CLAPSTONE LEARNING

Is the Benedict's Test for reducing sugars qualitative or quantitative? The test may be qualitative, or it may be quantitative. The  qualitative  test produces a colour change from blue to green to yellow to orange to brick red.  The qualitative test is also regarded as  semi-quantitative  as the colour obtained correlates to the concentration of reducing sugars in the solution ( see observations below). This allows for a rough estimation of the amount of reducing sugar present.  The  qualitative test is discussed here . The  quantitative  test involves the use of potassium thicyanate and the production of  copper thiocyanate  as white or pale green precipitate. This precipitate can then be titrated. PROCEDURE What is the procedure for the Benedict's Test for reducing sugars? A  liquid food sample  does not need prior preparation except dilution if viscous or concentrated. For a  solid sample  prepare a test solution by crushing the food and adding a moderate am

De-starching the Leaves of a Plant 'De-starch (or Destarch) the leaves of a potted plant' is one of the preliminary steps in a  photosynthesis experiment . Biology students often ask the following questions about de-starching. What is  the definition of de-starching? Why it is necessary to de-starch the leaves of a plant before conducting photosynthesis experiments? What happens to the starch stores when the potted plant is deprived of light or carbon dioxide? How to de-starch the leaves of a plant? What is the definition of de-starching? De-starching is the process by which the starch reserves in a plant are depleted by depriving the plant of either light or carbon dioxide.  Why is it necessary to de-starch the leaves of a plant before conducting photosynthesis experiments? We test for the presence  of starch  in leaves in order to determine that photosynthesis has occurred. Glucose -  the product of photosynthe

Ethanol Emulsion Test for Fats and Oils The  Ethanol Emulsion Test  is a  food test  which determines the presence of a broad group of naturally occurring compounds known as  lipids . Lipids consist of  fats  and  oils . Other lipid tests include the  Grease Spot Test  and the  Sudan Stain Test . The Grease spot test is performed on fats - lipids which are solid at room temperature. Sudan stain colours lipids red, but is a less common bench reagent than ethanol. The Ethanol Emulsion Test is the most common test amongst the three. Procedure Solid sample  Crush  the food sample and place in a dry test tube. Add ethanol  to about 2 cm3 above the level of the sample and shake thoroughly. Allow the solid to  settle  (about 3 min) to allow the lipid to be extracted. Decant  the ethanol into another test tube. Add 2 cm3 of  deionized water  to the second test tube Make observations. Liquid sample Add a  few drops  of the liquid food sample to a dry te

What is Benedict's Test for Reducing Sugars? Benedict's Test for non-reducing Sugars  is a test which determines the presence of  non-reducing sugars  in a test solution. The principal reagent in Benedict's Test for Reducing Sugars is Benedict's Solution which contains copper(II) sulphate sodium carbonate sodium citrate What are reducing sugars? Sugars are classified as  reducing  or  non-reducing  based on their ability to act as a reducing agent during the Benedict's Test. A reducing agent donates electrons during a redox reaction and is itself oxidized. The  aldehyde functional group  is the reducing agent in reducing sugars. Reducing sugars have either an aldehyde functional group or have a ketone group - in an open chain form - which can be converted into an aldehyde. Reducing sugars are  simple sugars  and include all monosaccharides and most disaccarides. Some examples of monosaccharides are glucose, fructose and

The  Iodine Test for Starch  is used to determine the presence of starch in biological materials. The test can be qualitative or quantitative. As a Biology Student, you will be testing for the presence of this  complex carbohydrate in foods  or in leaves as part of a  photosynthesis experiment. These are qualitative tests. If you study chemistry as well, you should pay attention principle of the test, as it helps explain how starch acts as an  indicator for Redox Titrations  or in the  ' Iodine Clock Reaction '.   These extensions of the Iodine Test for starch yield qualitative results. The sole reagent required for the test is  bench iodine solution   (0.1 M potassium triiodide solution). PROCEDURE What is the procedure for the iodine test for starch? The procedure  for the iodine test for starch depends on whether the test sample is a solid or liquid. SOLID SAMPLE Peel  off the skin of any vegetables e.g. potato and fruits as these are oft