Potassium dichromate, reaction with

Measure 30 ml of a 0.2% potassium dichromate solution with a measuring glass and pour it into a reaction flask. Pour 20-25 ml of a 0.2% hydrogen peroxide solution into another flask. Put both flasks into the bath of the apparatus and keep them there during... 

Preparation and Properties of Chromium(ni) Oxide. (Perform one of the following two experiments.) 1. Take 2.5 g of comminuted potassium dichromate, mix with 0.5 g of sulphur, put the mixture into a porcelain crucible, and heat with the flame of a burner. Perform the experiment in a fume cupboard ) Remove the burner when self-glowing of the mixture is noticeable. Grind the sinter in a mortar with water, filter off the chromium oxide, rinse it, and dry it in a drying cabinet. Write the equation of the reaction. 

Potassium dichromate solutions are indefinitely stable, can be boiled without decomposition, and do not react with hydrochloric acid. Moreover, primary-standard reagent is available commercially and at a modest cost. The disadvantages of potassium dichromate compared with cerium(IV) and permanganate ion are its lower electrode potential and the slowness of its reaction with certain reducing agents. 

F. M. Littersoheid added ammonia to a soln. of potassium dichromate, mixed with an excess of mercuric chloride, in the cold until the liquid had an alkaline reaction and obtained dimercuriammanium chromate, (NHg2)2Cr04.2H20. The same product was obtained by adding an excess of ammonia to a cold soln. of mercuric chloride, and then adding a soln. of potassium chromate or dichromate. The lemon-yeUow precipitate gave off no water when heated for many hours at 100° it is virtually insoluble in water, and in a cold 10 per cent. soln. of ammonia — free from ammonium salts. The moist salt dissolves in soln. of ammonium salts. 

Oxidation, (i) Dissolve 5 g. of potassium dichromate in 20 ml. of dil. H2SO4 in a 100 ml. bolt-head flask. Cool and add 1 ml. of methanol. Fit the flask with a reflux water-condenser and warm gently a vigorous reaction soon occurs and the solution turns green. The characteristic pungent odour of formaldehyde is usually detected at this stage. Continue to heat for 3 minutes and then fit the flask with a knee-tube (Fig. 59, p. 100) and distil off a few ml. Test the distillate with blue litmus-paper to show that it is definitely acid. Then apply Test 3 p. 350) for formic acid. (The reflux-distillation apparatus (Fig. 38, p. 63) can conveniently be used for this test.)... 

Chrome dyes are acid dyes (mol wt 300—600) that contain groups capable of forming complexes by reaction with a metal salt, usually sodium or potassium dichromate (94,97). The chrome/dye complex has lower solubiUty, and hence better wetfastness, than the parent dyestuff. Reaction between the... 

Sihcon carbide is comparatively stable. The only violent reaction occurs when SiC is heated with a mixture of potassium dichromate and lead chromate. Chemical reactions do, however, take place between sihcon carbide and a variety of compounds at relatively high temperatures. Sodium sihcate attacks SiC above 1300°C, and SiC reacts with calcium and magnesium oxides above 1000°C and with copper oxide at 800°C to form the metal sihcide. Sihcon carbide decomposes in fused alkahes such as potassium chromate or sodium chromate and in fused borax or cryohte, and reacts with carbon dioxide, hydrogen, ak, and steam. Sihcon carbide, resistant to chlorine below 700°C, reacts to form carbon and sihcon tetrachloride at high temperature. SiC dissociates in molten kon and the sihcon reacts with oxides present in the melt, a reaction of use in the metallurgy of kon and steel (qv). The dense, self-bonded type of SiC has good resistance to aluminum up to about 800°C, to bismuth and zinc at 600°C, and to tin up to 400°C a new sihcon nitride-bonded type exhibits improved resistance to cryohte. 

Chlorate Analysis. Chlorate ion concentration is determined by reaction with a reducing agent. Ferrous sulfate is preferred for quaHty control (111), but other reagents, such as arsenious acid, stannous chloride, and potassium iodide, have also been used (112). When ferrous sulfate is used, a measured excess of the reagent is added to a strong hydrochloric acid solution of the chlorate for reduction, after which the excess ferrous sulfate is titrated with an oxidant, usually potassium permanganate or potassium dichromate. 

Karrer and Schmid have noted that the dimeride of C-curarine I does not give the characteristic colour reactions of this alkaloid with acids, but still gives that with ceric sulphate and potassium dichromate (p. 384). 

Alkaloid A. This forms a chloride, [CjoHjaONjJ+Cl", HjO, isomeric with the chlorides of toxiferine, C-eurarine I and C-curarine III the picrate has m.p. 269° (dec.). The chloride differs from the isomerides named, in potency, colour reactions and ultra-violet absorption spectrum. The chloride in 2N-sulphuric acid gives a carmine-red colour with potassium dichromate. 

