Potassium Acetate Solution Chromate

Lead azide is dissolved by an aqueous solution of ammonium acetate, but it is not destroyed by it. The solution contains azide ions and lead ions, the latter quantitatively precipitable as lead chromate, PbCr04, by the addition of potassium dichromate solution. Lead azide in aqueous suspension is oxidized by ceric sulfate with the quantitative production of nitrogen gas which may be collected in an azotometer and used for the determination of the azide radical. 

Lead acetate solution white precipitate of lead sulphate, PbS04, soluble in hot concentrated sulphuric acid, in solutions of ammonium acetate and of ammonium tartrate (see under Lead, Section III.4, reaction 5), and in sodium hydroxide solution. In the last case sodium tetrahydroxoplumbate(II) is formed, and on acidification with hydrochloric acid, the lead crystallizes out as the chloride. If any of the aqueous solutions of the precipitate are acidified with acetic acid and potassium chromate solution added, yellow lead chromate is precipitated (see under Lead, Section III.4, reaction 6). 

Heat with sodium carbonate and potassium nitrate This test may be carried out in a loop of platinum wire or upon platinum foil or upon a piece of broken porcelain. If chromium is present, a yellow melt is produced. This should be dissolved in water, acidified with dilute acetic acid, and (a) silver nitrate solution added, when brownish-red silver chromate is precipitated, (6) lead acetate solution added, when yellow lead chromate is precipitated, or (c) 1-2 ml diphenylcarbazide reagent added, when a deep-red colouration is produced. 

Double salts of lead chromate with alkali chromates have been obtained. The potassium salt, K3Cr04.PbCr04 or KaPb(Cr04)2, is formed as a yellow amorphous precipitate when SO c.c. of a saturated solution of potassium chromate is mixed with 10 c.c. of saturated lead acetate solution. The ammonium salt, (NH4)2Pb(Cr04)2, is prepared similarly, and both salts are decomposed into their components by %vater. 

Five grams (0.0127 mol) of (-t-)-bis(l,2-ethanediamine)(oxalato)-cobalt(III) iodide ([a] = -1-720°) is converted to the acetate by shaking for 10 min with 2.11 g (0.0126 mol) of solver acetate suspended in 30 mL of hot (50°) water contained in a 100-mL flask. The precipitated silver iodide is removed by filtration and washed with 10 mL of hot water. The combined red filtrate and washings are added with stirring to a solution of 2.00 g (0.00409 mol) of racemic potassium tris(oxalato)chromate(III)... 

Synftiesis is by adding a neutral solution of a soluble lead salt (acetate or nitrate) to an alkali (usually potassium or sodium) chromate or dichromate solution (Beam, 1923) Kittel (1960) states that chrome yellow may also be made directly by adding lead monoxide to chromates in paste form. From the work of Vauquelin (1809), Kuhn and Curran suggest that lead chromate was introduced as a pigment between 1804 and 1809. 

Solutions of the following salts are usually 0.5 M with respect to the hydrated salt ammonium thiocyanate, copper sulphate, iron(IIl) chloride, iron(II) sulphate, potassium iodide, potassium thiocyanate. Solutions of the following salts are usually 0.25 M barium chloride, calcium chloride, lead acetate, potassium chromate, potassium hexacyanoferrate(II), tin(II) chloride (with few pieces of Sn to stop aerial oxidation), zinc nitrate. 

Methyl 3-Carbethoxyoxy-7-keto-12a-hydroxycholanate. A solution of 4 g (8.6 mmoles) of crude methyl 3-carbethoxyoxycholate in 50 ml of acetic acid containing 10 g of sodium acetate trihydrate is treated gradually with a solution of 3 g (0.015 mole) of potassium chromate in 8 ml of water with shaking. After 10 hr at 25° the solution is diluted with water and the product collected by filtration to afford 3.9 g (97%) of methyl 3-carbethoxyoxy-7-keto-12a-hy-droxycholanate, mp 150-158°. Crystallization from methanol gives hard, compact needles or rods mp 157-158° 41°. The same substance is... 

