QrASTJTA 7717; AC,HH'rLTl'RAL

1 4

piuhsr of ! lir' Millet is tivatod on pages 13S to 140, Hpw-

rvrr. nc should note here that in making titrations in analytical
4'hfmistry w aro usually not concerned with existing ion con-
ct'utrati<m#, but rather with total ionizable or titraiable hydrogen

cir Imlroxyl. In other words, we seek complete calculated
Mfutrality, with chemically equivalent quantities of titrated and
titrating substances present, rattier than what might be called

electrolytic neutrality, where PB equals 7.

v ,*/ 20 30 40 50 60 TO 60 90 100 Up HO 130
Mg.-cq.of bascfor arcScfj added h I00m0.-eq.ofacid (or base)
FIG. 1.—Typical titratioa curves. Indicator ranges are: 1-TkymoI blue; 2-
Methyl orange; 3-Methyl red; 4-Brom thymol blue; 5-Phen.ol red; 6-Phenol-
phtholein; 7-Alizarin yellow.
The curves shown in Kg. 1 illustrate the variation of P&
values as titration proceeds, In a few typical cases. As the
titrating standard is added to a definite quantity of the titrated
substance, the value for Ps changes with regularity. Two essen-
tial conditions must obtain, in order that a sharp end point may
be observed. These are (a) that the neutralization curve must
show a steep inclination at the point of equivalent neutrality
(f.€., that a very slight increase in the amount of standard solution
shall produce a relatively large change in hydrion concen-
tration at this point) and (6) that the range of Pff over which the