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First teaching 2023

First exams 2025

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Testing for Non-Reducing Sugars (CIE AS Biology)

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Cara Head

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Cara Head

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Testing for Non-Reducing Sugars

  • Sugars can be classified as reducing or non-reducing; this classification is dependent on their ability to donate electrons (a reducing sugar that is able to donate electrons is itself oxidised)
    • OILRIG in Chemistry
  • If Benedict's test has been carried out on a solution and it shows that no reducing sugars are present then a modified version of the test can be carried out to test for the presence of non-reducing sugars

To test for non-reducing sugars:

  • Add dilute hydrochloric acid to the sample and heat in a water bath that has been brought to the boil
  • Neutralise the solution with sodium hydrogencarbonate
    • Use a suitable indicator (such as red litmus paper) to identify when the solution has been neutralised, and then add a little more sodium hydrogencarbonate as the conditions need to be slightly alkaline for the Benedict’s test to work
  • Then carry out Benedict’s test as normal; add Benedict’s reagent to the sample and heat in a water bath that has been boiled – if a colour change occurs (orange-red precipitate), a non-reducing sugar is present

Explanation

  • The addition of acid will hydrolyse any glycosidic bonds present in any carbohydrate molecules
  • The resulting monosaccharides left will have an aldehyde or ketone functional group that can donate electrons to copper (II) sulfate (reducing the copper), allowing a precipitate to form

Reducing & Non-reducing Sugars Table

Reducing Sugars Non-Reducing Sugars
Galactose Sucrose (the only one you need to know)
Glucose
Fructose
Maltose

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Cara Head

Author: Cara Head

Expertise: Biology

Cara graduated from the University of Exeter in 2005 with a degree in Biological Sciences. She has fifteen years of experience teaching the Sciences at KS3 to KS5, and Psychology at A-Level. Cara has taught in a range of secondary schools across the South West of England before joining the team at SME. Cara is passionate about Biology and creating resources that bring the subject alive and deepen students' understanding