Page 77 - Pharmaceutical Analytical Chemistry II - Pharm D- 02-06-07102
P. 77
Iodide ion forms with mercuric ion a very stable complex (pK=
30.2). The reaction can be used to estimate iodides or mercuric salts by
titrating the iodide with a mercuric ion when a soluble colorless complex
is first formed. Near the end point, excess mercuric ions decompose the
complex and produce red mercuric iodide, thus;
4 I- + Hg2+ → HgI42-
HgI42- + Hg2+ → 2 HgI2 (red ppt)
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