18. In the reaction: 6 Mn²+ + 5 Cr2O7²- + 22 H+ →→→→ 11 H₂O + 10 Cr³+ + 6 MnO4 Which one of the following statements is true? a. Mn2+ is the free agent in excess. b. The oxidation number of Cr changes from +6 to +3. c. The oxidation number of Cr changes from -2 to +3. d. The oxidation number of Mn changes from +2 to +5. e. The oxidation number of Mn changes from 0 to +7.

. In each of the following reactions, identify which element is oxidized and which is reduced by assigning oxidation states. a.2Br2O3(s)+6Cl2(g)4BCl3(l)+3O2(g)b.GeH4(g)+O2(g)Ge(s)+2H2O(g)c.C2H4(g)+Cl2(g)C2H4Cl2(l)d.O2(g)+2F2(g)2OF2(g)

The Ostwald process for the commercial production of nitric acid involves the Following three steps: 4NH3(g)+5O2(g)4NO(g)+6H2O(s)2NO(g)+O2(g)2NO2(g)3NO2(g)+H2O(l)2HNO3(aq)+NO(g) a. Which reaction in the Ostwald process are oxidation-reduction reactions? b. Identify each oxidizing agent and reducing agent.

Chromium has been investigated as a coating for steel cans. The thickness of the chromium film is determined by dissolving a sample of a can in acid and oxidizing the resulting Cr3+ to Cr2O72 with the peroxydisulfate ion: S2O82(aq) + Cr3+(aq) + H2O(l) Cr2O72(aq) + SO42(aq) + H+(aq) (Unbalanced) After removal of unreacted S2O82 an excess of ferrous ammonium sulfate [Fe(NH4)2(SO4)26H2O] is added, reacting with Cr2O72 produced from the first reaction. The unreacted Fe2+ from the excess ferrous ammonium sulfate is titrated with a separate K2Cr2O7 solution. The reaction is: H+(aq) + Fe2+(aq) + Cr2O72(aq) Fe3+(aq) + Cr3+(aq) + H2O(l) (Unbalanced) a. Write balanced chemical equations for the two reactions. b. In one analysis, a 40.0-cm2 sample of a chromium-plated can was treated according to this procedure. After dissolution and removal of excess S2O82, 3.000 g of Fe(NH4)2(SO4)26H2O was added. It took 8.58 mL of 0.0520 M K2Cr2O7 solution to completely react with the excess Fe2+. Calculate the thickness of the chromium film on the can. (The density of chromium is 7.19 g/cm3)