Exam 6: Oxidation-Reduction Reactions

The reaction, HCl(aq)+ Na₂CO₃(aq) $\rarr$ NaCl(aq)+ H₂O(l)+ CO₂(g), involves changes in oxidation number and is therefore classified as a redox reaction.

Which substance in the reaction BrO₃^-(aq)+ 3 Zn(s)+ 6 H⁺(aq)→ Br^-(aq)+ 3 Zn²⁺(aq)+ 3 H₂O(l)is the oxidizing agent?

A student working on her research project will do a synthesis which involves bubbling chlorine gas through the aqueous reaction mixture in a closed system. The outlet from the system goes through a scrubber, which contains some sodium thiosulfate solution. The sodium thiosulfate will react with the chlorine passing through the scrubber to produce harmless chloride ion and sulfate ion. This prevents the chlorine from going up the exhaust system and polluting the atmosphere on campus grounds. The reaction is: Cl₂(g)+ S₂O₃^2-(aq)→ SO₄^2-(aq)+ Cl^-(aq)The reaction calls for 15.5 grams of chlorine gas. The student wants enough thiosulfate in the scrubber to be able to handle twice this amount to be on the safe side. How many grams of crystal sodium thiosulfate (which is actually sodium thiosulfate pentahydrate)should the student weigh out for use in the scrubber? Hint: Make sure you balance the equation and focus on units.

Which of the following involves oxidation?

Is the following, NO₃ → NO, an oxidation or a reduction half-reaction?

The oxidation number of N in NO₂ is ________.

When the carbohydrate, C₁₂H₂₂O₁₁, undergoes complete combustion, the reducing agent in the reaction is

A partial activity series is: Au < Ag < Cu < H₂ < Sn < Cd < Fe < Mn. Which metal(s)is/are NOT likely to be produced when each of the following compounds is made to react with Cd metal:Cd(NO₃)₂(aq); Fe(NO₃)₂(aq); HNO₃(aq); Cu(NO₃)₂(aq); Sn(NO₃)₂(aq); AgNO₃(aq)? Hint: In the partial activity series above, Mn is the most reactive and Au is the least reactive.

In the equation, CrO₄^2-(aq) + H₂O(l) $\rarr$ CrO₂^-(aq)+ OH^-(aq), the change in the oxidation number of the chromium atom is

Which statement is true concerning an oxidation-reduction reaction?

After balancing the following equation for the reaction in basic media, H₂O + CrO₄^2-(aq)+ Br^-(aq) $\rarr$ CrO₂^-(aq)+ BrO₃^-(aq)+ OH^- what is the sum of ALL the coefficients in the equation? (Remember to include values of 1 in your summation.)Hint: Start by balancing each half-reaction.

Fe²⁺(aq)reacts with MnO₄^-(aq)ion in acidic solution to yield Fe³⁺(aq)ions and Mn²⁺(aq)ions. 5Fe²⁺(aq)+ MnO₄^-(aq)+ 8H⁺ $\rarr$ 5Fe³⁺(aq)+ Mn²⁺(aq)+ 4H₂O Melanterite is a greenish mineral, and can be found on the walls of mines. A sample of melanterite, FeSO₄·7H₂O, was analyzed for purity using this reaction by titration of an aqueous solution of the sample. One such sample required 56.15 mL of 0.01301 M permanganate solution to completely titrate all the iron in the sample by the reaction shown above. How much did the sample weigh, if it was in fact pure melanterite? Hint: Watch your units carefully at each step of the problem.

Balance the redox reaction below in acidic solution.PbO₂(s)+ I^-(aq)→ Pb²⁺(aq)+ I₂(s)When balanced, what is the sum of all the coefficients? Hint: Do not neglect to include electrons when balancing redox reactions.

A solution was made by taking 2.500 g of KMnO₄ and dissolving it in enough water to make 1.000 liter of solution. This solution was used to titrate H₂C₂O₄·2H₂O, a very pure substance. In acidic media, the reaction is How many mL of this solution are required to titrate a 0.480 g sample of H₂C₂O₄·2H₂O? Hint: Remember to use moles as an intermediary when performing your stoichiometry calculations for the titration.

When hydrocarbons or coal contain sulfur what is formed during the complete combustion? Hint: Consider the products of a complete combustion reaction with something containing sulfur. What should always be produced?

A partial activity series is: Pb < Sn < Co < Fe < Zn. Which metal will react least readily with nonoxidizing acids to produce hydrogen gas? Hint: Oxidation is a loss of electrons.

What is the change in the oxidation number of manganese in the following? KMnO₄ $\rarr$ MnSO₄

Complete the balancing of the following half-reaction, taking place in basic media. How many electrons are needed to balance the half-reaction? Cr(OH)₄(aq) $\rarr$ CrO₄²(aq)Hint: Remember the coefficients when balancing half-reactions and look carefully at the oxidation numbers.

In the equation, 2H⁺ (aq)+ Zn(s) $\rarr$ H₂(g)+ Zn²⁺(aq), the H⁺ is the oxidizing agent and Zn is the reducing agent.

SO₂ is a dangerous air pollutant, which can harm human lungs. The quantity of SO₂ in air can be determined by the reaction, 2 MnO₄^-(aq)+ 5 SO₂(g)+ 2 H₂O $\rarr$ 5 SO₄^2-(aq)+ 2 Mn²⁺(aq)+ 4 H⁺ It required 185 mL of 0.0200 M MnO₄^-(aq)solution to completely react with all of the SO₂ in a sample of air. How many grams of SO₂ were in the sample?