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Transcript of Investigation #5
fatos KARADENIZ AND sERINA nellickel
Which solvent (water, ethanol, or acetone) will serve as the best for the separation of food dyes?
Chromatography is a process that can be used to separate various components in a mixture.The process relies on the fact that different molecules will behave in different ways when they are dissolved in a solvent and moved across an absorbent material.
Chromatography and Polarity
Chromatography paper is a filter paper that is made of cellulose, a polymer. Cellulose is polar, therefore attracting water molecules, as well as other polar substances. As the solvent reacts with the paper, it competes for the attraction of the molecules being separated. As the molecule is being attracted to the solvent, it travels up the paper along with it.
The Rf value is a ratio of the distance of the molecule divided by the distance of the solvent. The greater the distance the molecule travels, the greater its affinity or attraction for the solvent and the greater Rf value.
(H 0) is a polar substance that has a very high purity.
(CH COCH ), is an organic solvent that can act as both polar and nonpolar. Pure acetone is a colorless, somewhat aromatic, and flammable. Acetone is capable of dissolving many fats and resins. It is used as a solvent for vinyl and acrylic resins, lacquers, alkyd paints, inks, cosmetics, and varnishes.
(C H O) is ethyl alcohol or grain alcohol. It is the type of alcohol found in alcoholic beverages. Ethanol is often mixed with gasoline in order to produce fewer harmful emissions.It is a very polar substance due to its hydroxyl (OH-) group.
Food Dyes are artificial colorings that are used in a wide variety of items from food to cosmetics. Banned in Europe, food dyes are linked to hyperactivity, learning impairment, irritability and aggressiveness in children.
Based on our research we predict that ethanol will serve as the best solvent to separate the food dye molecules because of its very high polarity.
- 10 mL graduated cylinder
- 140 mL beakers
- Chromatography paper
- Distilled water
- Food dyes (Yellow 5, Red 40, Blue 1)
- Metric ruler
- Paper clips
- Paper towels
- Watch glasses
-Tie back long hair and wear lab apron and goggles.
-Rinse immediately with soap and water if there is skin contact to the substances.
-Do not inhale solvents directly
-Be sure to wash hands after the experiment is finished.
-Dispose of all excess used materials properly according to your teachers' instructions.
1. Obtain chromatography paper and cut it evenly lengthwise.
2. Place a few drops of each food dye on separate watchglasses.
3. Prepare 10 mL of distilled water and place it in the beaker.
4. Take the prepared chromatography paper and with the pipette, add a single drop of red food dye from the watchglass towards the bottom of the paper without touching the end.
5. Take another piece of chromatography paper and repeat step 4 using blue food dye.
6. Take a third piece of chromatography paper and repeat step 4 using the yellow food dye.
7. Take the three pieces of chromatography paper and place a paper clip on each of them.
8. Cut a piece of string and thread it through the three paper clips and make the pieces of chromatography paper as even and leveled as possible.
9. Suspend the chromatography paper in the beaker taping the string to the sides of the beaker. Remember to make sure that all three pieces are spaced from each other, not too close to the sides, and touching the bottom.
10. Measure out 10mL of distilled water and carefully pour it into the beaker making sure that it doesn’t directly touch the chromatography paper. The liquid should NOT touch the colors on the paper, it should only touch the bottom part that is without the dye.
11. Cut a piece of para-film and stretch it to cover the top of the entire beaker. (This causes the container to become saturated with solvent vapor and therefore it will not evaporate into the atmosphere as it rises). Let the water travel up by itself due to capillary action.
12. After 10 minutes, remove the para-film and tape carefully removing the paper with the string. Once you have taken it out, record the data in the data tables.
13. Dispose of the excess materials safely.
14. Repeat steps 3-13 using acetone rather than distilled water.
15. Repeat steps 3-13 using ethanol instead of distilled water.
solvent that is being used:
The small red dot we had put on the chromatography paper blurred into a light pink. Afterwards, it turned to a blue color. Finally, it turned into a burnt reddish- orange color.
The yellow dot stayed yellow the whole time. However, it went from a light yellow to a very dark yellow. It ended with a dark yellow that almost looked orange.
The blue spot went from light blue to a much darke blue. It then faded out again. Then, it was darker blue again. Afterwwards, the blue turned into a reddish- orange color.
solvent that is being used:
The red dot turned into a brown color after the acetone reached it. The brown faded into orange for a short span. It then went into a light shade of blue. The blue turned to pink that ent from dark to light.
The yellow dot went fr a dark yellow to a light yellow. It then went back to a darker shade of yellow. This darker yellow then faded into a light pink color.
The blue turned to a very pale blue at first. Afterwards, it turned into a much darker blue. It remained this color for a while. I then faded into a light red- orange
solvent that is being used:
The red spot turned into a brown color. This brown faded into a very pale blue color. This blue then turned into a vibrant pink color till the end of the paper.
The yello started out as a very dark yellow and then faded into a very light yellow that almost looked orange.
The blue color did not really change throughtout the span of the paper. It stayed the same shade of bright blue. In the end, though, there was a small part that was orange.
1. Why does the water creep up the paper? Explain this.
Water creeps up the paper due to capillary action. This is when bonding of a liquid's molecules to themselves is less than the attraction to another substance the molecules are touching.
2. Baking powder is a mixture of sodium bicarbonate, cream of tartar (sodium bitartrate), and cornstarch. How are these molecules similar and different?
