Aqua regia reagent

Tetrafluoroethylene. Emulsion polymerisation of tetrafluoroethylene, catalysed by oxygen, yields polytetrafluoroethylene (Tejlon) as a very tough horn-hke material of high melting point. It possesses excellent electrical insulation properties and a remarkable inertness towards all chemical reagents, including aqua regia. 

Sonnenschein s reagent (alkaloid detection) a nitric acid solution of ammonium molybdate is treated with phosphoric acid. The precipitate so produced is washed and boiled with aqua regia... 

Aqua regia is basically a mixture of nitric and hydrochloric acids (Jabir s recipe would have also contained sulphuric acid), and it is one of the few chemical reagents potent enough to corrode gold. The metal forms a complex in which each gold atom combines with four chloride ions this complex is soluble in water. The disappearance of immortal gold when treated with aqua regia must have seemed miraculous to the alchemists. 

The nitro-pentammino-iridium salts resemble those of chromium, cobalt, and rhodium, and react similarly towards reagents, but they are more stable towards acids. They give on long heating with hydrochloric acid chloro-pentammino-derivatives, but are not decomposed by concentrated nitric acid nor by aqua-regia, and only slowly decompose on heating with concentrated sulphuric acid at 100° C. ... 

It is evident that other methods end reagents may be adopted. For example, the original solution In aqua regia may be concentrated by evaporation, until it is very much reduced in quentlty then add about throe-fourths of its bulk of spirit of wine, and, lastly, a saturated solution of chloride of ammonium. By these reagents the platinum will be thrown down as a yellow Crystalline precipitate, while the solution filtered from this, and treated with sulphate of iron or boiled with oxalic acid, deposits geld. 

Nitrophenol on filter paper deposited in a waste basket can give rise to an unexpected explosion Nitrosyl chloride, NOC1, the reddish-brown gas dissolved in aqua regia is a very reactive reagent. It reacts with most of the elements and with many of the compounds, and is very corrosive in the presence of water (Ref 115)... 

The student should remember from qualitative analysis that white zinc sulfide dissolves readily in dilute HC1, that yellow cadmium sulfide may be dissolved in concentrated HC1, but that black mercuric sulfide (one of the least soluble salts known) requires the action of a trifunctional reagent such as aqua regia (Exercise 1). 

Figure 2.20 Grain-boundary and intragranular precipitation at the hot side of the hot-gas casing of a gas turbine. Material is 321 stainless steel. Etched successively in Vilella s reagent, methanolic aqua regia, and Groesbeck s reagent to darken carbides. (Reprinted with permission from ASM International. All rights reserved www.asminternational.org)...

High-purity (99.99%) platinum in the form of either thin wire or foil is recommended as a starting material because of its ease of dissolution in aqua regia all other chemicals should be of reagent-grade quality and are usable without additional purification. 

If the reagent is added in excess, a dark-brown colloidal solution is formed which runs through the filter paper. If the colloidal solution is boiled or if it is rendered slightly acid with acetic acid and boiled, the colloidal solution (hydrosol) is coagulated and can then be filtered. The presence of large quantities of ammonium chloride usually prevents the formation of the sol. Nickel sulphide is practically insoluble in cold dilute hydrochloric acid (distinction from the sulphides of manganese and zinc) and in acetic acid, but dissolves in hot concentrated nitric acid and in aqua regia with the separation of sulphur ... 

Examine for Pb, Bi, Cu, and Cd by Table VII.6 in Section VII.23. After separation of Cu and Cd, acidify the solution with dilute HC1, introduce a few zinc granules and after several minutes filter off any solid and wash with water. Dissolve the ppt. in 2 ml aqua regia, evaporate just to dryness, dissolve the residue in 2m HC1 and add dimethylglyoxime reagent. 

The presence of gold in any of the precipitates described can be detected by solution in aqua regia, and reduction to metallic gold by various reagents, including ferrous chloride, ferrous sulphate, mercurous nitrate, stannous chloride, hypophosphorous acid, oxalic add,3 sulphurous acid, hydrogen peroxide and potassium hydroxide, formaldehyde, and hydroxylamine hydrochloride.4... 

Chromium is a white, hard, lustrous, and brittle metal (mp 1903 10°C). It is extremely resistant to ordinary corrosive agents, which accounts for its extensive use as an electroplated protective coating. The metal dissolves fairly readily in nonoxidizing mineral acids, for example, hydrochloric and sulfuric acids, but not in cold aqua regia or nitric acid, either concentrated or dilute. The last two reagents passivate the metal in a manner that is not well understood. The electrode potentials of the metal are... 

---