4) Using firstly 1cm3 of the solution from tube 2, go on to prepare three more glucose solutions systematically: 0.1% (tube 4) and 0.001% (tube 5).
5) Finally, adjust so that all five tubes contain an equal volume of liquid.
6) Using the syringe add 5cm3 of Benedict’s solution to each tube.
7) Transfer all five tubes to the boiling water bath provided for exactly three minutes.
8) Remove and return to the rack.
9) Make a subjective comparison of the colours in each tube by observation. You can use a scale of ‘+’ to ‘+++++’ to record the depth of colour, from lightest to darkest.
10) Use the colorimeter to measure the percentage transmission of each of your samples.
11) Tabulate all your readings and present them in a suitable graph.
Table of results
Graph
Conclusion
From this table you can see that the 10% glucose solution had the darkest colour dark orange after testing for reducing sugars whereas the 0.001% glucose solution remained blue. This suggests that as the percentage of glucose was increased the darker the colour became meaning that there was more glucose present.
From the graph of average percentage transmissions of glucose in each sample, we can see that the graph has formed a smooth curve indicating as the concentration of the glucose increases so does the percentage transmission of the colour. The results of the experiment did show the correct results as predicted. However, there was an anomaly in the results. In group three after testing the percentage transmission of glucose sample 0.01% using a colorimeter, the result was 0.07. After testing this for the 0.001% glucose sample, the result was 0.08. This was not supposed to happen and in actual fact the 0.01% sample of glucose should have had a higher percentage transmission than the 0.001% sample of glucose not the other way round. This suggests that, there was an error in the experiment. This may have occurred because of a reading error on the colorimeter or it may have been because the glucose samples had been mixed up (s explained in the evaluation).
Evaluation
I believe the experiment was accurate as the same volume of liquid was used in each sample. This was also true for the benedict’s solution. Therefore, it was a fair test. However, it was not a complete fair test as the experiment was only carried out once, therefore the results lacked reliability. To make this experiment more accurate we should carry it out at least three times, so the results can be compared.
There were many small errors that occurred throughout the experiment affecting its results. Firstly when measuring the distilled water there may have been inaccuracy reading the measuring cylinder posing inaccurate results. Also, when we were using the pipette to put the 10% of glucose solution into the boiling tube and transferring a sample into other boiling tubes there were air bubbles in it, so the amount of glucose may not have been accurate. Therefore, there may have been different volumes of liquid in each boiling tube.
Another problem aroused by the anomaly of the experiment as described in the conclusion. This could have occurred because when we put the samples of glucose into cuvettes after heating them with benedict’s solution present in them the two end samples of 0.01% and 0.001% were similar colour. As some groups, when putting them in the colorimeter may not have labelled the cuvettes, they may have been mixed up producing these results. There was also the problem of the percentage transmissions on the colorimeter fluctuating, therefore there were two or three readings, and so a 100% accurate reading was not taken.
Finally another problem was time keeping. When we placed the boiling tubes in the boiling water bath it was impossible to put them all in at the same time and the same situation occurred when taking them out. Therefore, the time when each boiling tube went in and came out was different, maybe causing some glucose samples having more time to change colour.
This test was quantitative as we measured the cloudiness (turbidity) of the solution using a colorimeter. To extend this investigation making it quantitative we could also filter and weigh the precipitate produced. This would give us an indication of the measurement of the amount of sugar present in the sample.
Risk assessment
-Make sure a lab coat is worn, so that if any chemicals spill on you, they will not ruin your clothes and even more importantly will not harm you, or irritate your skin.
-If a substance touches your hands or skin, wash it immediately as it may be irritant or corrosive in turn harming your skin. If it does irritate tell you teacher.
-Be careful of fragile equipment, especially glass. Keep equipment away from the edge of surfaces to prevent glass from breaking and any chemicals from spilling.
-Tuck in stool underneath tables and make sure bags and coats are hung up so pupils do not trip up or get hurt.
-Follow instructions carefully and if you are not sure ask the teacher to help you to prevent you from doing anything wrong.
-Be careful of the boiling water bath, as it will be hot. Do not directly put your finger in there, as it will burn them.
-Tidy away equipment making sure used equipment is not mixed in with clean equipment, as this will affect other pupil’s results when they carry out the experiment.