Aim: To test for reducing sugars using glucose, sucrose and lactose to see which one can be reduced.
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Reducing and non-reducing sugars and the Test Reducing Sugars (Benedict's test). All monosaccharide and most disaccharides (except sucrose) will reduce copper (II) sulphate, producing a precipitate of copper (I) oxide on heating, so they are called reducing sugars. Benedict's reagent is an aqueous solution of copper (II) sulphate, sodium carbonate and sodium citrate. To approximately 2 cm³ of test solution add an equal quantity of Benedict's reagent. Shake, and heat for a few minutes at 95°C in a water bath. A precipitate indicates reducing sugar. The colour and density of the precipitate gives an indication of the amount of reducing sugar present, so this test is semi-quantitative.
Neutralise the solution by gently adding small amounts of solid sodium hydrogen carbonate until it stops fizzing, then test as before for reducing sugars. Examples of Disaccharides Sucrose: glucose + fructose, Lactose: glucose + galactose, Maltose: glucose + glucose. Maltose: glucose + glucose. Sucrose is used in many plants for transporting food reserves, often from the leaves to other parts of the plant. Lactose is the sugar found in the milk of mammals and maltose is the first product of starch digestion and is further broken down to glucose before absorption in the human gut. Aim: To test for reducing sugars using glucose, sucrose and lactose to see which one can be reduced.
in to copper (Cu2O), which makes it turn in to a red brown precipitate. As a result the aldehyde group is oxidised the carboxyl group. I used Benedict's reagent to test for reducing sugar, benedict's regent used to test for monosaccharides e.g. glucose and fructose. Benedict's reagent contains blue copper (II) sulphate (CuSO4), which is reduced to red copper (I) oxide by aldehyde thereby oxidising the aldehyde to carboxylic acids. I have discovered that sugars what are in the aldehyde group can either be oxidised or reduced by the benedict's reagent, that is why glucose and lactose where changed colour and sucrose didn't.
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Here's what a teacher thought of this essay
A fairly good summary of the test method and reasons why some sugars are reducing and others not, but the chemical explanations are a little superficial and unclear in places.
Marked by teacher Adam Roberts 11/04/2013
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