Redox

Redox Problem Set 1: Reactions and Stoichiometry
(All of these questions are no calculator friendly) 1) Give the oxidation number of carbon in each of the following: a) b) c) d) CF2Cl2 Na2C2O4 HCO3-1 C2H6

2) Give the oxidation number of sulphur in each of the following: a) b) c) d) SOCl2 H2S2 H2SO3 Na2S

3) Identify the oxidizing and reducing agents in each of the following: a) b) c) d) 8H+(aq) + 6Cl-1(aq) + Sn(s) + 4NO3-1(aq) SnCl6 -2(aq) + 4NO2(g) + 4H2O(l) 2MnO4-1(aq) + 10Cl-1(aq) + 16H+(aq) 5Cl2(g) + 2Mn+2(aq) + 8H2O(l) + -2 -2 8H (aq) + Cr2O7 (aq) + 3SO3 (aq) 2Cr+3(aq) + 3SO4-2(aq) + 4H2O(l) NO3-1(aq) + 4Zn(s) + 7OH-1(aq) + 6H2O(l) 4Zn(OH)4-2(aq) + NH3(aq)

4) Balance the following oxidation-reduction equations. All reactions occur in acidic solutions. a) b) c) d) Zn + NO3-1 ReO2 + Cl2 HNO2 + MnO4-1 Cu + NO3-1 Zn2+ + NH4+ HReO4 + Cl-1 NO3-1 + Mn2+ 2+ Cu + NO

5) Balance the following oxidation-reduction equations. All reactions occur in basic solutions. a) b) c) d) S2O3-2 + OCl-1 SO4-2 + Cl-1 NiO2 + Fe Ni(OH)2 + Fe(OH)3 SbH3 + H2O Sb(OH)4-1 + H2 P4 PH3 + HPO3-2

6) Balance the folowing oxidation-reduction equations under the specific conditions noted: a) Pb + PbO2 + SO4-2 PbSO4 (acidic solution) -2 b) CrI3 + Cl2 CrO4 + IO4-1 + Cl-1 (basic solution) c) XO2+ + YO+ X2O4-3 + Y-1 + Y3O7-2 (basic solution) 7) Given the following unbalanced oxidation-reduction reaction that occurs in basic solution: S2O3-2(aq) + H2O2(aq) a) b) c) d) S3O6-2(aq) + SO4-2(aq) + H2O(l)

Balance the reaction. Which substance is the oxidizing agent? What is the equivalent weight of H2O2 (Molar mass = 34.0 grams) in the above reaction? What is the normality of a 0.040 M H2O2 solution used in the above reaction?

8) Iodine reacts with thiosulphate ion (S2O3-2) in acidic solution to form iodide and tetrathionate ion (S4O6-2). Calculate the volume in mL of 0.100 M Na2S2O3 needed to react with 0.2538 g of I2. (Answer = 20.00 mL)

9) Thyroxine (C15H11I4NO4) is a hormone synthesized by the thyroid gland and used to control many metabolic functions in the body. A physiologist determines the mass percentage of thyroxine in a thyroid extract by igniting 0.7768 grams of extract with sodium carbonate, which converts the iodine to iodide. The iodide is dissolved in water, and bromine and hydrochloric acid are added, which converts the iodine to iodate. a) How many moles of iodate form per mole of thyroxine? b) Excess bromine is boiled off and more iodide is added, which reacts as shown in the following unbalanced equation: IO3-1(aq) + H+(aq) + I-1(aq) I2(aq) + H2O(l)

How many moles of iodine are produced per mole of thyroxine? (Hint: Be sure to balance the charges as well as the atoms.) What are the oxidizing and reducing reagents in the reaction? c) The iodine reacts completely with 24.00 mL of 0.1000 M thiosulphate as shown in the following unbalanced equation: I2(aq) + S2O3-2(aq) I-1(aq) + S4O6-2(aq)

What is the mass percent of thyroxine in the thyroid extract? Do this part of the question by using normality, molarity and equivalents. DO NOT balance any redox equation to solve this part of the problem. (Answer = 10.00%)