Required practical - food tests

• What is used to test for starch?

  Iodine
• What colour is iodine to start with and what colour does it turn if starch is present?


  Start: orange

  Turns: blue/black
• What is a safety factor that should be used while doing the food test practical?


  Safety goggles must be worn
• What is the first step when doing the food test practical?


  Take the food sample and grind it with distilled water using a mortar and pestle until it makes a paste.
• What do we then do with the food paste?

  Transfer it to a beaker and add more distilled water. Stir so the chemicals in the food dissolve into the water. We then filter the solution to remove suspended food particles.
• How much food solution do we used when testing for starch?


  2cm^3
• How much iodine solution do we use during the test for starch?


  A few drops
• What colour will iodine be if theres no starch present?


  orange
• How much food solution do we use when testing for sugars?


  2cm^3
• What solution is used to test for sugars?

  benedict's solution
• How much benedict’s solution do we use when testing for sugars?


  10 drops
• What colour is benedict's solution?


  blue
• What do you do once you’ve added 2cm^3 of the food sample and 10 drops of benedict's solution?


  add the test tube into a beaker half full of hot water from a kettle.
• How long does the food sample and the benedict’s solution sample stay in the beaker of hot water?


  5 minutes
• What colour will benedict's solution be if sugars are present?


  small amount of sugar = green

  more sugar = yellow

  a lot of sugar = brick red
• What sugars does the benedict’s test work for and an example?

  Reducing sugars e.g. glucose
• What is used to test for protein?


  biuret solution
• How much biuret solution is used to test for protein in 2cm^3 of a food sample


  2cm^3
• what colour is biuret solution?

  blue
• What colour does biuret solution turn if protein is present?


  purple / lilac
• What is different when you test for lipids compared to the other tests?


  we dont filter the food sample solution because the lipid molecules can stick to filter paper
• What do we use to test for lipids?

  a few drops of distilled water and a few drops of ethanol
• What happens if lipids are present after you gently shake the test tube?


  A cloudy white emulsion forms
• What is dangerous about the test for lipids?


  ethanol is highly flammable so no naked flames can be present.