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Candy Chromatography why use salt solution?

Posted: Fri Dec 14, 2018 5:57 am
by Pkbhokie
Why do you want to use salt in a water solution for a candy chromatography experiment? Why not just plain water?

Re: Candy Chromatography why use salt solution?

Posted: Fri Dec 14, 2018 11:11 am
by MeganB
Hi Pkbhokie,

Great question! Take another look at the Introduction section to the experiment, specifically the paragraph about how the separation works:

"How does the chromatography setup separate the components in the solution? The components ideally move at different speeds as they travel through the stationary phase. This is done by adjusting the mobile and stationary phases so that they interact with different properties of the solution's components, such as their molecular size, electrical charge, or other chemical properties, to distinguish and separate them from each other. In paper chromatography, different pigments can be separated out from a solution based on the solubility of the pigments. A pigment that is more soluble (or more hydrophilic) than another pigment will generally travel farther because it will be easier for it to dissolve in the mobile phase (water) and be carried with the mobile phase along the stationary phase (filter paper). A pigment that is less soluble (or more hydrophobic), or interacts more with the filter paper than the water, will generally travel a shorter distance."

After re-reading that paragraph, can you think of why it would make a difference whether salt water or plain water is used for the mobile phase? Better yet, try it out! See what happens if you use plain water vs salt water in the experiment.

Good luck and post again if you have more questions!

-Megan

Re: Candy Chromatography why use salt solution?

Posted: Fri Dec 14, 2018 3:10 pm
by Pkbhokie
Megan, I am really not sure. I did read the introduction portion before I sought some help. The only thing I can think of is that the salt water helps the components travel through the cellulose paper easier.

Re: Candy Chromatography why use salt solution?

Posted: Fri Dec 14, 2018 3:39 pm
by MeganB
Yes, you're onto it! By using salt water instead of pure water, you will change how well the pigments are solubilized (how well they dissolve) in the liquid. If they are more soluble, they will travel farther because they would more rather stay in the liquid than interact (and sort of "stick") to the paper. If they are less soluble, they will not travel as much. I'm honestly not sure whether the pigments are more or less soluble in salt water than in pure water...I would have to try out that experiment! BUT, I can tell you that IF the pigments are all too soluble...then they will all travel all the way down the length of the paper and you won't get any separation. IF the pigments are all not soluble enough...then they will all stick to the bottom of the paper and not move anywhere, and again you won't get any separation. SO you want the solubility to be JUST RIGHT so that the pigments travel a medium distance down the paper and you can separate them out based on how far each different pigment travels. Does that make sense?