Strontium carbonate sulphate

The method consists in first converting the sulphate into the carbonate by boiling it with a concentrated solution of sodium carbonate, and then dissolving the carbonate in hydrochloric acid, thereby yielding a solution of the chloride. The conversion of solid strontium sulphate into solid strontium carbonate furnishes an interesting illustration of the solubility product principle, for the solubility of these two salts in pure water is as follows ... 

Strontium sulphate would dissolve in the solution of sodium carbonate in the same manner as it would in pure water until it had saturated the solution, and its solubility product, which is equal to 0.0006 X 0.0006, was reached, but for the fact that long before this could occur the solution would be supersaturated with respect to strontium carbonate, the solubility product of which is only equal to 0.00007 X 0.00007. Thus strontium carbonate is precipitated continuously as strontium sulphate dissolves and since the solution cannot become saturated with the latter as long as a large excess of carbonate ions is present, the solid salt finally remaining will consist entirely of strontium carbonate, provided a sufficient amount of sodium carbonate were employed. The reaction which takes place is, however, reversible, SrSO + Na2C03 SrCOj + NasSO, and, if strontium carbonate were boiled with a solution of sodium sulphate, the solid would change into sulphate until carbonate ions had accumulated in the solution to such an extent as to make the concentration ratio [C03 ] [SO4 ] = 1 74. When this ratio prevails, both solids are in equilibrium with the solution and no change takes place in either direction. 

Explain why strontium carbonate, which is less soluble in pure water than strontium sulphate, should dissolve readily in dilute acids, while the latter salt will dissolve scarcely any more in acids than in pure water. 

Sodium nitrate III Sodium nitrite VIII Sodium peroxide IV, Q. 61 Sodium sulphate Q. 3, II Sodium tetraborate Q. 23 Starch, soluble IV, VII, VIII Strontium carbonate P. 21 Sugar, cane III, VIII Sulphur, flowers II, IV, VIII Tartaric Acid III... 

Strontium carbonate is less soluble than strontium sulphate (solubility 5-9 mg SrC03 1, Ks = 1-6 x 10-9 at room temperature). 

Manufacture. Strontium carbonate occurs naturally as a strontium ore, but the production is not large. Celestine(consisting mainly of SrSO and containing Ca and Ba) is heated with sodium carbonate to form a melt, and the product is then washed with water to remove the strontium sulphate. 

The most common precipitates encountered in brackish water desalination are calcium and magnesium carbonate, sulphates of calcium, barium, and strontium. 

The alkali metals of Group I are found chiefly as the chlorides (in the earth s crust and in sea water), and also as sulphates and carbonates. Lithium occurs as the aluminatesilicate minerals, spodimene and lepidolite. Of the Group II metals (beryllium to barium) beryllium, the rarest, occurs as the aluminatesilicate, beryl-magnesium is found as the carbonate and (with calcium) as the double carbonate dolomite-, calcium, strontium and barium all occur as carbonates, calcium carbonate being very plentiful as limestone. 

STRONTIUM.—Although less abundantly diffused, it resembles barium both in ita chemical and geological relations. Like it strontium is neveT found native, hut only as carbonate and sulphate. It was first recognized by Hope in 1792, in the mineral sirontiantte, so called from Strontian in Scotland. 

If a small quantity of a solution of strontium chloride were added to a solution containing equimolal quantities of sodium carbonate and sodium sulphate, what would be the precipitate formed ... 

Commercial zinc sulphate invariably contains a small amount of iron as an impurity. Since FeS04-7H20 crystallizes isomor-phously with ZnS04-7H20 a preparation of the latter cannot be freed of the former by recrystallization. By addition of chlorine, or its equivalent, to the solution of zinc sulphate, the iron is oxidized to ferric salt the ferric salt hydrolyzes somewhat, and, if the acid produced by the hydrolysis is neutralized as fast as formed, the hydrolysis proceeds to completion and all the iron is precipitated as Fe(OH)3. In this case, the reagent used to bring about the exact neutrality of the solution is a suspension of basic zinc carbonate. (Compare the similar procedure for removing traces of iron in the preparation of strontium chloride, Preparation 21.)... 

The filtrate must be acidified immediately and concentrated to remove H2S. Ammonium sulphide solution on exposure to air slowly oxidizes to ammonium sulphate and would then precipitate any barium or strontium present as BaS04 or SrS04. Another reason for the immediate acidification of the filtrate from Group IIIB is to prevent the absorption of C02 from the air with the attendant formation of carbonate ions the latter would also precipitate the ions of Group IV. 

Instead of the rather expensive precipitated chalky salts of strontia, carbonate of calcium, and the native sulphate of strontium (coelestine), may be used for preparing red fire according to the following receipts ... 

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