Half Reactions: Balancing, H2O, H+, OH- 1. Write the oxidation half reaction and

Question

Half Reactions: Balancing, H2O, H+, OH-

1. Write the oxidation half reaction and the reduction half reaction for each electron-transfer reaction

a. Ag+(aq) + Fe2+(aq) -----> Ag(s) + Fe3+(aq)

b. 3Cr3+(aq) + Cr(s) -----> 3Cr2+(aq) + Cr3+(aq)

c. Mg(s) + Br2(l) -----> Mg2+(aq) + 2Br-(aq)

2. When the following half reaction is balanced under acidic conditions, what are the coeffieicents of each species shown?

a. HAsO2 +  H2O ----> H3AsO4 +  H+
In the above half reaction, the oxidation state of arsenic changes from___ to ___

b. HClO +  H+ -----> Cl2 +  H2O
In the above half reaction, the oxidation state of chlorine changes from __ to __

c. H2SO3 +  H2O ----->  SO42- +  H+
In the above half reaction, the oxidation state of sulfur changes from ___ to ___

3. When the following half reaction is balanced under basic conditions, what are the coefficients of each species shown?

a. Pb +  OH- ----->  HPbO2- +  H2O
In the above half reaction, the oxidation state of lead changes from ___ to ___

b. NO3- +  H2O ------>  NO2- +  OH-
In the above half reaction, the oxidation state of nitrogen changes from ___ to ___

c. Ni(OH)2 +  OH- ------>  NiO2 +  H2O
In the above half reaction, the oxidation state of nickel changes from ___ to ___

4. The following skeletal oxidation-reduction reaction occurs under acidic conditions. Write either the balanced oxidation half reaction or the reduction half reaction for each,

a. Oxidation half reaction: Hg + Pb2+ ------> Hg2+ + Pb

b. Reduction half reaction: Cu+ + Cr2O72- -------> Cu2+ + Cr3+

c. Reduction half reaction:

5. Identify each of the following half-reactions as either oxidation half-reaction or a reduction half-reaction. Then write a balanced equation for the overall redox reaction. Use smallest possible integer coefficients.

a.

b.

c.

Explanation / Answer

1.

(a)

Oxidation half reaction:

Fe2+ (aq.) -----------> Fe3+ (aq.) + e-

Reduction half reaction :

Ag+ (aq.) + e- -----------> Ag (s)

(b)

Oxidation half reaction :

Cr (s) -----------> Cr3+ (aq.) + 3 e-

Reduction half reaction :

Cr3+ (aq.) + e- ------------> Cr2+ (aq.)

(c)

Oxidation half reaction :
Mg (s) ----------> Mg2+ (aq.) + 2 e-

Reduction half reaction :

Br2 (l) + 2 e- -----------> 2 Br- (aq.)

2.

a. HAsO2 + 2 H2O ----> H3AsO4 + 2 H+ + 2 e-

Oxidation state of As changes from + 3 to + 5

b. 2 HClO + 2 H+ + 2 e- -----> Cl2 + 2 H2O

Oxidation state of Cl changes from + 1 to 0

c. H2SO3 +  H2O ----->  SO42- + 4 H+ + 2 e-

Oxidation state of S changes from + 4 to + 6

3.

a. Pb + 3 OH- ----->  HPbO2- +  H2O + 2 e-

Oxidation state of Pb changes from 0 to +2

b. NO3- +  H2O + 2 e- ------>  NO2- + 2 OH-

Oxidation state of N changes from + 5 to + 3

c. Ni(OH)2 + 2 OH- ------>  NiO2 + 2 H2O + 2 e-

Oxidation state of Ni changes from + 2 to + 4

4.

(a) Oxidation Half Reaction : Hg ----------> Hg2+ + 2 e-

(b) Reduction half reaction : Cr2O72- + 14 H+ + 6 e- ----------> 2 Cr3+ + 7 H2O

(c) Reduction Half reaction : ClO4- + 2 H+ + 2 e- ---------> ClO3- + H2O

5.

(a) Oxidation half reaction :

Pb (s) ----------> Pb2+ (aq.) + 2 e-

Reduction half reaction :
Br2 (l) + 2 e- ------------> 2 Br- (aq.)

(b)

Oxidation half reaction :

Co (s) ---------> Co2+ (aq.) + 2 e-

Reduction half reaction :

F2 (g) + 2 e- --------> 2 F- (aq.)
(c)
Oxidation half reaction :

Mg (s) ------------> Mg2+ (aq.) 2 e-

Reduction half reaction :

2 H+ (aq.) + 2 e- ----------> H2 (g)

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