1b 3cm³ 0.1% Glucose and 1cm³ Dilute Hydrochloric acid were pipetted into a boiling tube. The boiling tube was placed in the water bath until the solution had boiled for 2 minutes. The boiling tube was then removed and allowed to cool. The solution was then neutralised using Sodium Hydrogen Carbonate. Note: Enough of the Sodium Hydrogen Bicarbonate was used to stop the solution effervescing. Neutralisation was checked using Litmus paper. Another 5cm³ Benedict’s reagent was added and the boiling tube was replaced in the water bath for 8 minutes. The boiling tube was then removed, allowed to cool and the colour was noted.
1c 3cm³ 0.1% Glucose solution and a few drops of 10% sucrase enzyme were added together. The boiling tube was then left for two minutes but was shaken gently so that the enzyme was distributed evenly. 5cm³ Benedict’s reagent was then added. The boiling tube was placed in the water bath for 8 minutes, then removed and cooled. The colour was noted.
2a, b, c The above procedures were repeated except that 0.1% sucrose was used instead of 0.1% Glucose.
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 10cm³ of water, but only 3cm³ 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 10cm³ of water, but only 3cm³ was used.
Results
Conclusion
Glucose a monosaccharide is a reducing sugar as it formed a red precipitate with Benedict’s reagent. It could not be broken down any further therefore it remained a reducing sugar in procedure b and c. Sucrose is a disaccharide made up of glucose and fructose. As it can be broken down to these to monosaccharides it is not a reducing sugar and therefore did not form a red precipitate with Benedict’s reagent. The disaccharide broke down in procedure b and c to give a positive result for a reducing sugar because the hydrochloric acid is the acid in the stomach so it breaks substances down. Also sucrase is the enzyme for sucrose so it would have also broke down the disaccharide.
The unknown substance was not a monosaccharide as it did not produce a red precipitate when added to Benedict’s reagent. Yet again it was broken down by Hydrochloric acid and with sucrase. I therefore predict that the unknown is a disaccharide or a polysaccharide containing sucrose.
Grass also did contain some reducing sugars as when added to Benedict’s reagent it formed a green precipitate. 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 , especially cane sugar. Molasses contains uncrystallized sugar and some . 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.