food tests

• Benedict's


  Chemical used to test for starch
• Colour with Benedict's


  • Red (if a lot of sugar)
  • Green/yellow (if a little sugar)
• The order of colour change with Benedict's is high sugar to low sugar
• You need to use heat when testing for sugar
• Biuret


  Chemical used to test for protein
• Biuret goes a certain colour if protein is present
• Iodine


  Chemical used to test for starch
• Iodine goes black if starch is present
• You don't need to use heat when testing for starch and protein
• Active site


  The 'dent' in an enzyme into which the substrate fits
• There is a graph to show how pH affects the rate of enzyme action
• Testing For Starch


  1. Put a few drops of starch solution on a spotting tile

  2. Add a few drops of iodine
• Testing for sugar (glucose)

  1. Pour some sugar solution into a test tube

  2. Add a few drops of benedict's solution

  3. Heat in a water bath
• Order of colour change with Benedict's sugar test

  • high = red
  • low = green
• Testing for protein


  1. Pour some protein solution into a test tube

  2. Add a few drops a few drops of Biuret solution and note any colour
• Testing for lipids (fat)


  1. Add a few drops of cooking oil into a test tube

  2. Add 2cm3 ethanol and shake

  3. Add 2cm3 water and shake again
• food Tests

  • starch: Add a drop of iodine
  • lipids:Place the food in a test tube. Add a few drops of ethanol , shake well. Then add a small amount of water .
  • sugar: Place the sample in a test tube. Boil with Benedict's solution. Heat in a water bath for 5 minutes.
  • protein:Place the sample in a test tube. Cover with Biuret solution and gently shake.
• Observations


  • starch ____ goes blue / black
  • It turns white
  • It turns from blue (the colour of Benedict's) to green, then yellow and then red. Note: low sugar conc. Gives green, and high sugar gives red
  • It turns from pale blue (the colour of Biuret) to purple if protein is present
• Independent variable


  The variable that is deliberately changed in an experiment
• Dependent variable


  The variable that is measured in an experiment
• Control variables


  Variables that are kept the same in an experiment
• Key terms


  • Reliable
  • Accurate
  • Valid
  • Fair test
• Independent variable


  The variable that the scientist alters during an investigation
• Control experiment


  An experiment carried out to check the results of another experiment by removing the element/s under investigation
• Fair test


  Ensuring that everything else that could affect the results is kept the same
• Accuracy


  Getting results that are really close to the true answer. Use sensitive instruments, measure in small increments
• Reliability


  Repeat, repeat, repeat...
• Anomalous results


  Results that don't fit in with the rest. Either too high/low. Ignore when finding averages