Paper Chromatography Data Form PDF

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For CHEM 1111...

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PAPER CHROMATOGRAPHY OF FOOD COLORINGS ALL THE DATA YOU WOULD COLLECT IN THE LABORATORY TO COMPLETE THIS LABORATORY REPORT IS IN THIS DOCUMENT HIGHLIGHTED IN YELLOW ENTER YOUR ANSWERS AND INFORMATION IN THE LIGHT BLUE FIELDS

Purpose The purpose of this experiment is to use paper chromatography to separate the different food colorings found in unknown mixtures and to identify the food colorings in these mixtures.

Theory Paper chromatography is a technique that can be used to separate and identify the compounds in a mixture. This technique is commonly used to separate mixtures of sugars, amino acids, and natural pigments. In this experiment you will separate and analyze mixtures of food colorings. In paper chromatography, molecules are separated based on their different solubilities in water. In this experiment you will apply or “spot” small amounts of solutions containing food colorings onto a piece of chromatography paper. An aqueous solvent is then allowed to ascend the chromatography paper by capillary action. As this occurs the solvent will move the compounds spotted on the paper upward at different rates. Compounds in the mixture that are most soluble in water move quickly up the paper where as compounds that are less soluble in water ascend the paper more slowly. As a result the different compounds of the mixtures will be separated on the paper based on their water solubility after the solvent has moved up the paper. This process of separating the components of a mixture in chromatography is called development. The food colorings will remain colored as they ascend the chromatography paper so they can be easily seen after development.

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You will conduct the chromatography experiment is as follows. Solutions containing individual food colorings, and unknown solutions containing mixtures of different food colorings, will be applied or spotted onto a piece of chromatography paper. Then the bottom edge of the paper will be placed in the developing solvent. Once this is done the solvent will ascend the paper by capillary action. As described above, the solvent will carry the food colorings up the paper at different rates. The figure on the following page shows what your chromatography paper can look like before development and after development. Level to where solvent ascended to during experiment (the solvent front)

mixtures spotted on paper

A

B

C

D

A E

Before development

B

F Solvent level

C

D

E

F

After development

A: Food color #1; B: Food color #2; C: Food color #3; D: Food color #4; E: Mixture A; F: Mixture B

The results from this experiment show that Mixture A (spot E) contains a mixture of food coloring # 2 (spot B) and food coloring #3 (spot C). Mixture B (spot F) contains a mixture of food coloring #1 (spot A) and food coloring #4 (spot D). The example above shows that different substances travel different distances as they ascend chromatography paper and that the same substances travel the same distance. The experiment also shows that unknown mixtures can be identified using this method.

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Under a given set of conditions, a particular compound always travels a fixed distance relative to the distance that the solvent travels. The leading edge of the solvent as it ascends the chromatography paper is called the solvent front. The major conditions that affect the distance a compound travels are as follows. • • • •

The solvent The type of chromatography paper The amount of compound spotted on the paper The solubility of the compound in the solvent

The ratio of the distance a compound travels to the distance traveled by the solvent front is called the Rf value. The symbol Rf stands for "ratio to front" and is generally expressed as a decimal. Rf =

distance traveled by substance distance traveled by solvent front

The Rf values for the food colorings in the previous example are calculated below.

Level to where solvent ascended to during experiment (the solvent front)

Rf (A) =

6.0 cm

Rf (D) =

3.5 cm

2.8 cm

B

= 0.35

Rf (B) = 8.0 cm = 0.80 10.0 cm 10.0 cm R 6.0 cm = 0.60 f (C) = 10.0 cm

8.0 cm

A

3.5 cm 10.0 cm

C

D

E

F

2.8 cm 10.0 cm

= 0.28

Location where compounds where originally spotted

After development

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As you can see from this example the spots from sample E has the same Rf values as the spot from sample B and sample C, and the spots from sample F have the same Rf values as those from samples A and D. This shows that sample E is a mixture of compounds found in sample B and sample C, and sample F is a mixture of the compounds found in samples A and D. In this experiment you will analyze four food colorings and four unknown mixtures. Your goal is to determine what food colorings are present in the unknown samples.

