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You are required to plan a procedure that will allow you to compare quantitatively the glucose concentrations in samples of fresh orange, lemon and grapefruit.

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Introduction

You are required to plan a procedure that will allow you to compare quantitatively the glucose concentrations in samples of fresh orange, lemon and grapefruit. I predict that orange juice is the most concentrated out of the three juices. 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 monosaccharide. The juice sample The amount of monosaccharide in grams (g) Orange 8.5 Grapefruit 5.3 Lemon 1.6 ("Manuel of Nutrition" by J. 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. To prove my prediction I will require quantitative results, this can be done by carrying out an colorimetry experiment The experiment that I am planning involves the use of a Food Test for Reducing Sugars. This test is done by mixing an equal volume of Benedicts solution, to the test solution. It is then heated in a water bath for approximately 2 minutes 30 seconds. ...read more.

Middle

To give absorbance readings for samples Most Suitable method of getting accurate, absorbance readings Cuvettes (1) Used to put substances into, to put into colorimeter Standard apparatus used with the colorimeter Distilled water (1 bottle) To dilute solutions N/A Graduated pipette 10ml (1) To measure solutions accurately Most accurate and most suitable choice of measuring the solutions Test tubes (8) To place solutions into N/A Test tube rack (1) To hold test tubes Sole purpose of test tube racks are to hold test tubes Hot water bath (1) Maintain a chosen temperature This heats up the test tubes containing the solutions for reactions to occur Chinagraph pencil (1) To label the test tubes for us to recognise each test tube of different concentrations Can write on glass and can withstand heat so it won't rub off Coloured pencils (Range of different colours) To express different colours To record results given from the test tubes once they have come out the water bath. Most suitable way to express results effectively Benedicts Solution (1 bottle) Needed in the process for testing glucose N/A Glass rod (1) Used to stir the solutions. N/A 4% Glucose solution (1 bottle) Used to create solutions N/A 1. Using the chinagraph pencil, label the test tubes 1-5 near the top of the first 5 test tubes. On the remaining three, label them with lemon, grapefruit and orange. 2. Using the graduated pipette, pipette 8mls of 4% glucose solution into test tube 1. This should then be labelled '4%'. 3. Remove 4ml of the 4% glucose solution from test tube 1 and place it into test tube 2. Now add 4mls of distilled water to test tube 2. ...read more.

Conclusion

Measuring the solutions will have to be done properly with care. If the solution volumes tend to change and not be accurate of one test tube, the rest of the test tubes will be affected too. The water bath will have to set to exactly 100�C. the tubes should only be placed in the water bath when the water has reached 100�C and it should remain that temperature throughout. A graduated pipette is accurate for measuring small quantities such as the glucose solution. Measuring the solutions will have to be done properly with care. To gain accurate results from the colorimeter, the cuvettes will have to be wiped and cleaned properly on the sides where the light is to pass through so that the beam of light can pass through without being refracted by smears. The water bath will have to set to exactly 100�C. The tubes should only be placed in the water bath when the water has reached 100�C and it should remain that temperature throughout. For the experiment to remain a fair test care must be taken when using the graduated pipette, it would have to be made sure that there are no air bubbles taking up space affecting the measurements. This is resolved by using the pipette correctly. The glass rod will have to be cleaned after every time it has been used to stir solutions. This is as some solution could stay on the rod and when it is used to stir the next test tube, it could affect the solutions. Whenever I put a number of test tubes in to a water bath, I will place them in a rack, then place the whole rack in the water bath and on removing, remove the whole rack. This will ensure that all the test tubes have had the same amount of time in the water bath. 1 Waseem Riaz ...read more.

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