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.

·  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

______

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 Acid Ion

carbonate +H+ (-2 + 1 = -1) hydrogen carbonate HCO3-

phosphate +2H+ (-3 + 2 = -1) dihydrogen phosphate H2PO4-

Combining the Patterns:

phosphate PO43-

-O (Pattern 1)

+2H+

phosphite PO33- dihydrogen phosphite ______

(Pattern 2) -3 + 2 = -1

Practice Questions:

1.  Write the chemical name or chemical formula for each of the following:

  1. calcium hypochlorite ______
  2. Zn(BrO4)2 ______
  3. barium phosphate ______
  4. SnSO3 ______
  5. Sr(HCO3)2 ______
  6. sodium hydrogen sulfate ______
  7. Cu(H2PO3)2 ______
  8. aluminium dihydrogen phosphite ______