A student is presented with a vial that contains methylene chloride and a satura
ID: 878971 • Letter: A
Question
A student is presented with a vial that contains methylene chloride and a saturated solution of NaCl in water. Two separate layers form, but because of the odd shape of the layers, it is a little tricky to determine which is the top and which is the bottom. In an attempt to figure it out, the student adds lots of water, so that the aqueous layer will become much much larger than the organic layer, making it easier to determine which is which. After doing this, the large layer is clearly on top. Can the student conclusively determine which of the solutions was originally on the bottom?
Explanation / Answer
It is definitely a very simple answer, worth noting that the most important property is the density for each chemical compound, as well, we know there are miscible and immiscible forces. In the case of Water and methylene chloride; these are immiscible so will form two layers; water (d=1) will be on the top and methylene chloride (d=1.33) will be on the bottom.
When you are using a solution like NaCl in water the water density will be more dense, the average of salt water is around (d=1.025) so the answer will depend on the density of water when you add the NaCl.
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