sugars

• all carbohydrates contain the elements C, H, O - monomers of carbohydrates are made from monosaccharides e.g. glucose, fructose and galactose
• glucose is a hexose sugar - monosaccharide with 6 carbon atoms in each molecule
• 2 types of glucose:

  • alpha
  • beta
  • they are isomers - molecules with the same molecular formula as each other but with atoms connected in different way
• disaccharide formation - disaccharide is formed when 2 monosaccharides join together by condensation reactions - glycosidic bond forms between 2 monosaccharides as a molecule of water is released
• sucrose = glucose + fructose
• lactose = glucose + galactose
• The Benedict's test:

  • all sugars can be classified as reducing sugars or non-reducing sugars
  • to test for sugars use Benedict's
  • test differs depending on what type of sugar you are testing for
• Reducing sugars:

  • include all monosaccharides and some disaccharides e.g. maltose and lactose
  • add Benedict's reagent to a sample and heat in a water bath that has been brought to the boil
• positive - coloured ppt - solid particles suspended in the solution

  colour of ppt changes

  • green-yellow-orange-brick red
• higher the concentration of the reducing sugar - further the colour change goes - can use to compare amount of reducing sugar in different solutions
• more accurate way of doing this is to filter the solution and weigh the precipitate or remove the ppt and use a colorimeter to measure absorbance of remaining Benedict's reagent