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Unformatted text preview: ne to form a compound that is not soluble in water. We say that the compound
"falls out" of solution, or pre cipitate s (verb). The solid compound, which has formed, is called a pre cipitate
(noun). As an initial hypothesis, we can state that precipitates will form when the attractive force between ions is
large. This will be true when their charges (q1 and q2) are opposite in sign and large.
As noted previously,
soluble ionic species are mobile and free to move independently of each other. The freedom is not absolute; the
positive ions will not all congregate in one portion of the solution. Nonetheless, the ions are not tied to a position
or to a specific counte rion (ion of opposite charge). To express this, one may write a reaction in the form of a
total ionic e quation, as shown below:
( 14 )
Pb2+(aq) + 2 NO3−(aq) + 2 K+(aq) + 2 I−(aq) → PbI2(s) + 2 K+(aq) + 2 NO3−(aq)
This rather cumbersome equation includes several ions that appear in identical form on both sides of the
equation. These ions are not dir...
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This document was uploaded on 01/22/2014.
- Spring '14