CIE IGCSE Biology: 复习笔记:4.1.2 Food Tests

CIE IGCSE Biology: 复习笔记:4.1.2 Food Tests

Food Tests

Test for glucose (a reducing sugar)

  • Add Benedict's solution into sample solution in test tube
  • Heat at 60 - 70 °c in water bath for 5 minutes
  • Take test tube out of water bath and observe the colour
  • A positive test will show a colour change from blue to orange or brick red

The Benedict's test for glucose

 

 Test for starch using iodine

  • We can use iodine to test for the presence or absence of starch in a food sample.

The iodine test for starch

  • Add drops of iodine solution to the food sample
  • A positive test will show a colour change from orange-brown to blue-black

Testing a potato to prove the presence of starch

Test for protein

  • Add drops of Biuret solution to the food sample
  • A positive test will show a colour change from blue to violet / purple

The Biuret test for protein

Test for lipids

  • Food sample is mixed with 2cm3 of ethanol and shaken
  • The ethanol is added to an equal volume of cold water
  • A positive test will show a cloudy emulsion formingThe ethanol test for lipids

Test for vitamin C

  • Add 1cm3 of DCPIP solution to a test tube
  • Add a small amount of food sample (as a solution)
  • A positive test will show the blue colour of the dye disappearing

The DCPIP test for vitamin C

Exam Tip

When describing food tests in exam answers, make sure you give the starting colour of the solution and the colour it changes to for a positive result.

转载自savemyexams

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