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Materials Needed • •

• • • • • •

2% (v/v) aqueous solutions of food colorings: green, blue, red, yellow (about 5 mL per student). Four unknowns prepared by mixing different combinations of 2% (v/v) aqueous solutions of food colorings: green, blue, red, yellow (about 5 mL of each unknown per student). Unknowns should be labelled as follows. o Unknown #1 o Unknown #2 o Unknown #3 o Unknown #4 Chromatography paper: two pieces per student Tooth picks (12 per student) Developing solvent (0.1% sodium chloride solution): 10 mL per student Ruler (one per student) Aluminum foil Scissors

Procedure A. Spotting the chromatography paper and developing 1. Put on your chemical-splash safety goggles. Your goggles must be worn at all times while in the laboratory. Don't take off your goggles until you leave the laboratory. 2. Obtain a piece of chromatography paper and cut it so that it is 11 centimeters long and 12 centimeters wide. Draw a line with a pencil (not a pen) across the longer (12 cm) side of the paper that is 0.5 centimeter from the bottom edge of the paper. Use a ruler to draw the line. Make eight marks with a pencil along this line. The marks should be 0.75 centimeter from each other starting 0.75 centimeter from the 11-centimeter edge. The figure on the following page will help you prepare your chromatography paper. The figure below in not to scale. Use a ruler to draw the lines on your chromatography paper.

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3. Obtain aqueous solutions of four food colorings (blue, red, yellow, and green) and Unknown #1 and Unknown #2. Also obtain six toothpicks. The solutions should be applied to the chromatography paper using a clean toothpick for each solution. Also obtain six 150-mL beakers. Clean and dry the beakers and pour small amounts (no more than 5 mL) of the six mixtures into the six beakers. 4. To apply a solution to the paper, dip one end of a toothpick into one solution, and lightly touch the end of the toothpick to the chromatography paper at the point described in the figure on the following page. A portion of solution will be transferred to the paper as a small spot when the toothpick touches the paper. The toothpick should be touched to the paper very briefly and then removed. If the toothpick is held to the paper too long too much of the solution will be delivered to the paper which will cause the solution spot to be too large. You want the spot to be as small as possible. Continue dipping the toothpick into the solution and touching the end of the toothpick to the chromatography paper in the same location. Touch the paper with the toothpick fifteen times to apply the solution. This should deliver the appropriate amount of solution to the paper. 5. Repeat the procedure described above with the other solutions using a clean toothpick for each solution. Apply each solution fifteen times as described above. Your goal is make each spot on the chromatography paper as small as possible. Look at the spots on the paper to see if all the spots are of equal color intensity after you apply the six mixtures. If they are not apply more solution to the spots of lower intensity as described above until all the spots are of equal intensity. Be sure to apply the solutions Page 6 Marc Lord Columbus State Community College

to the correct location on the paper. Indicate the unknown mixtures that you chose on your data sheet. There will be four unknown mixtures provided to you. A figure showing what your chromatography paper should look like is below.

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6. Obtain a clean 600-mL beaker. Measure 10 mL of the developing solvent (0.1% sodium chloride solution) using your graduated cylinder and pour it into the beaker. Carefully place your chromatography paper into the beaker with the solution spots toward the bottom to start the development. Do not splash the solvent onto the paper. Place the chromatography paper in the beaker so that the paper leans slightly against the side of the beaker and so that the paper is as vertical as possible. See the figure on the following page. Incorrect placement of chromatography paper

Chromatography paper inside beaker

Correct placement of chromatography paper

Chromatography paper inside beaker

7. Cover the beaker with aluminum foil to make an air-tight seal. Be careful not to move the chromatography paper or disturb the developing solvent while you do this. The beaker and the paper should not be disturbed or moved once the paper has been placed into the beaker. 8. Remove the paper from the beaker when the solvent has ascended the chromatography paper to within about one centimeter from the top edge of the paper. This should take about fifteen minutes. Make sure the solvent front doesn’t ascend to the very top. 8. Once the development is complete, remove the paper from the beaker and quickly mark the location of the solvent front with your pencil. Record the amount of time that your chromatography paper developed on your data sheet. 9. Clean all glassware and equipment that you used during this experiment and return it to its proper location. Clean your workstation and wash your hands with soap and water before you leave the laboratory.

