Alkaline cupric solutions

Benzaldehyde reacts with many chemicals in a marked manner (1) with aramomo-silver nitrate ( Tollen s solution ) to form metallic silver, either as a black precipitate or as an adherent mirror film on glass (but does not reduce alkaline cupric solution. Fehling s solution ) (2) with rosaniline (fuchsine, magenta) that has been decolorized by sulfurous acid ( Schitf s... 

Cuprous oxide is produced in the form of an orange-yellow, amorphous gel containing water by the reduction of an alkaline cupric solution with sodium hyposulphite 7... 

Reduction of Alkaline Cupric Solutions (Fehling s Solution)... 

Reducing sugars Accurately weigh 7 g of sorbitol and transfer to a 400 mL beaker with 35 mL of water and mix. Add 50 mL of alkaline cupric tartrate test solution, and cover the beaker. Heat so that it boils in approximately 4 minutes and boil for 2 minutes. Collect the precipitated cuprous oxide in a tared filtering crucible previously washed with hot water, alcohol, and ether, and then dried at 105 C for 30 minutes. Wash the cuprous oxide on the filter Avith hot water, then with 10 mL of alcohol, and then 10 mL of ether. Dry at 105 C for 30 minutes. The weight of the cuprous oxide should not exceed 50 mg. 

When metallic copper is heated in the air it becomes coated with a layer of oxide, which, according to conditions, may be cuprous or cupric oxide, or a mixture of the two. Pure cuprous oxide is most conveniently prepared in the wet way by treating an alkaline cupric salt solution with a reducing agent, whereby the red cuprous oxide is precipitated. 

A. A 1 50 aqueous solution slowly reduces alkaline cupric tartrate TS at 25°, but more readily upon heating. 

Reducing Substances Transfer about 1 g of sample, accurately weighed, into a 250-mL Erlenmeyer flask, dissolve it in 10 mL of water, add 25 mL of alkaline cupric citrate TS, and cover the flask with a small beaker. Boil gently for exactly 5 min, and cool rapidly to room temperature. Add 25 mL of a 1 10 solution of acetic acid, 10.0 mL of 0.1 N iodine, 10 mL of 2.7 N hydrochloric acid, and 3 mL of starch TS, and titrate with 0.1 N sodium thiosulfate to the disappearance of the blue color. Calculate the weight, in milligrams, of reducing substances (as D-glucose) by the formula... 

Identification Add a few drops of a 1 20 aqueous solution to 5 mL of hot alkaline cupric tartrate TS. A copious red precipitate of cuprous oxide forms. 

Reducing Sugars Dissolve 500 mg of sample in 10 mL of water, warm, and make the solution alkaline with 1 mL of 6 N ammonium hydroxide. Pass hydrogen sulfide gas into the solution to precipitate the iron, and allow the mixture to stand for 30 min to coagulate the precipitate. Filter, and wash the precipitate with two successive 5-mL portions of water. Acidify the combined filtrate and washings with hydrochloric acid, and add 2 mL of 2.7 N hydrochloric acid in excess. Boil the solution until the vapors no longer darken lead acetate paper, and continue to boil, if necessary, until the solution has been concentrated to about 10 mL. Cool, add 5 mL of sodium carbonate TS and 20 mL of water, filter, and adjust the volume of the filtrate to 100 mL with water. Add 2 mL of alkaline cupric tartrate TS to 5 mL of filtrate, and boil for 1 min. No red precipitate forms within 1 min. 

Identification Add 5 mL of 1 N sodium hydroxide to 5 mL of a hot, saturated solution of sample, and gently warm the mixture. The liquid turns yellow and, finally, brown-red. Cool to room temperature, and add a few drops of alkaline cupric tartrate TS. A red precipitate of cuprous oxide forms. 

D. Add 4 mL of alkaline cupric citrate TS to 1 mL of a 1 50 aqueous solution. Boil vigorously for 2 to 4 min. Remove from heat, and allow the precipitate (if any) to settle. The supernatant liquid is blue or blue-green. 

Alkaline Cupric Tartrate TS (Fehling s Solution) See Cupric Tartrate TS, Alkaline. 

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