Atomistry » Tungsten » Compounds » 12-Tungstoboric Acid
Atomistry »
  Tungsten »
    Compounds »
      12-Tungstoboric Acid »

12-Tungstoboric Acid, H9[B(W2O7)6]

12-Tungstoboric Acid, H9[B(W2O7)6].28H2O, is prepared by the addition to 1 part of normal sodium tungstate and 1.5 parts of boric acid of sufficient water to form a clear solution on boiling. After a time a mixture of sodium borate and boric acid separates. This is filtered off, the mother-liquor is treated with more boric acid, a further precipitate is rejected, and the solution treated with sulphuric acid and ether according to Drechsel. The resulting oil is decomposed by cold water, and on evaporation in a vacuum, crystals of two isomeric acids separate simultaneously; those in larger quantity being transparent octahedra of 12-tungstoboric acid, H9[B(W2O7)6].28H2O; those in smaller quantity, hexagonal bipyramidal crystals of iso-12-tungstoboric acid, H9[B(W2O7)6].22H2O. The first acid is isomorphous with the 28-hydrates of the 12-tungsto- and 12-molybdo-phosphoric and silicic acids. It melts at 45° to 51° C. The addition of nitric acid to its concentrated solution precipitates a lower hydrate containing 10H2O. The hydrogen-ion concentration in a 0.05 N solution is 3.5×10-3.

A well-defined series of crystalline salts, of composition R5H4[B(W2O7)6].xH2O (R = NH4, Li, K, Na, Ag; R2 = Ba, Ca, Cd, Cu, Mg, Ni), has been obtained by careful addition of the metal hydroxide or carbonate to 12-tungstoboric acid. These salts are isomorphous with the corresponding salts of other 12-heteropoly acids; for instance, in addition to the examples already given, the sodium salt, Na5H4[B(W2O7)6].27H2O, is isomorphous with the similarly constituted sodium metatungstate, Na6H4[H2(W2O7)6].27H2O. The equivalent conductivities of solutions of the sodium salt, containing 1/5 molecule in v litres at 25° C., have been found to be:

v =32641282565121024
Λ =183.9196.0203.2213.6225.3235.3

These values correspond with those of a neutral pentabasic salt, but the neutralisation curve shows that at least two more of the hydrogen atoms are replaceable. A guanidinium salt, (CN3H6)6H3[B(W2O7)6], has been obtained, and, according to Copaux, the addition of mercurous nitrate to a solution of the sodium salt yields a crystalline precipitate of the normal mercurous salt, Hg9[B(W2O7)6].12H2O.

Last articles

Zn in 7M6U
Zn in 7NNG
Zn in 7NEE
Zn in 7NEU
Zn in 7M3K
Zn in 7KWD
Zn in 7KYH
Zn in 7KNG
Zn in 7KY2
Zn in 7KYF
© Copyright 2008-2020 by
Home   |    Site Map   |    Copyright   |    Contact us   |    Privacy