2.1.5 - Biochemical tests for molecules

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Benedicts test for sugars: 

  • Reducing- Reducing sugars include all monosaccharides and some disaccharides. You add benedicts reagent (coper sulphate) to a sample and heat it, making sure the solution doesn't boil. If the test is positive, it will form a coloured precipitate (solid particles suspended in water). It will eventually turn brick red. The higher the concentration of reducing sugar, the further the colour change goes- you can use this to compare the amount of reducing sugar in different solutions. A more accurate way of doing this is to filter the solution and weigh the precipitate
  • Non-reducing, e.g. sucrose- To test for them, first you have to break them down into monosaccharides. You do this by boiling the test solution with dilute hydrochloric acid and then neutralising it with sodium hydrogencarbonate. Then just carry out the benedicts test as you would for a reducing sugar. If the result of this test of positive, the sugar could still be reducing or non-reducing. To check its non-reducing you need to do the reducing sugar test (to rule it

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