Lead chromate is found naturally in minerals crocoite and phoenicochroite. It also is readily prepared by adding a soluble chromate such as sodium or potassium chromate to a solution of lead nitrate, lead acetate or other soluble lead(II) salt in neutral or slightly acidic solution ... 

The crude substance is their recrystallised from water containing acetic acid. The compound was originally believed to exist in two isomeric forms, but Jorgensen found the crystalline form depends on the concentration of acetic acid used for crystallisation, inasmuch as rhombic leaflets separate from hot dilute acetic acid, and from hot concentrated acid the substance separates in yellow-brown needles. The complex is sparingly soluble in water, and gives no precipitate in aqueous solution with silver nitrate or potassium chromate. If treated with cold hydrochloric acid it is transformed into chloro-dinitro-triammino cobalt, [Co(NH3)3(N02)2Cl], and if warmed with concentrated hydrochloric acid gives diehloro-aquo-triammino-cobaltic chloride. 

Synonym Neatsfoot Oil Necatorina Nechexane Neutral Ahhonium Pluoride Neutral Anhydrous Calcium Hypochlorite Neutral Lead Acetate Neutral Nicotine Sulfate Neutral Potassium Chromate Neutral Sodium Chromatetanhydrous Neutral Verdigris Nickel Acetate Nickel Acetate Tetrahyorate Nickel Ammonium Sulfate Nickel Ammonium Sulfate Hexahydrate Nickel Bromide Nickel Bromide Trihydrate Nickel Carbonyl Nickel Chloride Nickel Chloride Nickel Cyanide Nickel Iiu Fluoborate Nickel Fluoroborate Solution Nickel Fluoroborate Nickel Formate Nickel Formate Dihyorate Nickel Nitrate Nickel Nitrate Hexahydrate Nickel Sulfate Nickel Tetracarbokyl Nickelous Acetate Nickelous Sulfate Nicotine Nicotine Sulfate Nifos Nitralin Nitram O-Nitraniline P-Nitraniline Nitric Acid Nitric Acid, Aluminum Salt Nitric Acid, Iron (111) Salt Compound Name Oil Neatsfoot Carbon Tetrachloride Neohexane Ammonium Fluoride Calcium Hypochlorite Lead Acetate Nicotine Sulfate Potassium Chromate Sodium Chromate Copper Acetate Nickel Acetate Nickel Acetate Nickel Ammonium Sulfate Nickel Ammonium Sulfate Nickel Bromide Nickel Bromide Nickel Carbonyl Nickel Chloride Nickel Chloride Nickel Cyanide Nickel Fluoroborate Nickel Fluoroborate Nickel Fluoroborate Nickel Formate Nickel Formate Nickel Nitrate Nickel Nitrate Nickel Sulfate Nickel Carbonyl Nickel Acetate Nickel Sulfate Nicotine Nicotine Sulfate Tetraethyl Pyrophosphate Nitralin Ammonium Nitrate 2-Nitroaniline 4-Nitroaniline Nitric Acid Aluminum Nitrate Ferric Nitrate... 

Prepare about 30 g. of normal lead chromate, PbCr04 (Exercise 23), by the double decomposition of lead acetate and potassium dichromate and wash the precipitate until it is free from soluble lead salts. Suspend the yellow chromate in a dilute solution of sodium hydroxide (1 20) and boil until the color has changed to a bright brick red. This material is a basic chromate known as chrome red, having the composition represented by the formula PbCr04-PbO ... 

In the manner described in the preceding exercise, prepare several tubes half filled with a gel obtained by mixing equal parts of water glass (density, 1.06) and acetic acid (0.5 normal) and with the addition of enough potassium chromate to make the solution 0.1 normal with respect to the latter salt. The chromate should be added to the water glass before the addition of the acetic acid. 

Cobalt Chromate, CoCr04, is prepared by heating cobalt carbonate and chromic acid solution for several hours at 185° C. in a sealed tube.5 It yields greyish black crystals, readily soluble in hot dilute nitric acid (contrast nickel chromate). The dihydrate, CoCr04.2H20, is obtained by the interaction of cobaltic acetate and potassium chromate. It yields bronze-coloured prisms or leaflets.5... 

