oils are chains of carbon and hydrogen, if there are not enough
hydrogen molecules to satisfy the carbon molecules need for an
outer shell, the carbon molecules will bond to eachother in a c-c
double bond. this is where a bond from each carbon bonds to the
other carbon, holding the to molecules together by two bonds
instead of one.
if there are double bonds in a molecule the solution
is called unsaturated, as oppose to carbon atoms
satisfied by all the needed hydrogens.
We can test for saturation with bromine water, if a substance
is unsaturated bromine water will turn colourless. the more
double bonds are in a substance the faster the reaction.