Apparatus
The equipment that will be used for the experiment include,
- test tubes, which will contain solutions, I.e. the juices,
- test tube rack
- a syringe, to measure the quantity of solution going in.
- water bath, the solutions are heated in the bath water.
The solutions used in this experiment will be, 4% glucose solution, distilled water, benedict’s solution and finally fresh orange, lemons and grapefruit.
Method
1. Firstly take four test tubes and label them so that it will be possible to identify one solution from another.
2. Using a syringe transfer 4% of glucose and put it in the first test tube.
3. 4% of each of the fruit juice must also be put into the test tubes,
4% glucose
1g in 100cm3
So 4g in 100cm3
1000mg = 1g
4000mg in 100cm3
Therefore we need 40mg of juice per 1cm3
Do all calculations in mgcm-3 (not in %)
4. Add 9cm3 of distilled water to each of the four test tubes.
5. Add 5cm3 benedict’s solution in each tube.
6. Place all four test tubes in water bath and leave for 9 minutes.
7. Remove all the tubes from the water bath and return them to the test tube rack to compare the colours of the 3 juices to the glucose solution and compare against each other.
Variables
In order for it to be a fair test the measurements of everything in the experiment need to remain the same. The temperature at which the solutions should be heated at 75 degrees, and left in for exactly 9 minutes. These are all the factors that we can control, the variables will of course be the different sugars which we are testing for the amount of glucose. Although the sample in themselves will be different the amount should remain the same so that it will be a fair test.
The reason why we conduct a fair test is so that the results we get at the end of it will be reliable and so that we will be able to analyse the results confidently and make accurate predictions for future experiments.
From preliminary experiments, it is possible to rely on the factors that we will control and know that the volume of solution, the temperature, etc.. is suitable for the experiment we are planning to undergo.
Whilst conducting an experiment it is important to consider the risks and safety precautions, for example to wear safety goggles, and a lab coat etc.. This is to ensure we always remain safe throughout the experiment.
Preliminary Experiments
It is always best to conduct a preliminary experiment in order to know whether or not you have a suitable range of values, etc… That is why we had done quite a few experiments in lessons, below are the results.
The experiment we did was to investigate the sensitivity of the benedict’s test. There were three parts to this, the first was to make a serial dilution of glucose solution, below are the results:
From the results you are able to depict that the benedict’s solution is quite sensitive and therefore reliable as it was able to detect glucose at 0.1%.
The second part of the experiment was to test for glucose from ‘unknown’ solutions, below are the results:
From the results we can see that test tube A clearly contained glucose, test tube B did not. As for the lemon juice the colour before was very pale, as it had been diluted , however the benedict’s solution did turn the yellow that it was very dark. This will have to be taken into consideration as we are working with three fruit juices, therefore from these results we can only assume that they will remain the same colour, or similar.
The final experiment that we did was to use a colorimeter to test for glucose in a solution, below are the results:
The results show that the more glucose there was the more it reduced the copper ions, which is why less light was absorbed as the concentration of glucose was higher. From these results you are able to draw a calibration curve, which could then be used to find out the concentrations of unknown solutions by simply reading of the values on the curve.
Outline
From looking at the preliminary experiments we are able to see that the results were of high-quality and therefore we can feel confident that the following experiment we are about to perform will be a success and give us an accurate set of results. Out of all three of the experiments done the final one was probably most accurate as a colorimeter was used which means we will also be using a colorimeter in the experiment to take place.
From looking at the preliminary experiments I am certain that I will not change any of the variables, or the method. Therefore I will carry on as normal, as a result my prediction remains the same. I believe all of the solutions will contain reducing sugars, hence turn the solution a red colour. The solution will reduce the benedict’s solution because it is a monosaccharide, which are single sugar units. Sugars are able to reduce a benedict’s solution when the anomeric carbon atom is made available to reduce the copper ions in the solution. The best way to test my prediction now, is to carry out my experiment.