Potassium dichromate

HUMAN CARCINOGEN AS DUST, CONTACT WITH COMBUSTIBLE MATERIAL MAY CAUSE FIRE 

Mixtures of boron and potassium dichromate with or without silicon may ignite.2 

Hydroxylamine. Aqueous hydroxylamine ignites on contact with potassium dichromate moistened with sulfuric acid. The anhydrous base explodes violently on contact with potassium dichromate.3 

Dust is destructive to the tissues of mucous membranes, respiratory tract, and eyes. Swallowing causes irritation and internal damage and may be fatal. Prolonged skin exposure can result in ulceration, damage to liver and kidneys, and even cancer. Avoid inhaling dust. Avoid contact with eyes and skin.4 TLV-TWA 0.05 mg/m3.5 

Small Quantities. Wear eye protection, laboratory coat, and nitrile rubber gloves. In the fume hood, add solid potassium dichromate to a container of water (about 100 mL/5 g). Acidify with 3 M sulfuric acid (35-55 mL, pH 1 with pHydrion paper). While stirring, slowly add solid sodium thiosulfate (about 13.5 g) until the solution becomes cloudy and blue colored. Neutralize the solution with sodium carbonate. After a few minutes a blue-gray flocculent precipitate is formed. Let the mixture stand for a week or filter immediately through Celite. After a week, much of the supernatant can be decanted. The remaining liquid is allowed to evaporate or the solid filtered. The liquid may be washed into the drain. The solid residue should be washed with hot water to remove sodium sulfate, and then dried, packaged, labeled, and sent to a secure landfill site.6 

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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. 

Diamond is very resistant to chemical reagents potassium dichromate and sulphuric acid attack it with the formation of CO2. It burns in air or oxygen at 700 C to CO2 leaving scarcely any ash some forms of bort may leave as much as 4-5% ash. 

Thus under standard conditions chloride ions are not oxidised to chlorine by dichromate(Vr) ions. However, it is necessary to emphasise that changes in the concentration of the dichromate(VI) and chloride ions alters their redox potentials as indicated by the Nernst equation. Hence, when concentrated hydrochloric acid is added to solid potassium dichromate and the mixture warmed, chlorine is liberated. 

Addition of dilute potassium dichromate(VI) solution, K2Cr207, to a solution of hydrogen peroxide produces chromium peroxide, CrOj, as an unstable blue coloration on adding a little ether and shaking this compound transfers to the organic layer in which it is rather more stable. 

This reaction is a useful test for a sulphite or for moist sulphur dioxide, which turns dichromate paper (filter paper soaked in potassium dichromate) from yellow to green. 

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" ... 

If the chloride is heated with sodium or potassium dichromate-(VI) and concentrated sulphuric acid, a red gas, chromium(VI) dichloride dioxide, CrOjClj, is evolved if this is passed into water, a yellow solution of a chromate(VI) is formed. 

Addition of an oxidising agent to a solution of an iodide (for example concentrated sulphuric acid, hydrogen peroxide, potassium dichromate) yields iodine the iodine can be recognised by extracting the solution with carbon tetrachloride which gives a purple solution of iodine. 

Sodium sulphate crystallises out in hydrated form (common ion effect) and is filtered off on concentration, sodium dichromate is obtained. For analytical purposes, the potassium salt. K2Cr20-. is preferred potassium chloride is added and the less soluble potassium dichromate obtained. 

The dichromate ion oxidises iron(II) to iron(III), sulphite to sulphate ion, iodide ion to iodine and arsenic(III) to arsenic(V) (arsenate). Reduction of dichromate by sulphite can be used to prepare chrome alum, since, if sulphur dioxide is passed into potassium dichromate acidified with sulphuric acid, potassium and chromium(III) ions formed are in the correct ratio to form the alum, which appears on crystallisation ... 

Thus, filler paper which has been dipped into a solution of potassium dichromate turns green in the presence of sulphur dioxide. This reaction provides the usual test for sulphur dioxide. 

Octan-2-ol (A), sometimes called sec.octy alcohol, can be obtained, at a low price and of high purity, from technical sources. As a secondary alcohol, it can be readily oxidised by potassium dichromate-sulphuric acid to n-hexyl... 

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.)... 

Dissolve I drop of quinoline in 1 ml. of dil. HCl and add a few drops of a saturated solution of potassium dichromate. A copious orange-yellow precipitate of quinoline dichromate, (C,H7N)2 HjCrj07, is formed pyridine does not give a crystalline dichromate under these conditions. 

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). 

CAUTION. Ethers that have been stored for long periods, particularly in partly-filled bottles, frequently contain small quantities of highly explosive peroxides. The presence of peroxides may be detected either by the per-chromic acid test of qualitative inorganic analysis (addition of an acidified solution of potassium dichromate) or by the liberation of iodine from acidified potassium iodide solution (compare Section 11,47,7). The peroxides are nonvolatile and may accumulate in the flask during the distillation of the ether the residue is explosive and may detonate, when distilled, with sufficient violence to shatter the apparatus and cause serious personal injury. If peroxides are found, they must first be removed by treatment with acidified ferrous sulphate solution (Section 11,47,7) or with sodium sulphite solution or with stannous chloride solution (Section VI, 12). The common extraction solvents diethyl ether and di-tso-propyl ether are particularly prone to the formation of peroxides. 

By the oxidation of secondary alcohols with potassium dichromate and dilute sulphuric acid, for example ... 

The compound is employed inter alia as an indicator In titrations with potassium dichromate and ceric siilphate solutions. 

The following factors are the equivalent of 1 mL of normal potassium dichromate. Where the normality of the solution being used is other than normal, multiply the factors given in the table below by the normality of the solution employed. 

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. 

Cross-linking agents potassium dichromate zinc chromate borates... 

Breath alcohol testing is accompHshed by a number of techniques. The oldest rehable procedure involves bubbling a measured volume of deep-lung air containing alcohol through an acidic solution of potassium dichromate, Deep-lung air is the last portion of expired breath. It is collected in... 

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