The molecule of the cornstarch contains only carbon atoms, hydrogen atoms, single bonds, and is relatively large. The sodium bitartrate contains a sodium ion, three hydroxyl groups, and two double bonds. The sodium bicarbonate also contains a sodium ion, but only has one hydroxyl group, one double bond, and is the smallest of the three.
3. How would you seperate this baking bowder mixture into three parts?
I would use steam distillation to separate this mixture because sodium bicarbonate (Bp: 851C ), sodium bitartrate (Bp: 141C ), and cornstarch (Bp: 400C )all have different boiling points.
4. How can molecules attract each other when they are in a mixture? Predict how ethanol woould interact with those molecules.
A colloid is a type of mixture where relatively large molecules of one substance are mixed and stable due to electric charge repulsions. The repulsion prevents clotting and promotes the even dispersion of such particles through a mixture. This repulsion occurs because colloidal particles contain an equal number of positive and negative ions, but the negative ions form a layer surrounding the particle. Thus, the particles are electrically neutral but still tend to repel one another to spread out evenly through the dispersing medium. This is because polar molecules have a net negative charge thus attracting the partial positive charge of the hydrogen molecules of water. Nonpolar molecules are very organized form of hydrocarbon, consisting of no net charges. It is then repelled by water as it struggles to fit between the partial positive and partial negative of the water molecule. This is why polar substances dissolve only in other polar substances, and nonpolar to nonpolar.
5. What does the Rf value describe on a macroscopic level? Why is this important?
On a microscopic level, the Rf value describes the rate at which a compound migrates. The Rf value is the degree of retention of a component retardation factor. It's a measurement of how the compound is interacting with both the solvent (liquid phase) and the molecule (solid phase). Since usually the solid support is hydrophobic and the solvent is hydrophilic, the Rf value gives you an indication of the hydrophobicity of the compound. A high Rf value would indicate that the substance is less polar and has traveled a greater distance and a low Rf value would indicate the opposite.
6. If the molecule had a very high affinity for the stationary phase, how would this affect the Rf value? Explain.
If a compound has a high affinity to the stationary phase it will come out slower than a compound which has a higher affinity to the mobile phase. Because of the fact that the molecule would travel less, it would have a lower Rf value.
7. What role does the mobile phase play in the distance a molecule travels in chromatography? What does the mobile phase describe?
The mobile phase describes the solvent used in the process of chromatography. The mobile phase flows through the stationary phase (the paper) and carries the components of the mixture with it, each traveling at a different rate. A less polar molecule will travel faster and higher in the mobile phase than in the stationary phase.
8. If you combined a polar solvent with a molecule that has a carbonyl group (carbon with a double-bonded oxygen) would it have a high or low Rf value? Justify your answer with what you understand if intermolecular forces.
Due to the carbonyl group, a molecule that has one would be considered polar. Due to the fact that there would be a polar solvent and molecule, the Rf value would be lower because “like” molecules attract each other.
After doing this experiment, we noticed
that acetone and water had the
greatest amount of color change.
However, the ethanol traveled the
farthest but did not have a lot
of color change. Acetone had
the highest Rf vale while distilled water had the second
highest. Ethanol had the least highest Rf value.
After completing the experiment, we realized that our hypothesis was incorrect. Ethanol was not the best separator but acetone was. In fact, based on our Rf values, we realized that ethanol was the worst solvent. After doing more research, we realized that this was because the ethanol was highly polar, therefore, it quickly moved the molecules up the paper without allowing us to see the visible separation of the food dye. However, because acetone was slightly less polar, it broke down the food dyes very slowly and allowed us to see the breakdown on the chromatography paper. Therefore, the order of the solvents from best to worst are: acetone, distilled water, and then ethanol.
We calculated the Rf values by first finding the distance of the solvent an the distance of the molecule of every food dye. Then we divided the distance of molecule by the distance of solvent to get the Rf value for each food dye. We averaged the three numbers to get the average Rf value of
1. Why did you select the solvents that you tested? Did your data support your hypothesis or disprove your hypothesis?
We selected distilled water as a solvent because we wanted to use it as a constant since it was a very common solvent. We chose acetone and ethanol because we thought it would be interesting to see the results of those solvents. Our data disproved our hypothesis.
2. What explanations can you provide for the separation of the three molecules? How was the choice of the solvent connected to the separation process?
The three molecules separated because chromatography paper is made of cellulose, a polymer. Cellulose is polar, therefore attracting water molecules, as well as other polar substances. As the solvent reacts with the paper, it competes for the attraction of the molecules being separated. As the molecule is being attracted to the solvent, it travels up the paper along with it. The choice of the solvent is important because solvents that have the perfect polarity (not too polar or too unpolar) act as the best solvent.
3. What part of the chromatography setup did the molecules interact with, stationary or mobile phase? How would you explain this interaction using intermolecular forces?
The molecules were interacting with the mobile phase. The intermolecular forces are pulling the molecules between the stationary phase, the chromatography paper and the mobile phase, the solvent. The molecules of the chromatography paper ar trying to pull the molecules to where they are while the molecules of the solvent are trying to pull the molecules with them to the top of the paper.
4. Which molecule spent the most time in the stationary phase and why?
Acetone spent the most time in the stationary phase. This is because acetone had the lowest polarity out of all of the solvents. Therefore, it didn't travel as far up as the rest of the solvents.
margin of error
There are any mistakes that we may have made throughout the experiment.
1. We may have not set the chromatography paper over the beaker evenly so all three were at an even length.
2. We may have let some of the papers stay in the beaker longer than others.
3. We may have put the para-film on too late.
4. The papers may have touched each other while in the beaker.
5. We may have made miscalculations when doing the Rf value.