Sample Problem 2.8
Determining Names and Formulas of Ionic Compounds Containing Polyatomic Ions
PLAN:
SOLUTION:
Polyatomic ions have an overall net charge. When writing a formula with more than one polyatomic unit, place the ion in parentheses.
(a) Fe(ClO4)2
(b) sodium sulfite
(a) ClO4- is perchlorate; the iron ion must have a 2+ charge. This is iron(II) perchlorate.
(b) The sulfite anion is SO32-. Therefore you need two sodium ions per sulfite ion. The formula is Na2SO3.
(c) Hydroxide anion is OH- and barium is a 2+ ion. When water is included in the formula, the term “hydrate” and a prefix indicating the number of waters are used. So it is barium hydroxide octahydrate.
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