300 Chemistry Problems

300 Chemistry Problems

Redox & Electrochemistry

1. Definitions:

a. Oxidation =

b. Reduction =

c. Oxidizing agent =

d. Reducing agent =

2. Assign an oxidation state to each atom in the following.

a. Au

b. H2O

c. Mg2+

d. K2O

e. BF3

f. NH4+

g. Ca(OH)2

h. S2O7

i. Fe2(CO3)3

j. NaBiO3

k. NaHCO3

l. Cr2O72-

m. NH4NO3

n. H2PO4-

o. K2CrO4

p. NaNO3

q. NH3

r. ZnO

s. CaH2

t. CO2

u. N2

v. Na2SO4

w. K2SO3

x. Al(OH)3

y. Mg3(PO4)2

z. HNO3

3. Determine whether each of the following reactions is a redox reaction or not. For the ones that are redox reactions, identify which elements are changing in oxidation state.

a. Na2S + FeCl2 → 2 NaCl + FeS

b. 2 Na + 2 H2O → 2 NaOH + H2

c. 2 KClO3 → 2 KCl + 3 O2

d. SO2 + H2O → H2SO3

e. 2 Al + 6 HCl → 2 AlCl3 + 3 H2

f. CH4 + 2O2 → CO2 + 2 H2O

g. AgNO3 + NaCl → AgCl + NaNO3

h. AgNO3 + Cu → CuNO3 + Ag

4. For each of the following reactions, identify which element is being oxidized and which element is being reduced. Be specific as you identify them (i.e., “the chromium in the chromate ion is being reduced).

a. CuO + H2 → Cu + H2O

b. CH4 + 2 O2 → CO2 + 2 H2O

c. 2 Na + Br2 → 2 NaBr

d. Ca + H2O → CaO + H2

e. 2 H2 + O2 → 2 H2O

f. 4 HCl + O2 → 2 H2O + 2 Cl2

g. 4 Al + 3 O2 → 2 Al2O3

h. Fe + SnCl2 → FeCl2 + Sn

5. For each of the following reactions, identify which element is being oxidized and which element is being reduced. Be specific, as you did in #4. Describe the change in oxidation state of the two elements and the number of electrons being gained or lost (i.e., “silver metal is losing 1 electron to go from an oxidation state of 0 to +1”). Then, identify the oxidizing agent and reducing agent (i.e., silver metal is oxidized, so it is the reducing agent).

a. PbO2 + 4 HI → I2 + PbI2 + 2 H2O

b. P4 + 5 O2 → P4O10

c. SnCl2 + 2 FeCl3 → 2 FeCl2 + SnCl4

d. 2 Na + FeCl2 → 2 NaCl + Fe

e. 2 C2H2 + 5 O2 → 4 CO2 + 2 H2O

f. 2 PbS + 3 O2 → 2 SO2 + 2 PbO

g. 2 H2 + O2 → 2 H2O

h. Cu + HNO3 → CuNO3 + H2

i. AgNO3 + Cu → CuNO3 + Ag

6. Write and balance a half reaction for each of the following:

a. Oxidation of magnesium metal to magnesium ion

b. Oxidation of chloride ion to chlorine gas

c. Oxidation of copper metal to copper(I) ion

d. Oxidation of bromide ion to bromine liquid

e. Reduction of hydrogen ion to hydrogen gas

f. Reduction of oxygen gas to oxide ion

g. Reduction of aluminum ion to aluminum metal

h. Reduction of manganese(VII) ion to manganese(II) ion

7. For each reaction, write out and balance the two half reactions, then make the number of electrons transferred equal (by multiplying if necessary), and add the half reactions to get the balanced, overall equation. Remember to double check your overall reactions to make sure they are balanced for mass and charge.

a. Na + N2 → Na+ + N3-

b. Mg + Cl2 → Mg2+ + Cl-

c. Al + Br2 → Al3+ + Br-

d. Fe + O2 → Fe3+ + O2-

e. Mg + Br2 → Mg2+ + Br-

f. Na + S → Na+ + S2-

g. Cl2 + Br- → Br2 + Cl-

h. K + N2 → K+ + N3-

8. Balance the following skeleton reactions in acidic solution.

a. ClO3- + I- → I2 + Cl-

b. MnO4- + H2O2 → Mn2+ + O2

c. Cr2O72- + Zn → Zn2+ + Cr3+

d. CrO42- + N2O → Cr3+ + NO

e. Sb + NO3- → Sb4O6 + NO

f. Mn2+ + BiO3- → MnO4- + Bi3+

g. H2S + NO3- → S8 + NO

h. As4O6 + MnO4- → AsO43- + Mn2+

i. I- + ClO- → I3- + Cl-

j. As2O3 + NO3- → H3AsO4 + NO

k. Br- + MnO4- → Br2 + Mn2+

l. P4 + Cr2O72- → H3PO4 + Cr3+

9. Balance the following skeleton reactions in basic solution.

a. MnO4- + SO32- → MnO2 + SO42-

b. AsO43- + NO2- → AsO2- + NO3-

c. BH4- + ClO3- → H2BO3- + Cl-

d. Br2 → BrO3- + Br-

e. MnO4- + CN- → MnO2 + CNO-

f. SO32- + Cl2 → SO42- + Cl-

g. NO2- + Al → NH3 + AlO2-

h. MnO4- + S2- → MnO2 + SO32-

i. Cl2 + Br2 → OBr- + Cl-

j. S8 + MnO4- → SO42- + MnO2

For additional practice:

Relevant sections in textbook are all sections in Chapter 18 except sections 18.6, 18.7, and 18.8

Practice problems are p. 602-604 (1-27)