Potassium tellurate

Potassium pemnanganate Potassium nitrite Potassium nitrate Potassium sulphite Potassium stannate IV Potassium sulphate Poptassium metabisulphite Potassium peroxodisulphate Potassium tellurate (IV) Potassium pyrophosphate... 

Tellurates. The water-soluble alkali metal and alkaline-earth tellurates are prepared by chlorinating alkaline solutions of the tellurites or by heating solid tellurites with KN03, KQ03, or Pb02 to form, for example, potassium tellurate [7790-58-1], Iv-TeO,. The insoluble tellurates are made by... 

Potassium tellurate,15 K2Te04.—At 20° C. the solubility of the tellurate is 27-53 grams per 100 grams of water.16... 

According to Gutbier, the addition of a uranyl salt to a solution of potassium tellurate yields a yellow curdy precipitate of uranyl tellurate. 

SYNONYMS Synonyms vary depending upon the specific tellurium compound, (tellurium) aurum paradoxum, metallum poblematum, tellurium, metallic, (hydrogen telluride) dihydrogen telluride, tellurium hydride, (potassium tellurite) potassium tellurate (IV). 

Potassium tellurate(VI) trihydrate K3Te03 3H3O 16671-91-2 323.84 wh cry powder sH,0... 

Thirty milliliters of sodium hydroxide solution (0.02 g./ml.), 10 to 15 ml. of potassium thiocyanate J or potassium tellurate(IV),t and 70 ml. of distilled water are placed in a 500-ml. reaction flask (Fig. 11). The pH of this solution is about 10. The mixture is boiled for 30 minutes with the stopcock open to remove dissolved air. The heating is stopped and the stopcock closed simultaneously. When the temperature drops to 20°, 10 ml. of freshly reduced vanadium(II) sulfate solution, containing about 0.1 g. of vanadium(II), is added directly from the electrolytic cell... 

Neutral beryllium tellurates and tellurites were precipitated by potassium tellurate or tellurite as white voluminous flakes. 

Kormal potassium tellurate, K TeO + 6HjO, obtained upon evaporation of a sdutiou, dther in the form of crystalline oTusle, cv as a gum like residue, both being sduble in water. 

The yellow modification of this sslbis obtdned when salt No. 2 is heated to redness. On adding water to tiie leddne, normal potassium tellurate dissolves out, and a tetmtellnrate remains behind, bdi insolnble in vrabw and in dOnte adds. 

Fluor-jod, n. iodine fluoride, -kalium, n. potassium fluoride, -kalzium, n. calcium fluoride, -kiesel, m. silicon fluoride, -kie-selsaure,/. fluosilicic acid, -kohlenstoff, m. carbon fluoride, -lithium, n. lithium fluoride. -metall, n. metallic fluoride, -natrium, n. sodium fluoride, -phosphat, n. fluophosphate. -phosphor, m. phosphorus fluoride, -salz, n. fluoride, -schwefel, m. sulfur fluoride, -selen, n. selenium fluoride, -silber, n. silver fluoride, -silikat, n. fluo-silicate. -silizium, n. silicon fluoride, -sili-ziumverbindung, /. fluosilicate. -tantal-sMure, /. fluotantalic acid, -tellur, n. tellurium fluoride, -titan, n. titanium fluoride, -toluol, n. fluorotoluene, fluotoluene. 

Also, telluric acid can be prepared by oxidation of tellurium or tellurium dioxide with a strong oxidizing agent such as hydrogen peroxide, sodium peroxide, chromic acid, or potassium permanganate in nitric acid. Molecular equations for overall reactions are shown helow ... 

A number of substances, such as the most commonly used sulfur dioxide, can reduce selenous acid solution to an elemental selenium precipitate. This precipitation separates the selenium from most elements and serves as a basis for gravimetry. In a solution containing both selenous and tellurous acids, the selenium may be quantitatively separated from the latter by performing the reduction in a solution which is 8 to 9.5 N with respect to hydrochloric acid. When selenic acid may also be present, the addition of hydroxy] amine hydrochloride is recommended along with the sulfur dioxide. A simple method for the separation and determination of selenium(IV) and molybdenum(VI) in mixtures, based on selective precipitation with potassium thiocarbonate, has been developed (69). 

