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Aim: To test for reducing sugars using glucose, sucrose and lactose to see which one can be reduced.

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  • Essay length: 619 words
  • Submitted: 17/10/2006
  • Marked by teacher: (?) Adam Roberts
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Teacher essay summary

3 star(s)

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

The first 200 words of this essay...

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. The original pale blue colour means no reducing sugar, a green precipitate means relatively little sugar; a brown or red precipitate means progressively more sugar is present.

Non-reducing Sugars (Benedict's test). Sucrose is called a non-reducing sugar because it does not reduce copper sulphate, so there is no direct test for sucrose. However, if it is first hydrolysed (broken down) to its constituent monosaccharides (glucose and fructose), it will then give a positive Benedict's test. So sucrose is the only sugar that will give a negative Benedict's test

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MbT essay summary

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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