Tests for sugars & starch

• What types of sugars are reducing sugars?

  All monosaccharides and some disaccharides like maltose and lactose.
• What types of sugars are non-reducing sugars?

  sucrose.
• What reagent is used to test for reducing sugars?

  Benedict's reagent.
• What colour is Benedict's reagent?

  blue.
• What indicates a positive result in the test for reducing sugars?

  A brick red precipitate forms.
• What indicates a negative result in the test for reducing sugars?

  The solution remains blue.
• How can the amount of reducing sugar be measured quantitatively?

  By filtering the solution and weighing the precipitate.
• What tool can be used to measure the absorbance of Benedict's solution?

  A colorimeter.
• What reagent is used to test for starch?

  Iodine.
• What is a positive result when testing for starch?

  The iodine will turn from brown/yellow to blue/black.
• Is the starch test qualitative or quantitative?

  Qualitative.
• How can the amount of precipitate in a reducing sugar test be measured quantitatively?

  By filtering the solution and weighing the precipitate.
• Describe the test for a reducing sugar.

  • Add benedict's reagent to the sample
  • Heat in a water bath
  • Positive result: Blue to brick red precipitate
• Describe the test for a non-reducing sugar.

  1. Following a negative reducing sugars test
  2. Boil sample in acid. Then add alkaline solution to neutralise.
  3. Add benedict's and heat
  4. Positive result: Blue to brick red precipitate
• Describe the test for starch.

  • Add iodine to the sample
  • Positive result: Orange to blue black