ACIDS, BASES AND SALTS. 65- Copper Hydride.
From 100 c.c. of a 5% solution of barium hypophosphite
(No. 96), precipitate all of the barium by the addition of about
18 c.c. of 2-normal sulphuric acid, and treat the clear filtrate
at the room temperature with four grams of copper sulphate dis-
solved in 15 c.c. of water. After some time, or more quickly if
heated to 30°, the solution becomes green, and dark-brown copper
hydride is precipitated which to some extent adheres to the sides
of the glass vessel as an iridescent film. Filter off the precipitate,
wash it with water, and dry the product in a vacuum-desiccator.
Heat a portion of the copper hydride in a small test-tube. It
decomposes suddenly into red copper and hydrogen; the latter
may be ignited at the mouth of the tube.
Cover a second portion with concentrated hydrochloric acid;
hydrogen is evolved, which, in consequence of the admixed spray
of copper compounds, burns with a deep-blue flame. From the
solution in the test-tube, the addition of a little water precipitates
white cuprous chloride.
ACIDS, BASES, AND SALTS.
The majority of the simple compounds are electrolytes, that is, they are
acids, bases, or salts. The preparation of simple electrolytes can take place
according to the methods outlined on p. 51 as generally applicable for simple
compounds; as peculiar to electrolytes, the formation of a compound by
the association of its ions, presents a special case of synthesis from the ele-
ments. In the preparation of pure electrolytes in solution by bringing
together the necessary ions, it is essential that foreign ions should be removed.
Thus soluble hydroxides may be prepared by precipitating solutions of the
corresponding sulphates with an equivalent amount of barium hydroxide,
the barium and sulphate ions being removed as insoluble barium sulphate,
and only the desired hydroxide and its ions remaining in solution (cf.
No. 36). In a similar way acids may be obtained by the interaction of
barium salts and sulphuric acid (No. 33). Potassium iodide, likewise, may
be prepared conveniently by the double decomposition of ferrous iodide with
potassium carbonate, whereby iron and carbonate ions are precipitated in
the form of an insoluble compound (No. 39).
ELECTROLYTIC DISSOCIATION is distinguished from simple dissociation by
the fact that the products of dissociation are electrically charged. Further-
more, the extent of electrolytic dissociation depends in the highest degree upon
the nature of the solvent medium.
2 HI = H 2 + I2 (non-electrolytic dissociation).
HI = H+ + I~ (electrolytic dissociation).