solvent is the best. The best solvent will not run
off the filter paper, but will provide a good separation of the components of the black ink
dot. You can run all 4 samples (with the different solvents) at the same time. The total
volume of solvent in each vial will need to be 10 mL (be careful counting droppers!). The
lab will actually take 20 minutes to run, and you need to be ready to stop it and analyze the
papers right when the 20 minutes is up (the solvents keep moving even when time ends).
You may need to remove the filter papers from the clips to see where the solvent ended up.
Remember, we want the solvent still on the paper, and a good separation. Only one solvent
should have these results.
Once you determine the best solvent, we will use that solvent in Part 2 to test the red,
black, and green markers. Unfortunately, you cannot run all three markers at the same time
in the same virtual lab. You can open multiple lab windows and run the inks in separate
windows. If you decided to run multiple labs at the same time, just make sure the ink
samples are staggered enough so you can complete your analysis with one ink (at the end of
20 minutes) and then be ready when the time for the next ink goes off. We need to do our
analysis as soon as the 20 minutes is up! To get your measurements, you will need to
zoom in the screen as much as possible. It will still be difficult to get exact numbers, so do
your best with your measurements. You are recording the distances as they are, and will
subtract the 2 cm when you go to calculate the Rf (see formula on page 3 of lab
instructions). Note that you will not have measurements for all of the colors for each ink.
For example, the red ink only has a pink, red and deep red.
In Part 3, you will compare your findings with the inks from the ransom note. As the note
states at the top of page 4, you are not looking for exact matches, but matches that are
close. You should ultimately find 2 of the 3 markers you tested match the ink from the
ransom note.
Do this experiment.
In this lab, you must do the following:
Part 1
Determine which solvent (water, alcohol, water-alcohol mixture (50/50), vegetable oil) is
best for separating the inks and not running off the filter paper in the time allotted.
Part 2
1. Test each marker using the solvent system that you have chosen.
2. Measure the R f values of the separated components of the ink dyes from each
marker. (Use the center of the spot in the measurements.)
3. Compare the R f values of the separated components of the ink dyes from each
marker with evidence values provided in the Laboratory Instructions.
http://k12.http.internapcdn.net/k12_vitalstream_com/CURRICULUM/928313/CURRENT_RELEASE
/VHS_CHEM_Chromo.html
Science | Laboratory Instructions | Paper Chromatography
Laboratory Instructions
Laboratory: Paper Chromatography
Materials
Supplied
•
•
•
Student Guide
Laboratory Guidelines
Paper Chromatography Virtual Lab (online)
Also Needed
•
scientific calculator (optional)
Safety
•
Review the Laboratory Guidelines before conducting the lab.
Crime Summary
Six-year-old Haley Jones is the daughter of Henry and Sally Jones. Mr. and Mrs. Jones are investment bankers
with a local firm and the family income exceeds $1.2 million. On the way home from school, Haley was abducted.
The next morning, a ransom note was submitted to the Jones family. The ransom note included drawings, which
looked like Haley’s work.
FBI agents were called in to investigate the case. They took samples of the ink in the ransom note and sent them
to a forensic lab for testing. The agents advised Henry Jones to deliver the ransom as directed. Fortunately, the
kidnappers released Haley Jones once they received the money.
The FBI agents continued their investigation of the kidnapping by questioning Haley. Her testimony led the agents
to an abandoned apartment. They found three marker pens among the evidence inside. Haley said that her
captors had given these markers to her when they asked her to draw the pictures on the ransom note.
Can forensic scientists confirm that the three markers found in the abandoned apartment were the ones used in
the ransom note? In this lab, you will use paper chromatography to analyze the markers found at the abandoned
apartment. You will calculate the retention factors for each substance in the markers. You will then compare these
retention factors to those obtained from the ransom note.
Tutorial
1. Open the Chromatography Virtual Laboratory.
2. Click View the Tutorial.
3. Complete the tutorial to learn how to conduct the virtual lab.
4. When you have finished the tutorial, click the home button and reset the lab.
Part 1: Determine the best solvent for the paper chromatography test
Procedure
Determine the best solvent for the chromatography test.
1. Click Begin the Lab. The three markers in this lab are the markers found at the abandoned apartment.
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Page 1 of 4
Science | Laboratory Instructions | Paper Chromatography
2. Test each of the solvents below for 20 minutes with black ink. Run one test with each solvent. Note how
separation occurs and if the solvent runs off the far end of the filter paper. Choose which solvent is best to
use.
•
•
•
•
Water
Water-alcohol 50/50
Alcohol 100%
Vegetable oil
3. Draw or write your results in the space below. Which solvent gives the best results?
Answer here.
Part 2: Calculate the retention factors ( R f ) for each marker
Procedure
Use the virtual lab to obtain chromatograms for each marker.
1. Choose the solvent from Part 1 that gave the best separation. Add 5 ml of the solvent to a beaker and place it
under the sample bar.
2. Place a paper strip next to the ruler and place a dot at 2 cm with the red marker. Clip the paper strip to the
sample bar.
3. Set the sample bar to the lower level so the strips of paper are in the solvent.
4. Start the timer. Let the chromatograms run for 20 minutes.
5. After 20 minutes, remove the samples from the solvent, placing the sample bar on the upper level.
6. Determine R f values using the procedure below.
7. Repeat Steps 1–6 for the black marker and for the green marker.
Determine
R f values.
1. Pick up the completed chromatogram for the red marker and place it next to the ruler. Measure the height of
the solvent front. Record this value in the table below.
2. Now look at the top pink spot. Measure the height at the center of the spot. Record the value in the table
below.
3. Repeat Step 2 for the red spot and the deep red streak on the chromatogram. Take all measurements from
the center of the spot or streak.
4. Complete the table by obtaining the measurements for the spot or streaks from the black marker and the
green marker.
5. Use the following ratio to calculate the
R f value of each substance.
Rf = distance substance traveled -2
distance solvent traveled -2
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Copying or distributing without K12’s written consent is prohibited.
Page 2 of 4
Science | Laboratory Instructions | Paper Chromatography
Paper Chromatography Results (alcohol as solvent, 20 min)
Color
Red Marker:
Distance (cm)
Red
Marker:
Rf
Black Marker:
Distance (cm)
Black
Marker:
Rf
Green Marker:
Distance (cm)
Green
Marker:
Rf
Pink
Red
Deep red
Orange
Yellow
Light green
Green
Dark blue
Light blue
Solvent
front
Part 3: Compare your R f values to the R f values from the ransom note
The table below shows the results of paper chromatography tests run on the ink from the ransom note. Compare
these results to the results you recorded for the markers. Tip: When you compare these results, you are not
looking for exact matches. There will be normal variations based on experimental techniques and measurements.
Paper Chromatography Results from Inks in the Ransom Note
100% alcohol solvent, 20 min
Marker
Color
Black Writing
Rf
Pink
Red
Rf
Green Tree
Rf
0.67
0.50
Deep red
Orange
Red Person
0.41
0.15
0.43
Yellow
0.32
Light green
0.20
Green
0.37
Dark blue
0.25
Light blue
0.15
0.15
Analyze the Results
For each question below, support your answer with evidence.
1. Why is it important to use a good solvent for paper chromatography?
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Page 3 of 4
Science | Laboratory Instructions | Paper Chromatography
Answer here.
2. Which of the markers may have been used in the ransom note?
Answer here.
3. Is the retention value class evidence or individualized evidence?
Answer here.
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Copying or distributing without K12’s written consent is prohibited.
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