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Jeanna Hall Name _______________________ December 3, 2020 Date _______________________

PAPER CHROMATOGRAPHY OF FOOD COLORINGS

Prelaboratory Assignment 1. Is it safe to perform this experiment without wearing your chemical-splash safety goggles? Enter Yes or No. No

2. You perform paper chromatography of four (compounds #1, #2, #3, and #4). Your results are shown below.

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Use a ruler to measure the distances traveled by each compound in the picture above. This is the distance between the Beginning point to the center of each spot on the chromatography paper. Also measure the distance between the Beginning point and the Solvent front. Record these values in the table below. You can measure the distances in inches or centimeters, but make sure you indicate the correct units on the table. Distance traveled by compound #1

2.5cm

Distance traveled by compound #2

5cm

Distance traveled by compound #3

Distance traveled by compound #4

Distance between the Beginning point and the Solvent front

3.7cm

7cm

8.3cm

Calculate the Rf values for each compound using the values you measured. Enter your values in the table below. Rf for Compound #1 .30

Rf for Compound #2 .60

Rf for Compound #3 .45

Rf for Compound #4 .84

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3. There is a relationship between the Rf values obtained during paper chromatography and water solubility according to information in the Theory section. Use this information to answer the following questions about the figure in Question #2. a. Which compound is most soluble in water? Indicate Correct for the correct answer. Compound #1

Compound #2

Compound #3

Compound #4

Correct

b. Which compound is least soluble in water? Indicate Correct for the correct answer. Compound #1

Compound #2

Compound #3

Compound #4

Correct

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PAPER CHROMATOGRAPHY OF FOOD COLORINGS

Data Sheet A. Spotting the chromatography paper and developing 1. Your chromatography results are below.

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2. Use a ruler to measure the distances on the chromatography paper above, and complete the tables below. Amount of time you developed your chromatography paper

Distance from where you originally spotted the food colorings (the Beginning point) to the Solvent front 8.5cm

35 minutes

3. Complete the tables on the following pages for the four food colorings (red, yellow, blue and green) as follows. a) The food coloring spots separated into two or more compounds during the development. Indicate the distance that each compound traveled from the Beginning point. Remember to measure the distance from the Beginning point to the center of each spot. b) Calculate the Rf value for each compound using the distance traveled by each compound and the distance between the Beginning point and the Solvent front. Red food coloring (separated into four different compounds) Rf

Distance of compound from Beginning point 2.5cm

.29

3.5cm

.41

6.7cm

.79

7.5cm

.88

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Yellow food coloring spot (separated into two different compounds) Rf

Distance of compound from Beginning point 2.5cm

.29

6.7cm

.79

Blue food coloring spot (separated into two different compounds) Rf Value

Distance of compound from Beginning point 4.7cm

.55

5.8cm

.68

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Green food coloring spot (separated into five different compounds) Rf Value

Distance of compound from Beginning point 1.5cm

.18

2.5cm

.29

4.7cm

.55

5.8cm

.68

6.7cm

.79

4. Complete the tables on the following pages for Unknown #1, Unknown #2, Unknown #3 and Unknown #4 as follows. a) The Unknown samples separated into several compounds during the development. Indicate the distance that each compound traveled from the Beginning point. Remember to measure the distance from the Beginning point to the center of each spot. b) Calculate the Rf value for each compound using the distance traveled by each compound and the distance between the Beginning point and the Solvent front.

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Unknown #1: Rf Value

Distance of compound from Beginning point 2.5cm

.29

3.5cm

.41

4.7cm

.55

5.8cm

.68

6.7cm

.79

7.5cm

.88

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Unknown #2: Rf Value

Distance of compound from Beginning point 1.5cm

.18

2.5cm

.29

3.5cm

.41

4.7cm

.55

5.8cm

.68

6.7cm

.79

7.5cm

.88

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Unknown #3: Rf Value

Distance of compound from Beginning point 2.5cm

.29

4.7cm

.55

5.8cm

.68

6.7cm

.79

Unknown #4: Rf Value

Distance of compound from Beginning point 2.5cm

.29

3.5cm

.41

6.7cm

.79

7.5cm

.88

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PAPER CHROMATOGRAPHY OF FOOD COLORINGS

Questions 1. The Unknown samples are solutions containing one or more food colorings, and each food coloring contains several different compounds. Indicate the food colorings present in the four Unknown samples that you analyzed based on your chromatographic results. Food Coloring(s) present in Unknown #1

Food Coloring(s) present in Unknown #2

Red, Yellow, and Blue

Red, Yellow, Blue, and Green

Food Coloring(s) present in Unknown #3

Food Coloring(s) present in Unknown #4

Yellow, Blue

Red, Yellow

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