The synthetical experiments started by Openshaw and Robinson have for their immediate objective the preparation of one of the possible degradation products of strychnine, and a beginning has been made by the preparation of the lactam of hexahydrocarbazole-1 ll-/SjS -dipropionic acid (XXIV), which reproduces a portion of the strychnine molecule as represented in Robinson s formula (Ilia, p. 574), and in sulphuric acid gives a purple colour with a trace of potassium dichromate (Otto reaction). 

The first instruments used by police to determine BrAc were developed in the 1930s. Until about 1980, the standard method involved adding K O , which reacts chemically with ethyl alcohol. Potassium dichromate has a bright orange-red color, whose intensity fades as reaction occurs. The extent of the color change is a measure of the amount of alcohol present. 

A solution of potassium dichromate is made basic with sodium hydroxide the color changes from red to yellow. Addition of silver nitrate to the yellow solution gives a precipitate. This precipitate dissolves in concentrated ammonia but re-forms when nitric acid is added. Write balanced net ionic equations for all the reactions in this sequence. 

Alternative procedure. The following method utilises a trace of copper sulphate as a catalyst to increase the speed of the reaction in consequence, a weaker acid (acetic acid) may be employed and the extent of atmospheric oxidation of hydriodic acid reduced. Place 25.0 mL of 0.017M potassium dichromate in a 250 mL conical flask, add 5.0 mL of glacial acetic acid, 5 mL of 0.001M copper sulphate, and wash the sides of the flask with distilled water. Add 30 mL of 10 per cent potassium iodide solution, and titrate the iodine as liberated with the approximately 0.1M thiosulphate solution, introducing a little starch indicator towards the end. The titration may be completed in 3-4 minutes after the addition of the potassium iodide solution. Subtract 0.05 mL to allow for the iodine liberated by the copper sulphate catalyst. 

The reaction of 2-nitrodibenz[6,/]oxepin-10-carboxylic acid with potassium dichromate in acetic acid takes a rather unexpected course 9-methyl-2-nitroxanthene (2) is formed by loss of the carboxylic group and ring contraction.107... 

An accident occurred when 2-propanol reacted with potassium dichromate in a sulphuric medium. The aqueous solution of dichromate and sulphuric acid were added in small quantities. The homogeneous liquid was throwing up glowing particles (CrOj particles ). The same reaction proved not to be dangerous when this process was carried out drop by drop. 

The following reaction often leads to destructive accidents. To avoid this, potassium dichromate in the solid state should not come into contact with the nitrated derivative. 

A sensitive spectrophotometric method was reported for the determination of niclosamide and some other antiamebic and anthelmintic drugs either in pure form or in formulations. The method was based on reduction with Zn and HC1 followed by reaction with metol and potassium dichromate at pH 3.0 to give a colored product having maximum absorbance at 530 nm for niclosamide [54]. 

The analytical procedure is the following [62]. Acetic acid is added to the sample of hydroperoxide, then dissolved air is removed by vacuum the vessel is filled with dinitrogen, and an aqueous solution of SnCl2 is added. The reaction occurs for 1 h at room temperature after this an excess of NH4Fe(S04)2 solution is introduced, and in 30 min the amount of formed Fe(II) is estimated by titration with potassium dichromate. 

During these reactions, orange solutions of potassium dichromate (VI) are reduced to green solutions of chromium (III) ions. Secondary alcohols are oxidised to ketones when heated under reflux with the same reagents. 

Identify the alcohols, in your answers to Question 10, that would undergo oxidation when heated under reflux with a solution of potassium dichromate (VI) in dilute sulphuric acid. Give the structural formula of the final organic product of the reaction in each case. (6)... 

Adogen has been shown to be an excellent phase-transfer catalyst for the per-carbonate oxidation of alcohols to the corresponding carbonyl compounds [1]. Generally, unsaturated alcohols are oxidized more readily than the saturated alcohols. The reaction is more effective when a catalytic amount of potassium dichromate is also added to the reaction mixture [ 1 ] comparable results have been obtained by the addition of catalytic amounts of pyridinium dichromate [2], The course of the corresponding oxidation of a-substituted benzylic alcohols is controlled by the nature of the a-substituent and the organic solvent. In addition to the expected ketones, cleavage of the a-substituent can occur with the formation of benzaldehyde, benzoic acid and benzoate esters. The cleavage products predominate when acetonitrile is used as the solvent [3]. 

In the Breathalyzer test, the subject blows into a tube connected to a vial. The exhaled air collects in the vial, which already contains a mixture of sulfuric acid, potassium dichromate, water, and the catalyst silver nitrate. The alcohol reacts with the dichromate ion in the following redox reaction. 

A( ueous solutions of chromium(ll) sulfate have Ijeen prepared from chromium(lll) sulfate by reduction with zinc powder and from potassium dichromate by reduction with amalgamated zinc and sulfuric acid. Solid chromitim(II) sulfate penlahyrlrate can be obtained from the reaction of highly purified chromium metal... 

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