Chemistry I Polyatomic Ions
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1Chemistry I
Polyatomic Ions
Here’s a list of common polyatomic ions and acids:
Ion
Name
Acid Formula
Acid Name
+
NH
Ammonium*
4
-
NO
Nitrate
HNO
Nitric Acid
3
3
-
NO
Nitrite
HNO
Nitrous Acid
2
2
-
OH
Hydroxide*
HOH
Water (not really an acid)
-
CN
Cyanide
HCN
Hydrocyanic Acid
-
SCN
Thiocyanate
HSCN
Thiocyanic Acid
-
ClO
Perchlorate*
HClO
Perchloric Acid
4
4
-
ClO
Chlorate*
HClO
Chloric Acid
3
3
-
ClO
Chlorite*
HClO
Chlorous Acid
2
2
-
ClO
Hypochlorite*
HClO
Hypochlorous Acid
-
C
H
O
Acetate
HC
H
O
Acetic Acid
2
3
2
2
3
2
-
MnO
Permanganate
HMnO
Permanganic Acid
4
4
2-
SO
Sulfate*
H
SO
Sulfuric Acid
4
2
4
2-
SO
Sulfite*
H
SO
Sulfurous Acid
3
2
3
-
HSO
Hydrogen sulfate or
H
SO
Sulfuric Acid
4
2
4
Bisulfate*
2-
S
O
Thiosulfate
H
S
O
Thiosulfuric Acid
2
3
2
2
3
2-
CO
Carbonate
H
CO
Carbonic Acid
3
2
3
-
HCO
Hydrogen carbonate or
H
CO
Carbonic Acid
3
2
3
bicarbonate
2-
CrO
Chromate
H
CrO
Chromic Acid
4
2
4
2-
Cr
O
Dichromate
H
Cr
O
2
7
2
2
7
2-
O
Peroxide
H
O
Hydrogen Peroxide (not
2
2
2
really an acid)
2-
C
O
Oxalate
H
C
O
Oxalic Acid
2
4
2
2
4
3-
PO
Phosphate*
H
PO
Phosphoric Acid
4
3
4
2-
HPO
Hydrogen Phosphate*
H
PO
Phosphoric Acid
4
3
4
-
H
PO
Dihydrogen Phosphate*
H
PO
Phosphoric Acid
2
4
3
4
Hints to help you remember these ions:
•
For the asterisked (*) ions, you can figure out their charge from the non-oxygen element and the periodic table.
-
Example: ClO
: Cl corresponds to a 1- charge on the periodic table.
3
•
-
-
-
-
Changing the number of Oxygens does not change the charge. Example: ClO
, ClO
, ClO
, ClO
4
3
2
•
3-
2-
-
Adding Hydrogens increases the charge by +1. Examples: PO
, HPO
, H
PO
4
4
2
4
•
+
Ammonium (NH
) is the only + polyatomic ion you need to know.
4
•
3-
Phosphate (PO
) is the only 3- polyatomic ion you need to know.
4
•
“Per-X-ate” à loses oxygen à “X-ate” à loses oxygen à “X-ite” à loses oxygenà “hypo-X-ite”
Hints to help you remember the acids:
•
“Per-X-ate” ion corresponds to “Per-X-ic Acid”
•
“X-ate” ion corresponds to “X-ic Acid”
•
“X-ite” ion corresponds to “X-ous Acid”
•
“Hypo-X-ite” ion corresponds to “hypo-X-ous Acid”
What about acids of mono-atomic anions? (Where anion ends in –ide) Like HCl? Or HF? “Hydro-X-ic Acid”
HCl
Hydrochloric Acid
HF
Hydrofluoric Acid
HCN
Hydrocyanic Acid
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