When the oxychloride is warmed with potassium perdisulphate, chlorine is evolved if sulphuric acid is present the reaction occurs in the cold. Chlorine is also evolved from selenium oxychloride when warmed with telluric or selenic acid. 

Different types of methods for purification have been applied. Brauner in 1889, by means of aqua regia, converted crude tellurium into telluric chloride, the aqueous solution of which on precipitation by sulphur dioxide deposited the element together with selenium and traces of copper and lead as the only impurities. The precipitate was dissolved in fused potassium cyanide in an atmosphere of hydrogen and the tellurium separated from the aqueous extract by treatment with a current of air. The element was then distilled in a current of hydrogen, 1 an alternative is distillation in a vacuum.5 Another method of treatment for the telluric chloride solution is to precipitate in three fractions using sulphur dioxide, when it is found that the middle fraction is of a high degree of purity.6... 

Marckwald, after a research with unsatisfactory material,4 prepared some pure tellurium dioxide from telluric acid which had been crystallised several hundred times.5 The dioxide was analysed volumetrically by oxidising to telluric acid by means of potassium permanganate, excess of the latter being determined by means of oxalic acid. The mean result obtained was 127-61. 

The use of sulphur dioxide as precipitant was first proposed by Berzelius, but accurate results by this method are only obtainable under special conditions. Complete precipitation does not take place from a strongly acid solution, and in the presence of other metals small amounts of these are liable to be carried down. In the presence of heavy metals such as copper, bismuth and antimony, the following procedure has been recommended 2 The tellurium is oxidised to telluric acid by the addition of ammonium perdisulphate in the presence of potassium hydroxide, excess of perdisulphate being subsequently removed by boiling. The heavy metals present are next removed by means of hydrogen sulphide. The tellurium may then readily be estimated by reduction with hydrogen chloride and precipitation with sulphurous acid. 

Tellurous acid is rapidly reduced to the element by sulphurous acid in the presence of potassium iodide.3 Owing, however, to the affinity which tellurium has for iodine and the consequent formation of varying proportions of tellurium tetra-iodide, the trustworthiness of the quantitative method based on this reaction is questionable.4... 

Volumetric Estimation.—Tellurium may be determined by oxidation from the tellurous to the telluric condition, using an excess of potassium dichromatc or permanganate and subsequently titrating the excess of oxidising agent with a standard solution of a suitable reducing agent.2 In order to obtain accurate results with the potassium dichromate titration, certain very definite steps in the procedure are essential, and it is necessary to control the course of the reaction, since hydrochloric and telluric acids interact with production of chlorine. 

Tellurous acid cannot be determined by oxidation with potassium permanganate in acidified solution, but in alkaline solution accurate results may be obtained by cooling to 8°-10° C. after the oxidation and slowly acidifying with dilute sulphuric acid, with continual stirring. Excess of standard oxalic acid is then added and after warming to 50° C. the remaining excess is titrated with permanganate.6... 

Telluric acid may be determined iodometrically by reduction with either hydrogen bromide or hydrogen chloride.6 The substance is heated in a distillation llask with four times the theoretical quantity of potassium iodide in the presence of the acid, air being excluded from the apparatus by passing a stream of carbon dioxide. The liberated iodine is titrated in the receiver and in the residue.7... 

By treatment with sufficiently strong oxidising agents, such as chromic acid or potassium permanganate with hydrochloric or sulphuric acid, aqueous solutions of salts of basic tellurium are converted into solutions of telluric acid.17... 

Tellurium Dioxide as an Acid Anhydride.—When tellurium tetrachloride is treated with water, or when an aqueous solution of a tellurium salt is decomposed by an aqueous alkaline solution, a bulky, colourless precipitate is obtained which is sufficiently soluble in water to impart an acid reaction to the solution and which is more readily soluble than tellurium dioxide in acids or alkalis. A similar precipitate is obtained on acidifying a cold aqueous solution of potassium tellurite with a slight excess of nitric acid. This product is a tellurous acid, possibly H2TeOs, but it is very unstable and spontaneously dehydrates, slowly at the ordinary temperature and rapidly at 40° C. with formation of dioxide.1... 

A concentrated solution of telluric acid boiled with a solution of potassium thiocyanate yields a yellow, heterogeneous, amorphous precipitate, containing tellurium, carbon and nitrogen.8... 

---