Investigating and testing for reducing and non-reducing sugars
Biology - Experiment write up
Investigating and testing for reducing and non-reducing sugars
Aim: To use techniques to test a selection of known and unknown substances, to determine whether or not they are a reducing, non-reducing sugar or neither.
Prediction: In the first part of the experiment (simple Benedict's test), I predict that out of the three solution samples; glucose, sucrose and sample X, only glucose will change from the blue colour. I do not know what the substance in sample X is and therefore cannot comment on the outcome. However in my opinion sucrose will not change colour during this part of the experiment.
In the second part of the experiment, when using acid to break any glycosidic bonds and sodium hydrogen carbonate to neutralise the solution, I predict that sucrose will change colour. In my opinion the part of the experiment will make no difference to the glucose and therefore the outcome to this second part will be the same as part one of the experiment.
Apparatus List:
* Beaker
* Test tube rack
* Test tubes
* Samples of sugar solutions
* Syringe
* Pipette
* Benedict's solution
* Hot water available
* Hydrochloric acid, HCL
* Sodium hydrogen carbonate, NaHCO3
* Universal indicator paper
Theory: Benedict's solution is often 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 yellow-red precipitate. However, some saccharides need to be split and neutralised in order to detect their reducing sugars.
Redox Reaction
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* Test tubes
* Samples of sugar solutions
* Syringe
* Pipette
* Benedict's solution
* Hot water available
* Hydrochloric acid, HCL
* Sodium hydrogen carbonate, NaHCO3
* Universal indicator paper
Theory: Benedict's solution is often 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 yellow-red precipitate. However, some saccharides need to be split and neutralised in order to detect their reducing sugars.
Redox Reaction
Cu(( Cu((
Glucose is a monosaccharide. This means that the sugar solution is made up from many single sugar units that cannot be broken down into a simpler form. Monosaccharides are small, sweet, white, soluble and crystalline. Disaccharides are very similar, the are also small, sweet, white, soluble and crystalline. However, due to condensation reactions forming glycosidic bonds (due to the loss of water), disaccharides are formed from two monosaccharide units.
If the copper sulphate within the Benedict's solution is reduced it can be measured quantitively. The colour determines the amount of reducing sugar...
Blue Green Yellow Orange Red Browny
Method:
* Firstly I collected the apparatus that I would need for the experiment, using the syringe, I measured out, as accurately as possible 2ml of each sample of solution and put it into 3 separate test tubes.
* After, I placed the test tubes into the test tube rack and carefully boiled some water, which I then poured into the beaker.
* Using the pipette, I tried to put as equal as possible, amounts of Benedict's solution into each test tube. I then placed all of the tubes into the beaker of hot water and recorded any colour changes.
* As the glucose changed colour I know only needed to perform the second part of the experiment on the sucrose and X samples.
* I washed out the test tubes and again using the syringe measured out equal quantities of each solution, and placed the tubes back in the rack.
* Next, I measured out two amounts of 1ml of hydrochloric acid, HCL, using the syringe and put it into each test tube; giving it a small amount of time to break any glycosidic bonds.
* After, I added small amounts of sodium hydrogen carbonate, NaHCO3, in 0.5ml parts. In between each I used universal indicator paper to test whether the solutions were neutral (green). I continued until each solution was neutral.
* Finally, I re-boiled the kettle and re-filled the beaker with the water (the hotter the better). I then put as equal as possible, amounts of Benedict's solution into each test tube and placed them into the beaker with the hot water. I finished by recording the colour changes.
Results:
Sample
st part of experiment
Colour change
2nd part of experiment
Colour change
Type of sugar
X
No change
No change
Not a sugar
Glucose
Blue to Orangey red
n/a
Reducing sugar
Sucrose
No change
Blue to orange
Non-reducing sugar
Conclusion: In conclusion, from the experiment I carried out and the results that I collected I can see that glucose reduced the copper (II) ion straight away with simply testing with Benedict's solution only. The glucose is therefore a reducing sugar, as the colour of the blue copper sulphate changed to an Orangey red without the sample's bonds needing to be broken down.
Sucrose on the other hand, did not reduce the copper sulphate in the first part of the experiment as the colour of the solution did not change at all. I could therefore tell that the sample sugar, sucrose was not a reducing sugar. After completing the second part of the experiment the colour changed. This means that sucrose is a non-reducing sugar.
Solution X unlike the other two samples showed no colour change in either experiment. This therefore means that this sample is not a sugar.
To improve this investigation I would repeat the experiment another two times, to ensure accurate results. I could also use a more accurate to measure the quantities of the liquids used. For example, by using a liquid level sensor.
