Give a test that can be used to differentiate chemically between butter an cooking oil.?

Answer 1

Add bromine dissolved in heptane. Saturated butter will leave the bromine orange, but unsaturated cooking oil will turn it colourless.

Answer 2

As a cook, I'll tell you the butter will separate into two layers when melted in a pan, the butterfat layer will float on top and a salty opaque white watery layer will sink to the bottom made of proteins, lactose sugar, some water and salt. The clear oil is called clarified butter and doesn't burn at a low temperature like butter does, so is good for frying with a buttery taste. The oil is homogeneous and doesn't separate into layers. Secondly, the butter is a saturated fat and the oil is probably monounsaturated or polyunsaturated. There is a test with halogen ions that will distinguish them. Some organic chemistry major will probably write in to tell you all about it.