This historic book may have numerous typos and missing text.
Purchasers can download a free scanned copy of the original book
(without typos) from the publisher. Not indexed. Not illustrated.
1921 Excerpt: ... solution during the process of titration, and
hence the sharper will the end point be. Very marked weakness
alone, however, is not the deciding factor, as this in itself
brings in certain effects, such as hydrolysis, to which reference
will be made. Asa typical acid indicator we may take
phenolphthalei'n. This acid is extremely weak. The undissociated
molecule is colourless. When completely dissociated, say, in the
form of its sodium salt, the solution is bright pink, which must be
due to the anion, since Na has no colour effect in the visible
spectrum. In acid solution, i.e. in presence of relatively large H'
concentration, the dissociation of phenolphthalei'n will be thrown
back so as to be practically undissociated, and hence the solution
is colourless. In alkaline solution--excess of 0H'--the H' produced
by the indicator acid will unite with 0H' to 1 The conductivity
method in a modified form differing from that described has been
employed.by Walker (Zeitscli. physik. Chem., 4, 333, 1889) to
measure the hydrolysis of chlorides and sulphates of weak bases.
give H20, and this process goes on until dissociation of the
indicator is practically complete, and hence the solution is
brightly coloured. Since the indicator is weak, a small drop of
titrating acid or alkali will cause a sufficient change in the
relative H' and 0H' concentration to cause the above marked colour
change. As a typical basic indicator we may instance methyl orange.
In alkaline solution the indicator is yellow, in acid, red. The
yellow colour is due to the undissociated molecule, the red to the
cation. Methyl orange contains a sulphonic acid group, which at
first sight would lead us to think that this indicator is an acid
one. That this is not the case, however, has been shown by
|Country of origin:
William Cudmore McCullagh Lewis
||246 x 189 x 10mm (L x W x T)
||Paperback - Trade
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