Lead chromate double salts

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 ... 

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. 

Hydroxides and double sulphate have extensively been used, as well as double chromate. The latter one especially has been used for the separation of yttrium from the other rare earths. The addition of sodium sulphate to the rare earth solution leads to the precipitation of double sulphates. The elements La, Ce, Pr, Nd and Sm form poorly-dissolvable double sulphates, whereas Ho, Er, Tm, Yb, Lu and Y form well-dissolvable double salts. The salts of Eu, Gd and Dy form salts of intermediate solubility. Generally, the use of this method cmdely separates the rare earth mixture... 

Rubidium metal alloys with the other alkaU metals, the alkaline-earth metals, antimony, bismuth, gold, and mercury. Rubidium forms double haUde salts with antimony, bismuth, cadmium, cobalt, copper, iron, lead, manganese, mercury, nickel, thorium, and 2iac. These complexes are generally water iasoluble and not hygroscopic. The soluble mbidium compounds are acetate, bromide, carbonate, chloride, chromate, fluoride, formate, hydroxide, iodide. 

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