Characteristics of soluble and insoluble molecules?

Answer 1

Soluable molecules tend to have similar properties to the solute - particularly with respect to the polarity (or non polarity) of the molecule and the hydrophilic/hydrophobic nature.

Insoluable molecules tend to have opposite properties.

e.g. dissolving sugar or tartaric acid in water - these molecules have the important -OH groups which can ionize in water, creating polar functional groups.

Whereas, dissolving fatty materials (long chain fatty acids) such as margarine in water - these molecules do not tend to have polar groups and have lower soluability in water. They tend to be more soluable in organic (non-polar) solvents.