Investigation to determine the affects of different concentrations of sugar on benedict’s solution.

Results:

Concentration of sugar solution (%)

Colour of solution after heating with Benedict's for 3 minutes

0

Copper

Red

0.1

Orange

0.01

Turquoise

0.001

No apparent change

Analysis: From the results it is clear to see that the more concentrated the sugar solution, the more intense the end colour. In this reaction glucose acts as a reducing agent and the coloured precipitates are due to the formation of copper(I) oxide from the copper sulphate in the benedicts solution. The intensity of this precipitate is dependant upon the concentration of the sugar solution. When the solution is very concentrated, there are more sugar molecules to reduce the copper sulphate. This means that more copper oxide will be produced. This insoluble copper oxide makes the colour of the solution change. The more copper oxide there is, the more intense the precipitate. When the concentration of the sugar solution was 10%, the precipitate was an intense copper. However when the concentration was 0.001% there was not enough sugar molecules to reduce the copper sulphate, therefore there was no apparent colour change.

Evaluation: There were several sources of error in this experiment which would lead to inaccuracies in the results. The first of these is the cross contamination of the different concentrations of sugar solution. The syringes that were used were not reliable because the syringe did not have a plunger that was completely intact. This meant that traces of the previous concentration were still in the syringe. This would mean that the concentration of sugar in each test tube was not the concentration that was intended. An improvement to the experimental method would be to use a new test tube for each extraction of sugar solution. A water bath was used to ensure an even distribution of heat to the 5 test tubes. This ensures a fair test. Also the water bath guaranteed that the 5 test tubes stayed stationary. If the test tubes were shaken during the 3 minutes it may have had an effect on the experiment. However the use of a water bath has some negative drawbacks. The 5 test tubes were placed in the water bath one after another. This means that there was a short time lapse between each going in. This time lapse means that the 5 test tubes were not in the water bath for an equal amount of time. Equally this problem occurred when the test tubes were removed. A way of preventing this would be to use a water bath that could accommodate a test tube rack so that the tubes could be placed and removed from the water at the same time.

The 5 different colours that were made can be used to approximately measure the concentration of any unknown sugar solution. The next experiment tests this theory.

Method: Three sugar solutions (A,B,C) of unknown concentration were provided. A 9cm3 sample of each was placed in three different test tubes. 5 cm3 of benedicts solution was added to each test tube. This made the total volume of solution in each of the test tubes match that of the first experiment, this makes it a fair test. The three test tubes were placed in a water bath filled with boiling water for 3 minutes, much like the first experiment. The results after 3 minutes were recorded.

Results:

Solution with unknown concentration

Colour after heating with benedicts for 3 mins

Approximate concentration

(%)

A

Orange

0.1

B

Red

C

Turquoise

0.01

Analysis: Each of the three test tubes were compared with the precipitates created from the first experiment. From this it was possible to deduce the approximate concentration of each solution. Solution A went orange, this coincided with the 0.1% concentration from the previous experiment. Solution B went red, this matched the 1% concentration. And solution B went turquoise, this resembled the 0.01% concentration.

Evaluation: The most major source of error in this experiment was the colour inaccuracies. The colour matches were only one persons perception of the colour. Another person may match the colours differently as their perception is different. The copper oxide that is formed is insoluble and therefore will settle over time. This means that the colours from the first experiment would have faded by the time the second experiment had finished as the copper oxide would have separated from the rest of the solution. To prevent this source of error the precipitates from the first experiment should have been stirred or shaken so that the copper oxide was evenly distributed throughout the solution. This would make the colours more accurate.