Synthetic Inorganic Chemistry

132 THE THEORY OF IONIZATION

of lead iodide is 0.002 F.W. per liter, the concentration of Pb++

ions is 0.002, and the concentration of I~ ions is 0.004 in the

saturated solution. The solubility product of

Pbl 2 = [Pb++] [I~]^2 = 0.002 X 0.004^2 = 0.000,000,032

To determine the solubility of Pbl 2 in a 0.1 formal solution of KI

let x = F.W. of Pbl 2 per liter. Then x = [Pb++] and 2x + 0.1 = [I"]

[Pb++] [F]^2 = x (2x + 0.1)^2 = 0.000,000,032

Solving, x = 0.000,003, and therefore the solubility of Pbl 2 in 0.1

formal KI is 0.000,003 F.W. per liter.

PROBLEMS

95. The molal solubility of AgBrO 3 at 24.5° is 0.0081.
    How many grams of AgBrO 3 could dissolve in a liter of 0.1
    molal AgNO 3? Assume complete ionization of the salts.


96. The solubility of PbSO 4 is 0.04 gram per liter at 25°.
    How many grams of sodium sulphate should be added to
    1 liter to reduce the solubility of the lead sulphate to 0.0001
    gram per liter?

HYDROGEN ION CONCENTRATION; THE pH SCALE
The properties common to all acids are due to hydrogen ions,
but there are two ways in which the extent of the effect of hydro-
gen ions must be gauged. In the first place the normality of an
acid solution is a measure of the amount of base it will neutralize.
One liter of 1N strong acid, such as HCl, will neutralize the same
amount of base as 1 liter of IN weak acid, such as HC 2 H 3 O 2.
The normality of an acid thus measures the total amount of avail-
able hydrogen ions. Yet the concentration of the active or ionized
hydrogen in the HCl is about one hundred times as great as in the
HC 2 H 3 O 2. Vinegar is about 3 per cent or 0.5N acetic acid. Its
taste is sour, but it is possible to hold it in the mouth and even
swallow some of it. On the other hand, 0.5N HCl is so extremely
sour that it cannot be held in the mouth. The sour taste is pro-
portional to the active H+ ion concentration. Many other physi-
ological effects, as well as effects in promoting industrial chemical
reactions, are likewise proportional to the active H+ ion concen-
tration rather than to the total available H+ ion, and it becomes