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.

1.2. 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.

Reaction with 2,6-dichlophenolindophenol.

Ascorbic acid acidifies by 2,6-dichlophenolindophenol to dehydroascorbic acid, and reagent itself reduces at that to uncoloured compound.

Reagent and facility: cabbage or potatoes juice; test tube; burette; 2,6- dichlophenolindophenol, sodium salt, 0,001n; salt acid, 2% sol.

Technique definition.

1 ml cabbage or potatoes juice pour in test-tube, add 3-4 drops of 2% spirit of salt and dropwise solution of 2,6-dichlophenolindophenol. Reagent will discolor till all ascorbic acid acidify to dehydroascorbic, after which still first drop of solution colors liquid in pink, because 2,6-dichlophenolindophenol any more restores.

3. Reaction with potassium ferricyanide. Ascorbic acid, when acidify, reduces potassium ferricyanide K₄Fe(CN)₆ to ferrocyanide K₄Fe(CN)₆, which with ion ferric forms in acidic medium ferric ferrocyanide Fe4[Fe(CN)₆]₃.

Reagent and facility: cabbage or potatoes juice; test tube; dropping-bottle; potassium ferricyanide, 5% sol.; potassium hydroxide, 5%sol.; salt acid,10%sol.; ferrichloride, 1%sol.

Technique definition.

To 1 ml cabbage or potatoes juice add 2 drops of caustic potash solution, just as much solution of potassium ferricyanide and shake test tube, whereupon add drop wise 10% spirit of salt and 1-2 drops of solution ferrichloride. Dark blue or greenish-dark blue sediment of ferric ferrocyanide separate out, which show that there is ascorbic acid.

 

Test questions

1. What are reducing properties of ascorbic acid.?
2. By what elements does ascorbic acid in the light reduce?

Laboratory job №9

Theme: Definition of fats mass share in cans by refractometric method and total acidity in canned goods with sour fillings

The purpose of work: Definition of refraction coefficient of fat solution in solvent- naphthalene monobromate, by which fats are pulled out preliminary from researched product and experimental definition of total acidity in canned goods with sour fillings.

1.1 The task

1. Definition of fat’ mass fraction by refractometric method.

To make skills and attainments of definition by refractometric method.

2. Definition of total acidity in canned goods with sour fillings

3. Draw up report on the work done.

1.2. Theoretical part

Method is founded on pulling out fat from sample with the help of naphthalene monobromate and definition refraction index of solvent and solution of fat in solvent with the help of refractometer. Naphthalene monobromate well dissolves fat in the cold and have high rate of refraction, differ markedly from from refraction index of fat. On dissolving of fat by naphthalene monobromate refraction index decrease at amount, proportional amount of fat resolve.

In canned goods with sour fillings total acidity is normed. So, acidity in recalculation on an apple acid must be from 0,3 up to 0,6 %.