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An Experiment Testing for Carbohydrates Non-Reducing sugars

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Introduction

An Experiment Testing for Carbohydrates Non-Reducing sugars 28 September 2001 Aim To test for non-reducing sugars in 4 known substances and 1 unknown substance using Benedict's reagent and Hydrochloric acid neutralised with Sodium Hydrogen Carbonate. Introduction Benedict's test uses copper (II) sulphate. This reagent is used as a general test for detecting reducing sugars. If the saccharide is a reducing sugar, it will reduce the copper (II) ions to copper (I) oxide, and form a red precipitate. However, some saccharides need to be split and neutralised in order to detect their reducing sugars. Risks Hydrochloric acid is very poisonous and corrosive if spilt wash affected area immediately. Apparatus and Materials Boiling tubes x 15, Pestle and mortar, Water bath, Stop clock, Permanent Marker, 8 pipettes 10cm�, 9cm� 0.1% Glucose, 9cm� 0.1% Sucrose, 9cm� Unknown solution, 1g Grass, 1g Molasses, Litmus Paper, 20cm� Water, 3cm� Dilute Hydrochloric acid, 75cm� Benedict's Reagent, 9 drops Sucrase enzyme. Method The following tubes were prepared and labelled 1a 3cm� 0.1% Glucose and 5cm� Benedict's reagent were pipetted into a boiling tube. The boiling tube was placed in a water bath for 8 minutes. They were then removed and cooled. ...read more.

Middle

3a, b, c The above procedures were repeated except that the sample labelled unknown was used instead of 0.1% Glucose or 0.1% sucrose. 4a, b, c The above procedures were repeated except that grass was used instead of 0.1% Glucose, 0.1% sucrose or the sample labelled unknown. The grass was not in solution so 1g of the grass was grinded with 10cm� of water, but only 3cm� was used. 5a, b, c The above procedures were repeated except that molasses was used instead of 0.1% Glucose, 0.1% sucrose, the sample labelled unknown or grass. The molasses was not in solution so 1g molasses was grinded with 10cm� of water, but only 3cm� was used. Results Substance Procedure a Substance + Benedict's Procedure b Substance + Acid � Neutralisation + Benedict's Procedure c Substance + Sucrase + Benedict's 0.1 % Glucose RED - Yes RED - Yes RED - Yes 0.1% Sucrose BLUE - No RED - Yes BLUE - No Unknown BLUE - No RED - Yes RED - Yes Grass Clear GREEN - No RED - Yes RED - Yes Molasses ORANGE - Yes BLUE - No ORANGE - Yes Conclusion Glucose a monosaccharide is a reducing sugar as it formed a red precipitate with Benedict's reagent. ...read more.

Conclusion

Although this was hard to see due to the chlorophyll. However the grass had to be broken down by the hydrochloric acid before a red precipitate was formed. Procedure c has shown that grass does contain some sucrose as a red precipitate was formed when sucrase was added. Molasses, also called treacle, dark brown viscous liquid obtained as a by-product in the processing of [1]sugar, especially cane sugar. Molasses contains uncrystallized sugar and some [2]sucrose. Therefore, molasses contained some monosaccharides that is why an orange precipitate was formed when Benedict's reagent was added. Regular molasses (treacle) is an inverted sugar produced from the residue of refinement. Dark brown sugar has more colour and a stronger molasses flavour than light brown sugar. The acid treatment darkens it. Molasses is filtered and may have a sulphur compound added to sterilize and stabilize it. Therefore in procedure b the intensity of the molasses was increased. It would not have been broken down to produce reducing sugars. Another suggestion is that as the molasses is stabilized it will be very hard to breakdown so maybe a stronger form of Hydrochloric acid needs to be used. However in procedure c there was an orange precipitate after Benedict's reagent was used. So molasses also contain some sucrose. ...read more.

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