Question

1. Complete the following sentences:

(a) Oxidation is a gain of electrons OR an increase in oxidation state
(b) Reduction is a loss of electrons OR a decrease in oxidation state
(c) Redox reactions involve a transfer of electrons from the element being _______________ to the element being ________________.

2. Complete the rules for assigning oxidation numbers by filling in the missing words.
(1) The oxidation number of an element is .
(2) The oxidation number of a monatomic ion is equal to the of the ion.
(3) In a polyatomic ion, the oxidation numbers of all the atoms in the ion add up to the
of the ion.
(4) In a compound, the sum of all the oxidation numbers of the atoms is
(5) The oxidation number of oxygen in its ions and compounds is always
except in where it is -1.
(6) The oxidation number of hydrogen in its ions and compounds is always
(7) The oxidation number of elements in compounds is often the same as their __________ if they were an ion

3. Give the oxidation number of the bold species in each of the following substances.

H2O S8 H2O2
AlCl3 O3 Fe2O3
MnO2 Cu KMnO4



4. Give the oxidation number of the bold species in each of the following substances.

Br- S2O32- NH4+
H2S MnO4- Cr3+
O22- Cr2O72- I-
C2O42- NO3- OCl-
SO42- MnO2 SO2
.

5. State the oxidation number of the underlined element in each of the following species.
(a) HCl (j) FeSO4
(b) CO2 (k) Fe2(CO3)3
(c) SO32- (l) KMnO4
(d) CO (m) MnI2
(e) KI (n) CaO
(f) H2O2 (o) Cr2O72-
(g) Cr(NO3)3 (p) HSO3-
(h) Br2 (q) ZnO
(i) H2SO4 (r) H2O

6. State whether each of the following reactions is an oxidation or a reduction reaction. Justify.
(a) O2- → O2
(b) I2 → I-
(c) Mg2+ → Mg
(d) HSO3- → SO42-
(e) Fe3+ → Fe2+
(f) Br2 → Br-
(g) Cr2O72- → Cr3+
(h) MnO4- → Mn2+
(i) Cl2 → Cl-
(j) H+ → H2

Answer 1

Oxidation is a gain of electrons or an increase in oxidation state, while reduction is a loss of electrons or a decrease in oxidation state. Redox reactions involve a transfer of electrons. Rules for assigning oxidation numbers are provided along with examples of oxidation numbers for various substances.

Step-by-step explanation:

Oxidation is a gain of electrons or an increase in oxidation state. Reduction is a loss of electrons or a decrease in oxidation state. Redox reactions involve a transfer of electrons from the element being oxidized to the element being reduced.

1. The oxidation number of an element is zero.
2. The oxidation number of a monatomic ion is equal to the charge of the ion.
3. In a polyatomic ion, the oxidation numbers of all the atoms in the ion add up to the charge of the ion.
4. In a compound, the sum of all the oxidation numbers of the atoms is zero.
5. The oxidation number of oxygen in its ions and compounds is always -2, except in peroxides where it is -1.
6. The oxidation number of hydrogen in its ions and compounds is always +1.
7. The oxidation number of elements in compounds is often the same as their charge if they were an ion.

3. Give the oxidation number of the bold species in each of the following substances:
H2O (-2), S8 (0), H2O2 (-1), AlCl3 (+3), O3 (0), Fe2O3 (+3), MnO2 (+4), Cu (0), KMnO4 (+7)

4. Give the oxidation number of the bold species in each of the following substances:
Br- (-1), S2O32- (+4), NH4+ (+1), H2S (-2), MnO4- (+7), Cr3+ (+3), O22- (-2), Cr2O72- (+6), I- (-1), C2O42- (+3), NO3- (-1), OCl- (+1), SO42- (+6), MnO2 (+4), SO2 (0)

5. State the oxidation number of the underlined element in each of the following species:
(a) HCl: H (+1), Cl (-1); (j) FeSO4: Fe (+2), S (+6), O (-2); (b) CO2: C (+4), O (-2); (k) Fe2(CO3)3: Fe (+3), C (+4), O (-2); (c) SO32-: S (+4), O (-2); (l) KMnO4: K (+1), Mn (+7), O (-2); (d) CO: C (+2), O (-2); (m) MnI2: Mn (+2), I (-1); (e) KI: K (+1), I (-1); (n) CaO: Ca (+2), O (-2); (f) H2O2: H (+1), O (-1); (o) Cr2O72-: Cr (+6), O (-2); (g) Cr(NO3)3: Cr (+3), N (+5), O (-2); (p) HSO3-: H (+1), S (+4), O (-2); (h) Br2: Br (0); (q) ZnO: Zn (+2), O (-2); (i) H2SO4: H (+1), S (+6), O (-2); (r) H2O: H (+1), O (-2)

6. State whether each of the following reactions is an oxidation or a reduction reaction. Justify.
(a) O2- → O2: reduction - O2- is gaining electrons to form O2; (b) I2 → I-: reduction - I2 is gaining electrons to form I-; (c) Mg2+ → Mg: oxidation - Mg2+ is losing electrons to form Mg; (d) HSO3- → SO42-: oxidation - HSO3- is losing electrons to form SO42-; (e) Fe3+ → Fe2+: reduction - Fe3+ is gaining electrons to form Fe2+; (f) Br2 → Br-: reduction - Br2 is gaining electrons to form Br-; (g) Cr2O72- → Cr3+: reduction - Cr2O72- is gaining electrons to form Cr3+; (h) MnO4- → Mn2+: reduction - MnO4- is gaining electrons to form Mn2+; (i) Cl2 → Cl-: reduction - Cl2 is gaining electrons to form Cl-; (j) H+ → H2: reduction - H+ is gaining electrons to form H2.