Question

why can you not always accurately determine position of layer by checking density of water and organic compound?

Answer 1

Non polar organic compounds are immiscible with water and they only on addition with water forms different layers depending on their densities. More denser at bottom and less denser at upper layer.

But not all organic compounds are non polar and hence not all are water immiscible.

Some organic compounds are highly miscible with water. E.g. Organic molecules capable of forming strong Hydrogen bonding with water are highly miscible with water and with water they forms a single phase (and not the layer) irrespective of their densities.

e.g. organic acids like Acetic acid, Citric acid, amino acids, organic bases like amines , even some neutral molecules like alcohols are also miscible with water.

Some long chain organic comounds like fatty acids, lipids are amphiphatic in nature i.e. they can exist in both phases at the same time i.e. aqueous(polar) and organic (non-polar).

Hence we cannot always determine position of layer by checking density of water and organic compound.   

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