My aim is to design an experiment to compare quantitatively orange fruit, grapefruit and lemon fruit, with respect to the amount of glucose they contain. I will endeavour to make the experiment as fair as possible and aim to minimise the amount of errors.

Prediction:

I predict that orange juice is the most concentrated out of the three juices, which are orange, grapefruit and lemon. Orange juice should have a higher concentration of glucose, followed by Grapefruit then lemon. I have predicted this because of a source I have obtained which showed that orange has the greatest number of grams of monosaccharides.

(Manuel of nutrition by Mafa)

If there is a greater number of monosaccharides there would be a higher concentration of glucose present. Benedict’s test can prove this as the more reducing sugar present the greater the amount and the darker the colour of the precipitate.

A Benedict’s test is a test, which can be used to show the presence of reducing sugars.

I predict that orange juice would have the a more red precipitate colour solution followed by grapefruit with a slight brownish yellow precipitate, then will be lemon juice with the lightest colours of these precipitate.

I predict that the orange juice will form a more reddish colour then the grapefruit or the lemon juice, this is based on the amounts of monosaccharides in grams shown above.

Fair test:

• I will be keeping the temperature constant
• All test tubes will be equal in size
• The cuvettes will be rinsed out after use with the next solution.
• The amount of time that the test tubes will lay in the water bath will be constant.

Factors and Variables:

 

Health and Safety:

Although this experiment is not extremely hazardous safety procedures must still be taken. Safety is very important and it is necessary to follow safety procedures when doing any experiment. Long hair and objects must be tied back. A lab coat should be worn in case any spillage falls onto your clothes.

To avoid any accidents the apparatus should be set up correctly, it should also be set up in a suitable place such as the middle of the lab table.

The solutions should be labelled correctly and the lids of the solutions should are placed on the right bottles and should be secured tightly on

The water bath is set at a very high temperature so caution must be taken to avoid any accidents from occurring. Removing and placing anything from the water bath must be taken very seriously and with great care, this will prevent any burns and scaling.

Apparatus

• 4% glucose solution
• Colorimeter,
• cuvettes,
• Water bath,
• Test tube rack,
• Test tube,
• Distilled water.
• 10ml graduated pipette
• 25 ml of Benedict’s solution
• Water Bath
• Coloured pencil
• Thermometer
• Juices, apple, orange, grapefruit.

Choice Of Apparatus

Method:

• Label the six clean test tubes 1-6, do this by encrypting the top of the test tube with a coloured pencil.
• Use the pipette to remove 10mls of 4% glucose solution and insert it into test tube numbered 1. Make sure the solutions meniscus is lying on the line of the measured amount in the pipette.
• Using the pipette remove 5ml of the 4% glucose from test tube 1 into test tube 2 by using a clean pipette.
• Add 5 ml of distilled water to test tube 2, by using a clean pipette, test tube to should contain a 10ml of the solution. Glucose solution should now be 2%
• From test tube 2 remove 2.5ml of glucose/distilled water solution and insert it to test tube 3, add 7.25ml of distilled water to that, which will all equal 10ml. Glucose solution should now be 1%
• From test tube 3, remove 1.25ml of the glucose/distilled water solution with the pipette and add it to test tube 4, insert 8.75ml of distilled water. Glucose solution should now be 0.5%
• From test tube 4 remove 0.625ml of the glucose/distilled water solution into test tube 5 and add 9.375ml of distilled water. Glucose solution should now be 0.25%
• From test tube 5 remove 0.31ml of the glucose/distilled water solution into test tube 6 and add 4.69 of distilled water. Then add 5 ml of either juice such as the orange juice, lemon juice or grapefruit juice, by measuring it in a new and clean pipette and place it into test tube 6.
• Add 4ml of benedict’s solution into all 6 test tubes.
• Place the test tube rack, which contains test tubes in the water bath, which should be set at 100oC, for 5 minutes.
• Remove the test tube rack simultaneously and place the solution of each test tube, starting from test tube 1 into a cuvette, this should be ¾ full to avoid any spillage.
• Shake and the solutions in each test tube considerably.  
• Rinse out the cuvettes after each reading by placing some of the next tubes solution; pour that down the sink and record the next reading with the solution.
• Record all the colour transmissions.
• Repeat each experiment at least three times.
• Carry out the same experiment for the remaining juices.

Reducing Errors

Accuracy is very important in this experiment. This means that as many measures as possible need to be taken, to make the results as accurate as possible. It is very important to use the most appropriate equipment available for use. This is why I have chosen to use a pipette, as this has an accuracy of +-0.005 cm, which should produce a suitable accuracy for my experiment. It is very important to read of the pipette as accurately as possible and to make sure that the reading is taken from the bottom of the meniscus. It will be necessary to make sure the equipment is clean to get concordant results. Some of the equipment will need to be washed out with a particular solution. For instance when washing out the cuvette you must wash it out with the solution that you will be using next, as if you washed it out with the distilled water this would effect the dilution concentration and therefore would affect the results.

Table Of Results

Apple Juice

Grapefruit Juice

Orange Juice