Potassium dichromate, solution

Of little use commercially except as a route to anthraquinone. For this purpose it is oxidized with acid potassium dichromate solution, or better, by a catalytic air oxidation at 180-280 C, using vanadates or other metal oxide catalysts. 

In what way does a solution of hydrogen peroxide react with (a) chlorine water, (b) potassium permanganate solution, (c) potassium dichromate solution, (d) hydrogen sulphide 50 cm of an aqueous solution of hydrogen peroxide were treated with an excess of potassium iodide and dilute sulphuric acid the liberated iodine was titrated with 0.1 M sodium thiosulphate solution and 20.0 cm were required. Calculate the concentration of the hydrogen peroxide solution in g 1" ... 

Absolute diethyl ether. The chief impurities in commercial ether (sp. gr. 0- 720) are water, ethyl alcohol, and, in samples which have been exposed to the air and light for some time, ethyl peroxide. The presence of peroxides may be detected either by the liberation of iodine (brown colouration or blue colouration with starch solution) when a small sample is shaken with an equal volume of 2 per cent, potassium iodide solution and a few drops of dilute hydrochloric acid, or by carrying out the perchromio acid test of inorganic analysis with potassium dichromate solution acidified with dilute sulphuric acid. The peroxides may be removed by shaking with a concentrated solution of a ferrous salt, say, 6-10 g. of ferrous salt (s 10-20 ml. of the prepared concentrated solution) to 1 litre of ether. The concentrated solution of ferrous salt is prepared either from 60 g. of crystallised ferrous sulphate, 6 ml. of concentrated sulphuric acid and 110 ml. of water or from 100 g. of crystallised ferrous chloride, 42 ml. of concentrated hydiochloric acid and 85 ml. of water. Peroxides may also be removed by shaking with an aqueous solution of sodium sulphite (for the removal with stannous chloride, see Section VI,12). 

Calculate the molarity of a potassium dichromate solution prepared by placing 9.67 g of K2Cr207 in a 100-mF volumetric flask, dissolving, and diluting to the calibration mark. 

The estimation of alkoxy groups is not such a simple task. One method (26,68) involves hydrolysis and oxidation of the Hberated alcohol with excess standard potassium dichromate solution. The excess may then be estimated iodometrically. This method is suitable only for methoxides, ethoxides, and isopropoxides quantitative conversion to carbon dioxide, acetic acid, and acetone, respectively, takes place. An alternative method for ethoxides is oxidation followed by distillation, and titration of the Hberated acetic acid. 

Strychnine, brucine Oxidation is performed with potassium dichromate solution This oxidizes brucine to the o-qumone which can then be separated chromatographically [17]... 

Describe how you would prepare 465 mL of 0.3550 M potassium dichromate solution starting with... 

Mention should be made of one of the earliest internal indicators. This is a 1 per cent solution of diphenylamine in concentrated sulphuric acid, and was introduced for the titration of iron(II) with potassium dichromate solution. An intense blue-violet coloration is produced at the end point. The addition of phosphoric(V) acid is desirable, for it lowers the formal potential of the Fe(III)-Fe(II) system so that the equivalence point potential coincides more nearly with that of the indicator. The action of diphenylamine (I) as an indicator depends upon its oxidation first into colourless diphenylbenzidine (II), which is the real indicator and is reversibly further oxidised to diphenylbenzidine violet (III). Diphenylbenzidine violet undergoes further oxidation if it is allowed to stand with excess of dichromate solution this further oxidation is irreversible, and red or yellow products of unknown composition are produced. 

Experience in this kind of titration may be obtained by determining the iron(II) content of a solution by titration with a standard potassium dichromate solution. 

Prepare 250 mL of 0.02 M potassium dichromate solution and an equal volume of ca 0.1 M ammonium iron(II) sulphate solution the latter must contain sufficient dilute sulphuric acid to produce a clear solution, and the exact weight of ammonium iron(II) sulphate employed should be noted. Place 25 mL of the ammonium iron(II) sulphate solution in the beaker, add 25 mL of ca 2.5M sulphuric acid and 50 mL of water. Charge the burette with the 0.02 M potassium dichromate solution, and add a capillary extension tube. Use a bright platinum electrode as indicator electrode and an S.C.E. reference electrode. Set the stirrer in motion. Proceed with the titration as directed in Experiment 1. After each addition of the dichromate solution measure the e.m.f. of the cell. Determine the end point (1) from the potential-volume curve and (2) by the derivative method. Calculate the molarity of the ammonium iron(II) sulphate solution, and compare this with the value calculated from the actual weight of solid employed in preparing the solution. 

DETERMINATION OF LEAD WITH STANDARD POTASSIUM DICHROMATE SOLUTION... 

Procedure. Prepare a 0.25 per cent solution of diphenylcarbazide in 50 per cent acetone as required. The test solution may contain from 0.2 to 0.5 part per million of chromate. To about 15 mL of this solution add sufficient 3M sulphuric acid to make the concentration about 0.1M when subsequently diluted to 25 mL, add 1 mL of the diphenylcarbazide reagent and make up to 25 mL with water. Match the colour produced against standards prepared from 0.0002M potassium dichromate solution. A green filter having the transmission maximum at about 540 nm may be used. 

Standardisation may be carried out by the use of solutions prepared from a chromium-free standard steel and standard potassium dichromate solution. After dissolution of the standard steel, the solution is boiled with perchloric... 

Potassium chloride (nitrate) bridge 583, 582 Potassium chromate as indicator, 343, 349 Potassium cyanoferrate(II) D. of, (ti) 384 Potassium cyanoferrate(III) D. of, (ti) 399 Potassium cyanonickelate(II) prepn., 328 Potassium dichromate solution analyses involving, 375 oxidising properties of, 375 internal indicators for, 377 preparation of, 0.02M, 375 redox indicators for, 377 standardisation of, by iron, (cm) 546, (ti) 376... 

Kimura and Miller [29] have described a procedure for the determination of organomercury (methylmercury, ethylmercury and phenylmercury compounds) and inorganic mercury in soil. In this method the sample is digested in a steam bath with sulphuric acid (0.9M) containing hydroxy ammonium sulphate, sodium chloride and, if high concentrations of organic matter are present, potassium dichromate solution. Then, 50% hydrogen... 

Procedure Transfer 20 ml of the primary standard solution (Mohr s salt) to the titration flask and add 20 ml of 2 N sulphuric acid. Take the potassium dichromate solution in the burette. Put drops of freshly... 

Assay of lead with potassium dichromate solution... 

Assay of Lead with Potassium Dichromate Solution. 

The primary alcohol or aldehyde is heated under reflux with acidified potassium dichromate solution. For example ... 

Some of the propanal is oxidised to propanoic acid by heating it with acidified potassium dichromate solution. 

Q. Why is the observed absorbance of 2 gg ml zinc dissolved in dilute hydrochloric acid greater than that of 2 gg mb zinc dissolved in 1 M potassium dichromate solution ... 

Tests. Either the neutral-density filters or potassium dichromate solutions are used. 

Potassium Dichromate Solutions. Preparation of the potassium chromate solution differs for the NIST and BP/EP procedures. For the NIST procedure, a solution of potassium dichromate (0.06 g of dichromate per kilogram of solvent) is prepared in 0.001 N perchloric acid. A 0.001 N perchloric acid solution as the reference is scanned and then the potassium dichromate solutions at 235, 257, 313, and... 

Table 10.9. Standard Values for the BP/EP Potassium Dichromate Solution...

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