Complete and balance the following equations, and identify the oxidizing and red

Question

Complete and balance the following equations, and identify the oxidizing and reducing agents. (Use the lowest possible coefficients. Include states-of-matter (s), (l), (g), (aq) similar to the given reaction.)

(a)    H2O2(aq) + Cl2O7(aq) ? ClO2-(aq) + O2(g) (basic solution). (Identify balance equation and identify oxidizing and reducing agents)

(b)    Tl2O3(s) + NH2OH(aq) ? TlOH(s) + N2(g) (basic solution). (Identify balance equation and identify oxidizing and reducing agents)

(c)    MnO4-(aq) + Br-(aq) ? MnO2(s) + BrO3-(aq) (basic solution).  (Identify balance equation and identify oxidizing and reducing agents)

(d)    Pb(OH)42-(aq) + ClO-(aq) ? PbO2(s) + Cl-(aq) (basic solution). (Identify balance equation and identify oxidizing and reducing agents)

Explanation / Answer

a)

H2O2, the O2 charge increases, so it is the reducing agent. ClO2 is the oxidizing agent.

2OH(-) + Cl2O7 + 4H2O2 -> 2ClO2(-) + 5H2O + 4O2
Cl2O7 is oxidizing agent
H2O2 is reducing agent

b)

oxidizing agent -> ti2o3

reducing agent -> nh2oh.

Tl2O3 (s) + 4 NH2OH (aq) ? 2 TlOH (s) + 2 N2 (g) + 5 H2O (l),base
Tl is reduced, Nis oxidized

c)

MnO4- + 4 H+ + 3e- = MnO2 + 2 H2O
Br- + 3 H2O = BrO3- + 6 H+ + 6e-

2 MnO4- + Br- + 2 H+ = MnO2 + BrO3- + H2O

add 2 OH- on the left and on the right ( 2 OH- + 2 H+ = 2 H2O)

2 MnO4- + Br- + H2O = MnO2 + BrO3- + 2 OH-

MnO4- is the oxidizing agent
Br- is the reducing agent

d)

Step 1: Determine which atoms have had their oxidation number changed as they changed from a reactant to a product.
H is +1 unless it is in a metallic hydride. In a metallic hydride, H is -1. O is -2 unless the compound is peroxide. In a peroxide O is -1.
The sum of the oxidation numbers in an ion must equal the charge of the ion. The sum of the oxidation numbers in an ion must equal the charge of the molecule must equal 0.

In Pb(OH)4 2-, OH = -1, 4 (OH) = -4
Pb + -4 = -2, Pb = +2
In ClO-, O = -2
Cl + -2 = -1, Cl = +3
In PbO2, Pb = +4
Cl = -1
The oxidation number of Pb increased from +2 to +4. The oxidation number of Cl decreased from +3 to -1.

Step 2: Write the skeletons of the oxidation and reduction half-reactions. (The skeleton reactions contain the formulas of the compounds oxidized and reduced, but the atoms and electrons have not yet been balanced.)

Oxidation reaction: Pb(OH)4 2- ? PbO2
Reduction reaction: ClO- ? Cl-

Step 3: Balance all elements other than H and O.
Pb and Cl are balanced.

Step 4: Balance the oxygen atoms by adding H2O molecules where needed.
In the oxidation reaction, we need 2 O

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