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Investigating and testing for reducing and non-reducing sugars

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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. ...read more.


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. ...read more.


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. ?? ?? ?? ?? ...read more.

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3 star(s)

An adequate report of an investigation into the identities of three food samples. The writer has correctly described the appropriate sugar tests and draws relevant conclusions. However, to fully satisfy 'A' level requirements, the report needs to describe the methods used in more detail with special attention to volumes, times and temperatures. It would have been helpful if the writer had given details of the chemistry behind the Benedict's test (donation of electrons, etc.) and exactly why glucose is - and sucrose is not - a reducing sugar.

3 stars

Marked by teacher Ross Robertson 19/06/2013

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