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investigating the amount of ascorbic acid present in fruit

Extracts from this document...

Introduction

Investigating the Amount of Ascorbic Acid Present in Fruits: Aim: To investigate the amount of ascorbic acid present in samples of fruit. Introduction: What is Ascorbic Acid and Why It Is Needed: Ascorbic acid is another name for vitamin C and is an essential vitamin needed for everyday life. Vitamin C is also soluble in water, which is important to humans since we are unable to synthesize our own ascorbic acid within the liver. It is also an antioxidant (which can help prevent cancer) and is added to foods to protect their colour and aroma. Furthermore ascorbic acid is used to prevent the oxidation of fats and oils by atmospheric oxygen, resulting in the development of rancid flavours. In addition ascorbic acid is vital for the production of collagen (intermolecular substance that gives bones, teeth and cartilage their structure). Other reasons why it is needed include: * Synthesis of bile acids * Maintaining skin elastic * Assists in iron absorption * Improves resistance to infection Deficient Amount of Ascorbic Acid: An insufficient diet of ascorbic acid should be best avoided to refrain from these symptoms such as: * Fatigue * Insomnia * Loss of appetite * Minor capillary bleeding In a very severe case: * Scurvy (in which the legs are shaped in an abnormal way). Using Titration to find out the Known Amount of Vitamin C: The titration method can be used to find out the amount of ascorbic acid that is present in samples of fruit and vegetables. Once a permanent colour change has happened, this is when end point has been reached. The solution will go from a colourless to a dark blue-black colour, when it it is titrated against a known concentration of N -Bromosuccinimide solution. The presence of the blue-black is due to the KI and starch solution reacting together, the KI acts as an indicator by having the presence of iodide and acetic acid acts as a 'source of acidic solution'. ...read more.

Middle

23. Finally repeat the procedure again with a different sample of fruit (once having finished titrating with previous fruit sample), so that you can compare the vitamin C content with the fruits. Justification for Getting Accurate Results: Before and whilst making up my acid solutions and doing my titration, there was a number of things I had to do to make sure that I got accurate results: Use of 1ml and 5ml Pipettes: * Pipettes have been cleaned with distilled water before use. * Pour whatever is about to be pipetted from a beaker, not straight from the reagent bottle. * Before pipetting, make sure that the pipette is not blocked from the tip. * When transferring the 4% KI and 5% H2SO4 to the 250cm3 conical flask, the tip of the pipette must be lightly tapped against the conical flask so that all of it goes in. Thus increasing accuracy. Use of the 50cm3 Burette: * The burettes are cleaned with NBS solution (since that is what is going to be used in the titration). * No air bubbles are present. * The burette tip is not damaged. * The tap is not leaking. * The burette is in a vertical position, whilst being held in place by the clamp. * That the outside of the burette is clean, so that it is clear to see what volume was used to decolourise the ascorbic acid solution. Titration Check List: * Check that the balance is clean before weighing out the solid acetic acid and KI. * Balance is set to 0.00g. * The weighing boat is placed in the middle of the balance. * Repeat titration until results are in 0.1 of each other. * The weighing boat is dry and clean. * Use white tile whilst recording the volume. * Take funnel off whilst doing the titration. * Make sure that 4.00g of the solid KI and 10.00g of the solid acetic acid has been accurately weighed. ...read more.

Conclusion

Before weighing out the solid KI and acetic acid, the balance was set to 0.00g and that the weighing boat was placed in the middle of the balance. Also if there were bits of solid acetic acid and KI I made sure to use distilled water to take out any bits that may be left on the weighing boat. When starting the titration I made sure to take off the funnel (preventing inaccuracies in results). When recording the volume I made to use a white tile, kept good eye-level and the dip was on the meniscus line. To make sure that the experiment was justified and consistent, I repeated the titration until my results were 0.1 of each other. When coming near to my endpoint I added in the NBS solution drop by drop, so that I got the correct measurement when a permanent colour change has happened. When I finished with the titration experiment I made sure to clean out the conical flask and beakers with distilled water. Time Keeping: I think that I could have done the experiment a lot quicker at the start of the experiment if I had centrifuged with four test tubes rather then two. Centrifuging with only two test tubes at a time wasted time and effort. Although once I had four test tubes, the centrifuging process went a bit quicker. Another problem with the centrifuging process was not knowing exactly the amount of time it would take for the fruit juice sample to separate the bits from the liquid. If I would have done things differently I would have learnt how to use the centrifuge before starting the experiment, rather then learning during the investigation. Another problem I had with the centrifuge was the fact that at times I did not put the test tubes into the centrifuge properly, so when I switched the centrifuge on, all the test tubes ended up falling out. Thus spilling the fruit juice sample and having to cut up another piece of fruit again. ...read more.

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