Potassium chromate in neutral, acetic acid or ammonia solution yellow precipitate of lead chromate... 

Potassium chromate solution no precipitate from dilute solutions, nor from concentrated solutions in the presence of acetic acid (cf. Section III.31, reaction 6). 

Potassium chromate solution Treat 2 drops of the test solution with 1-2 drops K2Cr04 solution. Note the formation of a yellow precipitate.. Centrifuge and wash. Add 2 drops dilute acetic acid to the precipitate and stir note that the precipitate does not dissolve. 

J)) Mix equal small quantities of potassium carbonate, potassium nitrate, and powdered chrome alum, place the mixture on a platinum foil, and hold it with the forceps in the upper Bunsen flame so that the mixture will fuse. If a platinum foil is not available, use a porcelain crucible. A yellow mass, due to the presence of potassium chromate, results. If the color is not decided, dissolve the mass in water, add acetic acid, slowly at first, and boil to expel the carbon dioxide. Add a few drops of lead nitrate solution to a portion, and yellow lead chromate is precipitated. (Compare Exp. 177 (e).) If the precipitate is white, it is lead carbonate, and shows that not all the potassium carbonate was decomposed, as intended. 

Potassium Chlorochromate, CrOj.OK.Gl, may be obtained [a) by warming together a mixture of potassium dichromate and concentrated hydrochloric acid b) by the action of ehromyl chloride upon a solution of potassium chloride or upon aqueous potassium chromate acidified with acetic acid (c) by fusion of potassium dichromate with chromic chloride or (d) by interaction of phosphorus trichloride and potassium dichroraate. ... 

Silver chromate is almost insoluble in water, glacial acetic acid, and in solutions of potassium chromate, but soluble in those of ammonia, caustic alkalies, nitrates, and in dilute acetic acid. A concentrated solution of ammonium nitrate is a good crystallising medium for silver chromate. With chlorine, above 200° C., silver chloride, chromium trioxide, and oxygen are produced. The solution in ammonia contains the compound Ag2Cr04.4NH3, which forms crystals isomorphous with the corresponding ammoniacal sulphate. ... 

After the passage of the gas the liquid is evaporated in a platinum (or porcelain) capsule on the water bath to a volume of 2-3 ml. and then 2 drops of acetic acid are added and the evaporation continued almost to dryness. The residue is redissolved in 2-3 ml. water and again evaporated to dryness to decompose the sodium biacetate which is formed. The residue is once more dissolved in 2 ml. water, a drop of potassium chromate solution added and then titrated with N/40 silver nitrate. It is advisable to carry out a blank determination. The amount of phosgene present in the sample is calculated from the number of ml. of N/40 silver nitrate solution employed in titration. 

A modern version of dichromate oxidation in aqueous media is a phase-transfer reaction carried out in a two-phase system. Alkaline di-chromate is converted into tetraalkylammonium dichromate, which is soluble in organic solvents such as dichloromethane, chloroform, or benzene ( orange benzene ). The treatment of alcohols with a solution of potassium dichromate in acetic acid in the presence of Adogen 464 (Aldrich s trade name for methyltrialkyl [Cg-Cio] ammonium chloride) and benzene gives aldehydes at 55 °C [651. Similar results are obtained with a chloroform solution of tetrabutylammonium chromate at 60 °C [618]. ... 

Figure 4-2 An experiment to demonstrate the presence of ions in solution. Two copper electrodes are dipped into a liquid in a beaker. When the liquid contains significant concentrations of ions, the ions move between the electrodes to complete the circuit (which includes a light bulb), (a) Pure water and sugar are nonelectrolytes, (b) A solution of a weak electrolyte, acetic acid (CH3COOH) it contains low concentrations of ions, and so the bulb glows dimly, (c) A solution of a strong electrolyte, potassium chromate (K2Cr04) it contains a high concentration of ions, and so the bulb glows brightly.

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