Redox Rules: All the Examples and Problems
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Twenty Examples

Example #1: What is the oxidation state of Cl in HCl?

Example #2: What is the oxidation state of Na in Na2O?

Example #3: What is the oxidation state of Cl in ClO¯?

Example #4: What is the oxidation state of Cl in ClO2¯?

Example #5: What is the oxidation state of Cl in ClO3¯?

Example #6: What is the oxidation state of Cl in ClO4¯?

Example #7: What is the oxidation state of S in SO42¯?

Example #8: What is the oxidation state of S in SO32¯?

Example #9: What are the oxidation states in KCl?

Example #10: What is the oxidation state for each element in NaMnO4?

Example #11: What is the oxidation state of N and of P in NH4H2PO4?

Example #12: For H2O2, is the oxidation state for O2, −2 or −4?

Example #13: For Fe3O4, is the oxidation state for O4, −2 or −8?

Example #14: Determine the oxidation state for I in I3¯.

Example #15: What is the oxidation state of silver in Ag2F (silver subfluoride)?

Example #16: What is the oxidation state of tungsten in tungsten disulfide, WS2?

Example #17: What is the oxidation state of manganese in LiMnO2?

Example #18: Give the oxidation states of the elements in the following compounds.

(a) ClO2    (b) XeF2    (c) CO    (d) OF2    (e) O2F2    (f) Bi2O5    (g) MnO2    (h) Mn2O4

Example #19: What is the oxidation state of each of the following:

(a) Se in SeO32¯     (b) I in H5IO6     (c) S in Al2(SO3)3     (d) N and C in HCN    (e) Cu in Na3[CuCl5]

Example #20: Find the oxidation state of chlorine in:

(a) ClO    (e) ClF5    (i) Cl2O2 (chlorine peroxide)
(b) ClO2    (f) ClOF3    (j) Cl2O4 (chlorine perchlorate)
(c) ClF    (g) Cl2O6    (k) ClN3
(d) ClF3    (h) Cl2O7    (ℓ) Cl2

Bonus Example: Find the oxidation state of nitrogen in:

(a) NO3¯    (e) N2O    (i) N2O4
(b) N2H4    (f) NO    (j) N2O3
(c) NO2+    (g) NO2¯    (k) N3¯
(d) N2O5    (h) NO2    (ℓ) N2

Problems 1-10

Problem #1: What is the oxidation state of carbon in calcium oxalate?

Problem #2: C in CO32¯

Problem #3: Cr in CrO42¯

Problem #4: Cr in Cr2O72¯

Problem #5: Fe in Fe2O3

Problem #6: Pb in PbOH+

Problem #7: V in VO2+

Problem #8: V in VO2+

Problem #9: Mn in MnO4¯

Problem #10: Mn in MnO42¯

Bonus Problem: What is the oxidation state of Re in potassium nonahydridorhenate, which has the formula K2ReH9


Problems 11-30

Hydrides are compounds of a metal and hydrogen. What are the oxidation states of the elements present in each formula given in 11-13?

Problem #11: NaH

Problem #12: CaH2

Problem #13: SH6

Peroxides have the polyatomic ion O22¯ present. Two problems:

Problem #14: H2O2

Problem #15: CaO2

Problem #16: HIO3, the iodine has an oxidation state of:

Problem #17: S2O32¯, thiosulfate:

Problem #18: What is the oxidation state of all free elements? Another way to ask this is to say that the elements are in their uncombined state.

Problem #19: Determine the oxidation state of P in P2O5.

Problem #20: Determine the oxidation state of S in Al2S3.

Problem #21: Determine the oxidation state of Te in Sc2Te3.

Problem #22: Determine the oxidation state of Si in SiF62¯.

Problem #23: All monatomic ions have oxidation states equal to the ______.

(a) difference of protons and electrons
(b) number of protons
(c) number of electrons
(d) difference of protons and neutrons

Problem #24: On rare occasions, oxidation states do not have to be whole numbers. Determine the oxidation state for S in S4O62¯.

Problem #25: What are the oxidation states for each Mn in Mn3O4? For each Fe in Fe3O4?

Problem #26: In which compound does hydrogen have an oxidation state of −1?

(a) NH3
(b) KH
(c) HCl
(d) H2O

Problem #27: In which compound does oxygen have an oxidation state of −1?

(a) O2
(b) H2O2
(c) H2O
(d) OF2
(e) KO2

Problem #28: Superoxide is not commonly mentioned in introductory chemistry classes. It is the polyatomic ion O2¯. KO2 is the most well-known of the superoxides. What are the oxidation states on each oxygen in the superoxide anion?

Problem #29: Some chemical compounds have one (or more) atoms in them where the oxidation state is zero. An example of this is glucose, C6H12O6.

Problem #30: What is the oxidation state of P in HPO42¯?

Bonus Problem: What is the oxidation state and coordination number of rhodium in the coordination compound K[RhCl(OH)(C2O4)2] 6H2O?


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