Concept 7 of 8Foundation

Testing food in the lab

Simple chemistry tests reveal what a food contains:

Starch test: Add a drop of iodine solution. Positive = blue-black colour.
Protein test (Biuret): Add dilute copper sulphate + caustic soda (with teacher!). Positive = violet.
Fat test: Rub food on brown paper. Positive = translucent (oily) patch.
Sugar test (Benedict's): Heat food with Benedict's reagent. Positive = brick-red.

Example

Crushed potato + iodine → blue-black (starch present). A piece of paneer + Biuret reagent → violet (protein present).

💡 Tip:Fats make paper translucent because oil fills the tiny gaps between paper fibres.