Page:Outlines of Physical Chemistry - 1899.djvu/257

 CHEMICAL EQUILIBRIUM

��tion a quantity x of the nitric acid (a) decomposes a corresponding quantity of the sulphate (6) setting sulphuric acid (a x ) free. We shall then have in solution

(1 — x) b + (1 — x) a + x b x + x a x.

The change in volume will be equal to x times the expansion which would take place if the reaction were a complete one, plus the effect produced by the free sulphuric acid on the remaining sulphate. If we put this in algebraic

form we get

x x 8*17 +[aja! x(l- x) b].

If we accept the conclusion which we deduced from the thermo- chemical study — namely, that the reaction takes place to the extent of 66 per cent, or two-thirds — then the expansion which should be observed is

§ x 8 # 17 + £ x 4-625 = 7 cubic centimetres.

This calculated result has been experimentally con- firmed so that the two methods of investigation, the thermo- chemical and the volumetric, indicate the same division of the base between the two acids.

By this volumetric method Ostwald determined the relative avidity of nitric acid, hydrochloric acid, and sulphuric acid with reference to different bases.

Avidity ratio

��Bases

EOH

NaOH

NH S.

£MgO

iZnO

iCuO

��HNO,

�HCl

�HCl

�HNO,

��The avidity ratio TT _ T ,

��is constant for all bases.

��Sulphuric acid behaves somewhat irregularly, — its avidity being greater when referred to Mg, Zn, Cu, and

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