Determination of reducing sugar by Max-Muller

Instruments, laboratory glassware, reagents: electric stove, stopwatch, with a capacity of 25 cm3 pipette, conical flask with a capacity of 150-200 cm3, Bunsen flask, measuring cylinders with a capacity of 50 and 10 cm3, burettes, glass filter, glass rods, and Fehling solution, Fehling solution II, a solution of iron ammonium alum, potassium permanganate solution, distilled water.

Progress definitions

For determination of reducing sugar by Max- Muller to analyze pour water extract prepared in a conical flask with a capacity of 150-200 cm3 consistently make 25 cm3 pipette solution Fehling I and Fehling II. The resulting mixture was heated to boiling and poured with a pipette 50 cm3 of the solution prepared for analysis. Boil exactly 2 minutes, counting the time from the first appearance of the surface bubbles. After boiling, allow the precipitate to settle copper.

A solution of the residue should be blue from excess Fehling solution. If the solution discoloured, indicating partial oxidation of sugar, the analysis should be repeated, slightly decreasing, but exactly measured volume of the filtrate analyzed. In flask add distilled water in an amount that, together with a new volume of 50 cm3. In Bunsen flask carefully decanted test solution without transferring the precipitate to the filter. The precipitate always be covered with liquid to prevent oxidation Su2O oxygen. This residual solution after draining the filter to precipitate copper oxide is added 5-10 cm3 pre- boiled (to remove oxygen) of hot water, and after re- deposition of copper oxide the water was decanted through a filter. Operation washing, sedimentation, decantation with hot water repeated several times until the disappearance of the blue color wash water.

After washing liquid is poured from the flask, and the flask was thoroughly washed with water. Then the conical flask with sediment copper, located under a small layer of wash water, poured to dissolve the precipitate in small portions 30 cm3 solution of iron- ammonium alum. Oxidized copper oxide and iron oxide is reduced to iron. The resulting light- green liquid is poured gently on the glass stick to the same filter in earlier prepared flask. It dissolves copper oxide particles that got into the filter before.

For better dissolution of copper particles surface filter and fluid gently stirred with a glass rod. After dissolution Su2O conical flask and the filter washed well with distilled water, and the liquid from the bulb passed through a filter. The filtrate was titrated by 0.1 M solution of potassium permanganate to neznykayuchoho for 30 s light pink color.

Thus sulphate of iron (II) sulfate passes into iron (III) by the reaction:

10FеSО₄+ 2KMnO₄ + 8Н₂SO₄ = 5Fе(SО₄)₃ + К₂SО₄+ 2МnSО₄ + 8Н₂О

For Max- Müller method for calculating the results of the analysis is based are constant values for copper titer KMnO4 1 cm3 - 10 mg. Therefore, the volume of potassium permanganate taken for titration, multiply by 10 and get the appropriate amount of reducing sugar it.

Mass fraction reducing sugar (glucose, fructose) is calculated as follows:

Х = 100m₁V/1000Mv₁

where m1 - mass of reducing sugar, found by empirical tables mg;

M - mass of the test sample of the product, g;

V - capacity volumetric flask, taken for the preparation of aqueous extract (250 cm3);

V1 - volume of filtrate taken for determination of sugars cm3, 1000 - conversion factor milligrams to grams.

Laboratory work 6

Дата добавления: 2015-11-14