 LESSON
Oxidation State Practice
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Oxidation State Practice

Body text Rule 1: For pure elements (unbonded or only bonded with itself), each atom has an oxidation number of zero

• The oxidation state of Na in Na is zero (0)

• The oxidation state of H in H2 is zero (0)

Q.

What is the oxidation state of S in S8?

-2

-16

0

2

Rule 2: Monatomic (single) ions have oxidation numbers equal to their charge.

• The oxidation state of Na+ is +1

• The oxidation state of S2- is -2

Rule 3: Oxygen’s oxidation number is -2 except when in peroxides (such as H202), where it is -1.

• A peroxide is a compound containing 2 +1 cations and 2 oxygen ions

• The oxidation state of O in Na2O2 (sodium peroxide) is -1

Q.

What is the oxidation state of C in CO?

+4

-4

+2

-2

Rule 4: Hydrogen’s oxidation number is +1, except for when bonded to metals as the hydride ion forming ionic compounds.

• The oxidation state of H in H2O is +1

• The oxidation state of H in NaH is -1

Q.

What is the oxidation state of N in HNO3?

+5

-3

-1

-5

Rule 5: Fluorine (F) has an oxidation number of -1 in ALL of its compounds

• NO EXCEPTIONS!!

Rule 6: Halogens (Cl, Br, I) have negative oxidation numbers when they form halide compounds. When combined with oxygen, they have positive numbers, except for F.

• The oxidation state of Cl in HCl is -1

• The oxidation state of Cl in HClO3 is +5

Q.

What is the oxidation state of Br in HBrO4?

-1

-7

+7

-5

Rule 7: In a neutral atom or molecule, the sum of the oxidation numbers must be 0. In a polyatomic ion, the sum of the oxidation numbers of all the atoms in the ion must equal the charge on the ion

• Use Table E to check charges of polyatomic ions

Q.

What is the oxidation state of Cr in CrO42- ?

+6

+2

-2

+8

Q.

What is the oxidation number of Mn in MnO4- ?

-2

+2

+7

+8

Q.

What is oxidation number of P in K3PO4?

-2

-1

+1

+5

Q.

What is oxidation number of K in K3PO4?

-2

-1

+1

+5

Q.

What is the oxidation number of Cl in FeCl3?

-3

-1

+1

+3

Q.

What is the oxidation number of Fe in FeCl3?

-3

-2

+2

+3

Q.

What is the oxidation state of H in H2?

0

+1

-1

-2

Q.

How are you feeling with oxidation states as of now? 