Organic Layer Vs. Aqueous Layer (Lab Question)?

Question

I'm reading over some sources over the comparisons when using the water drop technique. I am, however, confused because I don't understand the concept of "if the upper layer is aqueous, these drops will be miscible with the water in the test tube and will dissolve, but if the upper layer is organic, the droplets will not dissolve."

My translation would be if drop of water dissolves half-way, top layer is organic and bottom is aqueous. if water, however, dissolves all the way down, top layer is aqueous and bottom is organic. Does it have to do with density being greater at the bottom? Am I even making sense? someone help me go in the right direction. I get confused about the simplest things! thanks

Answer 1

It's a little bit hard to understand out of the full context of your text or whatever you are drawing from, but here is my interpretation:

It sounds like you are sitting there with a test tube that contains two layers -- an aqueous layer and an organic layer, but that you don't know which layer is which (top or bottom). If you drip a drop of water into the test tube, one of two things will happen. Either:

1) The drop will immediately dissolve as soon as it hits the top layer of liquid. In that case, the top layer is your aqueous layer!

-or-

2) The drop will not dissolve when it hits the top layer of your test tube, but instead will probably sink as a droplet down through the top layer. When that drop reaches the lower layer, it should dissolve. That is because the top layer is the organic layer, and the lower layer is aqueous.



Most of the time your top layer will be organic, because most common organic solvents used for extractions are less dense than water. However, certain organic solvents (like dichloromethane) are heavier than water, and in that case would be the lower layer.

Answer 2

This sounds to me like you are trying to identify whether the top or bottom layer of two layers is organic or not. This is the usual procedure. You take a drop of the upper layer and add it to a test tube. If it dissolves, it too is water. You do that with both layers. The one that dissolves in water is the water layer.



I think the disparity in reasoning is that the organic layer may be the top or bottom layer and when a drop is added to the water, it may be difficult to always see the formation of a second layer from a single drop. That is why it is useful to do both layers. It is often easier to see the water layer dissolve than to see a tiny second layer on top.



While it is true that organic compounds are generally lighter than water, it doesn't matter in the lab. If you are doing an isolation, all that matter is what you do in that case, not in general. That also leads to the lab rule of don't dispose of any of your layers until you have isolated your product. If you misjudged, you can always go back. What might that rule tell you about choosing the upper or lower layer? Do you think anyone ever made a mistake?

Answer 3

Organic Layer

Answer 4

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Your prediction of properties is correct. An organic acid is reasonably polar and so might have more of an affinity for the aqueous layer than would otherwise be predicted. However, the organic acids will dimerize doubling the effective size of the organic molecule and making the dimer much more non-polar than would otherwise be anticipated. This will increase solubility in the organic layer. Sodium benzoate is fully ionized and cannot dimerize. So it will, I believe, be relatively insoluble in the organic layer.

Answer 5

By definition organic compounds are not soluble in water. By definition salts are soluble in water.

Miscible means it will dissolve completely, you can't tell them apart, water and the miscible substance. If the upper layer is organic, the droplets wont dissolve, and they will sink given their density is higher than the organic compounds.



Yes, look up the densities, the lowest density will float.