Sugars

• All carbohydrates contain the elements C, H, O. The monomers that carbohydrates are made from are monosaccharides e.g. glucose, fructose and galactose
• • Glucose is a hexose sugar - a monosaccharide with six carbon atoms in each molecule
  • There are two types of glucose, alpha and beta glucose - theyre isomers (molecules with the same molecular formula as eachother, but with the atoms connected in a different way)
• A disaccharide is formed when two monosaccharides join together

  Monosaccharides are joined together by condensation reactions - a glycosidic bond forms between the two monosaccharides as a molecule of water is released
• • Sucrose is a disaccharide formed by a condensation reaction between a glucose molecule and a fructose molecule
  • Lactose is another disaccharide, formed from a glucose molecule and a galactose molecule
• Two alpha glucose molecules are joined together by a glycosidic bond to form maltose
• All sugars can be classified as reducing sugars or non-reducing sugars

  To test for sugars you use the Benedict's test

  The test differs depending on the type of sugar you're testing for
• Reducing sugars

  • Reducing sugars include all monosaccharides and some disaccharides e.g maltose and lactose
  • You add Benedict's reagent (which is blue) to a sample and heat it in a water bath that's been brought to the boil
  • If the test is positive it will form a coloured precipitate - brick red = reducing sugar present
  • The higher the concentration of sugar the further the colour change goes - you can use this to compare the amount of sugar in different solutions
  • A more accurate way of doing this is to filter the solution and weigh the percipitate or remove the precipitate and use a colorimeter to measure absorbance of the remaining benedicts reagent
• Non-reducing sugars

  • If the result of the reducing sugars is negative, there could still be a non-reducing sugar present
  • To test for non-reducing sugars, like sucrose, first you have to break them down into monosaccharides
  • You do this by getting a new sample of the test solution, adding dilute hydrochloric acid and carefully heating it in a water bath that's been brought to the boil
  • Finally just carry out the Benedicts test as you would for a reducing sugar