SCH3U
Oxyanions & Acidanions: Recognizing Patterns
Chemical Reactions
Pattern 1: Oxyanions
Oxyanions (polyatomic ions containing oxygen) have a pattern in their names to indicate the amount of
oxygens. Look at the list of oxyanions that have chlorine in them and see if you notice the pattern.
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The base ion is the one with “ate” and no prefix
When the suffic “ite” is used, subtract 1 oxygen atom from the base ion
When the prefix “hypo” and the suffix “ite” are used, subtract 2 oxygen atoms
When the prefix “per” and the suffix “ate” are used, add 1 oxygen atom to the base ion.
**NOTE: The charge of the polyatomic ion does not change.
Use your polyatomic ions list to find the formulas for the following “base” ions:
Nitrate
carbonate
chlorate
sulfate
phosphate
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Nick the
Camel ate a
Clam for
Supper in
Phoenix
(# vowels = charge #consonants = number of oxygen atoms)
Use the 5 base polyatomic ions above and fill in the boxes below with the 3 other polyatomic ions that can
be known from the base ion.
Name
Formula
Name
Formula
Name
Formula
Name
Formula
Name
Formula
Pattern 2: Acidanions
-an acid anion is created when one or more H+ ions covalently bond with an oxyanion (ie. HCO3-, HPO42-)
-when acid anions conbine with cations, acid-salts are created (Ie. CaHPO4)
-using the base polyatomic ions from the above and the pattern below, you can create the acid anions.
Base Ion
carbonate
phosphate
+H+ (-2 + 1 = -1)
+2H+ (-3 + 2 = -1)
Acid Ion
hydrogen carbonate HCO3dihydrogen phosphate H2PO4-
Combining the Patterns:
phosphate PO43-
-O
(Pattern 1)
+2H+
phosphite PO33-
dihydrogen phosphite
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(Pattern 2) -3 + 2 = -1
Practice Questions:
1. Write the chemical name or chemical formula for each of the following:
a. calcium hypochlorite
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b. Zn(BrO4)2
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c. barium phosphate
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d. SnSO3
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e. Sr(HCO3)2
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f. sodium hydrogen sulfate
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g. Cu(H2PO3)2
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h. aluminium dihydrogen phosphite ________________________________________