Candy chromatography

[cbenitez]

If I do the candy chromatography experiment with 3 different solvents: salt water, isopropyl alcohol and vegetable oil, do I do the experiment on 3 different color M&M's with 5 strips for each color again. So that it is 15 strips for each solvent or do you use the food colorings too? Then is the dependent variable the Rf value and the independent variable the solvent used? Can a hypothesis be "If salt water, vegetable oil, and isopropyl alcohol are used as solvents, then salt water will be the best solvent for separating the dyes into their components." or do you have to say something like " If salt water, vegetable oil, and isopropyl alcohol are used as solvents, then salt water will be the best solvent, making the dyes travel the most distance and therefore have the highest Rf values."

Please let me know, Thank you!

[deleted-140482]

Hi,

This is a great experiment, and there a couple of different ways you could go with it. In the original experiment, you are trying to answer the question "What dyes are used in the candies?" which is why you have the food coloring strips. So you can compare the Rf values from the candies to the Rf values of known dyes from the food coloring. However, you seem to be interested in one of the "make it your own options" where you look at how the solubility of dyes differs in different solvents, so unless you still want to compare those to known values, I'd say that you can leave out the food coloring "knowns."

I think your plan to do three different solvents could work well with 3 different colors of M&Ms too. While you could do three different solvents with only 1 color M&M, you wouldn't be able to generalize your findings to other colors. By using multiple colors of M&Ms, you can see whether one solvent is better than the others for multiple dyes. If you do it this way, you would need 5 strips per color per solvent, so for one color of M&Ms , you would need 5 strips in salt water, 5 strips in vegetable oil, and 5 strips in isopropyl alcohol, making 15 strips per M&M color. This would then require 45 filter paper strips. Since the kit only provides you with 40 strips at most, I think you could also decrease your replicates (this is the number of repeated tests you do for each condition, here we've been planning 5) slightly. Instead of repeating each color 5 times in each solvent, you could do it 4 times and only need 36 strips total. Don't do less than 3 replicates though, That's often considered the bare minimum.

As for your hypothesis and variables, I think you have them spot on. Either of your hypotheses seem fine to me. It's just a question of which one you are more interested in. Your independent variable is definitely the solvent used. In the case of your first hypothesis though, I would say that the dependent variable is more how well the dyes separate. Rf value is one measure of this, so you can definitely use it, but it may also be how many different colors you can count on your strip. In the case of your second hypothesis, the Rf value is definitely the right dependent variable.

I think you have a great experiment here, and I hope this helps! Please feel free to post more questions in this thread if you need any more help.
JMP

[cbenitez]

Thank you for your help. I have another question. I conducted my candy experiment with three different solvents: salt water, isopropyl alcohol and vegetable oil. Is it right to assume that the Rf values for the best solvent will be higher than the other ("not as good") solvents?
My hypothesis is that, " If salt water, isopropyl alcohol, and vegetable oil are used as solvents, then salt water will be the best solvent, making the dyes travel the most distance and therefor have the highest Rf value."

[deleted-140482]

You are exactly right that a higher Rf value will mean that the dye traveled further (relative to how far the solvent traveled), which means that the dye was more soluble in that solvent. I would tend to stay away from terms like "best" and stick with more scientific terminology like "most soluble."

You don't have to change your hypothesis, but keep in mind that it's possible that different dyes will be more soluble in different solvents, so you may not necessarily come out with one "best" solvent.

Good luck doing your experiment! Let us know how it goes.
JMP

[cbenitez]

Hi JMP,
I conducted my experiment but I still have a few questions. In the salt water,the sample spot from the brown M&M separated into bands of red dye and blue dye. Between the red and blue dye there looked to be a little yellow dye too. From my understanding, you are supposed to measure the Rf value for the red and The Rf value for the blue right?
In the isopropyl alcohol and in the vegetable oil, the brown dye did not separate into visible bands of color. Do I just measure an Rf value for how far the brown dye traveled in the isopropyl alcohol and the vegetable oil. I'm not sure what this means for my results and conclusion.

In the vegetable oil, the sample spots barely moved and the vegetable oil barely moved up to strip. It was really hard to see where the sample traveled to in order to measure the Rf value because the dye barely moved and just looked like the dye spread outwards form the sample spot just a little bit.Can you explain why it did this?

Also, should the Rf values for the red M&M sample be similar to the Rf values for the red Rf values from the brown M&M samples ( from the same solvent). Mine are not very similar and I'm worried that I did something wrong when doing my experiment. The new position of the sample dye was not always easy to see, the dye was runny.
Also, in the experiment it does not say to run each trial for a specific time period, only to "let the solvent rise up the strip until it is about 0.5cm from the top and then remove the strip from the solvent." Does how much time you let it run matter? Should each strip had been run for a specific time period?
Please let me know what you think
Thank you.

[deleted-140482]

Okay, you have quite a few questions there, so I'll take them one at a time:

1) For your brown M&M where the dyes separated into multiple colors, yes, I would measure the Rf value for ALL of the colors you see: red, blue, and yellow. What does the fact that each of these dyes traveled different distances in salt water tell you about the dyes?

2) I suspect a large part of the reason your brown dye did not separate into visible bands of color in vegetable oil has to do with the fact that you said the vegetable oil and the sample spots barely moved up the strip. It sounds like the vegetable oil was basically too thick to have much wicking action up the strip. Your brown dye didn't move either because the vegetable oil didn't travel up the strip at all, or because the brown dye simply isn't soluble in vegetable oil. If the dye spot didn't move at all but the vegetable oil did move at least a small measurable distance than your Rf value will be 0, and that's totally fine. It just tells you exactly what I just said, the dyes that make up a brown M&M are NOT soluble in vegetable oil. You don't say whether that is the same thing that happened with the isopropyl alcohol. If so, perhaps the dyes aren't soluble in that either. Otherwise, if the dye spot did travel a measurable distance but didn't separate, that tells you something different, like that the multiple dyes that make up the brown color are all equally soluble in the isopropyl alcohol.

3) Whether the Rf values for the red M&M are the same as the values for the red spot from the brown M&M depends entirely on whether the same dyes are used to make each color. It's certainly possible that they are not the same at all. Why don't you do some research to see if you can find out. You may be able to find the dyes used in the ingredients list, otherwise, I'd do some searching on the internet.

4) While it's generally a good idea to keep as many things controlled in your experiment, in this case it's not crucial that all of the strips be run for the same amount of time. In order to calculate Rf values, you are taking a ratio of the amount the dye traveled to the amount the solvent traveled. This will internally control for the amount of time you let your strips run, since a strip that was allowed to run longer would have both a longer distance for the dye AND a longer distance for the solvent. When you divide by the distance the solvent run, you basically eliminate that variable. Does that make sense?

I hope this was helpful and makes sense to you. Now I have a question for you, how many replicates did you end up doing for each sample? You tell me what happened with different experimental conditions, but you don't mention whether you repeated each condition once, twice, or more times. One of the reasons scientists always do multiple replicates is so that we can eliminate the possibility that "something weird happened that one time."

If you are seeing the same thing for all of your replicates, then I wouldn't worry too much. You have your data, now it's just time to try to understand what that data is telling you.

Again, I hope this helped, and please feel free to post again if you still have questions.
JMP

[cbenitez]

Dear JMP,
Thank you for your response. I did four replicates for each color candy in each of the three solvents and the same thing happened each time. Thanks for your help. My results make much more sense to me know. Do you think I should reword my hypothesis to say: " If salt water, isopropyl alcohol, and vegetable oil are used as solvents, then the candy dyes will be most soluble in salt water." ?
Thank you