Fehlings titration

If n is the total dilution to which the original filtrate is subjected to obtain the solution used in the Fehling titration, and a the number of c.c. of the diluted solution required to decolorise the 50 c.c. of Fehling solution, the lactose (hydrated) L contained in 100 grams of the milk analysed is given by the formula ... 

From the data of the Fehling titration (see 2, a), the number of c.c. F of Fehling solution which would be reduced by the total reducing sugars present in 100 grams of milk is calculated by means of the formula2 ... 

The inverted solution obtained from the fruit (40 grams in 200 c.c. 50 c.c. of this inverted and made up to 100 c.c.) gave the reading + 32, so that Px = + 320 Fehling titration of the same inverted solution indicated 54 20% of total reducing sugars. 

An old-fashioned chemist would perform sugar analyses by Fehlings titration before and after inversion and polarimetry. A technique very... 

Several variations of the chemical method are in use. In the one described below, a freshly prepared Fehling s solution is standardised by titrating it directly against a standard solution of pure anhydrous glucose when the end-point is reached, I. e., when the cupric salt in the Fehling s solution is completely reduced to cuprous oxide, the supernatant solution becomes completely decolorised. Some difficulty is often experienced at first in determining the end-point of the reaction, but with practice accurate results can be obtained. The titrations should be performed in daylight whenever possible, unless a Special indicator is used (see under Methylene-blue, p. 463). 

Repeat the titrations until consistent values (i.e., values which do not differ by more than 0 1 ml. of glucose solution) are obtained. Then calculate the weight of glucose equivalent to 1 ml. of the Fehling s solution. 

Weigh out accurately about 1 25 g. of the sample, dissolve it in water and make the solution up to 250 ml. Titrate this solution against 25 ml. of the standard Fehling s solution, precisely as before. 

Ofner Method. This method is for the determination of invert sugar in products with up to 10% invert in the presence of sucrose and is a copper-reduction method that uses Ofner s solution instead of Fehling s. The reduced cuprous oxide is treated with excess standardized iodine, which is black-titrated with thiosulfate using starch indicator. 

For analysis by titration with Fehling s solution, the sample is treated with lead acetate to precipitate protein and fat, filtered, and the filtrate titrated with alkaline CuS04, while heating. The reactions involved are summarized in Figure 2.37. 

After half an hour s saccharification, titration with Fehling s solution indicated 2-144 grams of maltose per 200 c.c. of the solution, i.e., 5360 grams of... 

Ascorbic acids reduce Fehling solution in the cold, and react with ferric chloride to produce the violet color typical of enolic compounds. They are readily oxidized reversibly to their primary oxidation products, 2,3-glycodiulosono-1,4-lactones (commonly known as dehydroascorbic acids 148, Scheme 16), by such mild oxidizing agents as aqueous iodine. Titration with such oxidants constitutes a quantitative method for distinguishing ascorbic acids from 2-glyculosonic acids. 

Invert Sugar Conduct a preliminary test to ascertain the volume of water to be added to the 20 mL of Standardized Fehling s Solution to obtain a final total volume of 75 mL when the endpoint of the titration is reached. The invert sugar content of the Sample Solution should be between 250 and 400 mg per 100 mL so that a titer between 25 and 40 mL is needed to achieve the endpoint. Calculate the amount of water to be added to the Mixed Fehling s Solution as the difference... 

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