A report on task performance
Test questions
1. How to prepare a standard solution of tannin
2. How to determine the total phenol content in the fruit.
3. How to build a calibration curve
Laboratory work # 7
Determination of ascorbic acid’ content by iodometric method.
Purpose of the work: experimental determination of ascorbic acid’ content by iodometric method.
1.1. The task
1. Learn the bases of iodometric method .
2. Define ascorbic acid’ content by iodometric method.
3. Draw up report about the effort.
Theoretical part
A redox titration, involving an iodometric method, will be used to do the analysis. The samples will be classified by their ascorbic acid content.
Although most mammals can synthesize vitamin C, or ascorbic acid (C6H8O6), from sugars, man must ingest considerable quantities of this substance. The National Academy of Sciences recommends the consumption of 60 mg of ascorbic acid per day. Vitamin C deficiency refers to a condition where the body does not have enough vitamin C to perform important functions. Humans, unlike many animals, cannot manufacture vitamin C on their own — they must consume it as part of their diet. This vitamin helps build and maintain healthy bones and teeth; build tendons, cartilage, skin, and collagen; and heal wounds.
Technique definition.
5-10g of coarsely cut product pour by 1% spirit of salt (not above 20ml) in mortar, grind until indiscrete mass and carry over into 100ml measuring flask. Wash the mortar and add 2% solution of metaphosphoric acid till mark, leave to stand for 10min and filter at once into dry flask. Then take out three 5-20ml’ samples of filtrate (according to content of ascorbic acid). Add a small crystal of potassium iodide (KJ) and several drops of 1% amylase in two parallel samples and titrate from microburet by 0,001mol/dm3solution of iodic potassium(KJO3) until violet color.
If you determine ascorbic acid’ content in colored solutions, put the3d flask nearby to compare color. The volume 1ml of 0,001mol/dm3solution of iodic potassium corresponds 0,088ml of ascorbic acid.
Calculation of ascorbic acid’ content (Xa) is carried by formula:
Xa= V·T ·V1·100/ m·V2, where
V- quantity of 0,001mol/dm3solution of iodic potassium, taken for titration of extract, ml;
T- titre -0,088 mg of ascorbic acid, responding 1 ml of 0,001mol/dm3solution of iodic potassium;
100- correction coefficient of ascorbic acid’ content;
V2- volume of filtrate of being investigated product, taken for titration, ml;
m-weighed amount of product, g.
Test questions
1.What is the formula of ascorbic acid?
2. Why man must ingest considerable quantities of this substance?
3.Why it is necessary to add a small crystal of potassium iodide (KJ)?
Laboratory work #8
Analysis of reducing properties of ascorbic acid.
Purpose of work: analyze reducing properties of ascorbic acid.
1.1. The task
1. Learn the bases of reducing properties of ascorbic acid..
2. Define reducing properties of ascorbic acid.
3. Draw up report about the effort.
Theoretical part
Ascorbic acid is a naturally occurring organic compound with antioxidant properties. It is a white solid, but impure samples can appear yellowish. It dissolves well in water to give mildly acidic solutions. Ascorbic acid is one form ("vitamer") of vitamin C. It was originally called L-hexuronic acid, but when it was found to have vitamin C activity in animals ("vitamin C" being defined as a vitamin activity, not then a specific substance), the suggestion was made to rename L-hexuronic acid. The new name for L-hexuronic acid is derived from a- (meaning "no") and scorbutus (scurvy), the disease caused by a deficiency of vitamin C. Because it is derived from glucose, many animals are able to produce it, but humans require it as part of their nutrition. Other vertebrates lacking the ability to produce ascorbic acid include other primates, guinea pigs, teleost fishes, bats, and birds, all of which require it as a dietary micronutrient (that is, a vitamin).[2]
Chemically, there exists a D-ascorbic acid which does not occur in nature. It may be synthesized artificially. It has identical antioxidant properties to L-ascorbic acid, yet has far less vitamin C activity (although not quite zero).[3] This fact is taken as evidence that the antioxidant properties of ascorbic acid are only a small part of its effective vitamin activity. Specifically, L-ascorbate is known to participate in many specific enzyme reactions which require the correct epimer (L-ascorbate and not D-ascorbate).
1. Reaction with methylene blue. Ascorbic acid in the light reduces by methylene blue to uncolored compound , acidifing to dehydroascorbic acid.
Reagents and facility: cabbage or potatoes juice; test tube; grate from nonrusting steel; mull; methylene blue,0,01% sol.; natrium carbonate, 5% sol..
Technique definition.
Potato tuber or part of cabbage head grate on grater from nonrusting steel. Ground mass squeeze out through mull, mounted in two layers.
To 1ml of new- succus of potatoes or cabbage add drop wise of methylene blue and 2-3 drops of soda solution. Test tube slightly heat. See after discoloration of blue color.