the extraction of caffeine from tea leaves, the organic layer was the bottom lay
ID: 525931 • Letter: T
Question
the extraction of caffeine from tea leaves, the organic layer was the bottom layer of the separatory funnel. in the extraction of spinach pigments, the organic layer was the top layer of the separatory funnel. when you encounter a two layer, how do you know which layer is aqueous and which is organic? how would you determine before mixing the two liquids if you will get two layers or just one?
determine which of the following solvents will create a two layer system with water:
dimethyl ether, dichloromethane, ethanol, ethyl acetate, n-hexane, toluene
Explanation / Answer
In organic extraction experiments, we genrally use two different solvents which are immiscible in each other. Most often we use water and other organic solvents such as diethyl ether, Hexane, ethyl acetate, DCM etc. Such kind of organic solvents are immiscible in water and hence when we mix them together it forms two different layers (even after well shaking it seprates eventually!!). This happens because of lot many reasons which includes, the difference in polarity, solubility (misciblity), and density.
As the two slovents are immiscible they form two differnt layers but how we know which is what? Now this can be predicted by two solvents density. Which ever solvent has more density it will be in the bottom layer. e.g. in the mixture of water and ethyl acetate : water has density = 1 g/ml at 25oC and ethylacetate has density = 0.902 g/ml at 25oC. Thus water is heavier then the ethyl acetate so water gets at the bottom layer and upper layer will be of ethyl acetate.
In another example, let's say we have mixture of DCM and water. Now DCM density is = 1.33 g/ml. Thus it is more heavier then the water so it will be in bottom layer whereas water will be in upper layer.
In conclusion, we can predict that which layer will be upper and lower. The solvent which has high density will be at bottom and solvent which has lower density will be in upper layer. (how to remember: heavier person always chooses lower bunk!)
Dimethyl ether (density = 0.71g/ml) is immiscible with water hence it will form two layer (water will be bottom layer)
DCM is immiscible with water hence it will form two layer (water will be top layer)
Ethenol is miscible with water hence it will not form two layers.
Ethyl acetate (density = 0.902 g/ml) is immiscible with water hence it will form two layer (water will be bottom layer).
n-Hexane (density = 0.659 g/ml) is immiscible with water hence it will form two layer (water will be bottom layer)
Toluene (density = 0.87g/ml) is is immiscible with water hence it will form two layer (water will be bottom layer)
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