Why is oxidation always coupled with reduction

Problem 1QP Match the key terms with the descriptions provided. (a) an electrochemical cell through which electric current is passed to cause a nonspontaneous oxidation-reduction reaction to occur (b) the electrode at which reduction occurs (c) a chemical process in which an atom increases in oxidation number (d) an oxidation or reduction process that occurs in one compartment of an electrochemical cell (e) the study of the relationship between chemical reactions and electrical work (f) a solid material that conducts electrical charge and is used as part of an electrochemical cell (g) an atom, ion, or molecule that causes an increase in the oxidation number of another substance (h) a reaction in which electrons are transferred (i) a slow deterioration of metals due to interaction with the environment (j) a charge assigned to the atoms in a compound according to a set of rules used in an electron accounting system

Problem 2QP Match the key terms with the descriptions provided. (a) an electrochemical cell in which an oxidationreduction reaction causes electrons to flow through an external circuit (b) the electrode at which oxidation occurs (c) a chemical process in which an atom decreases in oxidation number (d) an individual compartment in which either an oxidation or a reduction reaction occurs (e) one or more interconnected voltaic cells used as a portable source of electricity (f) a device used in electrochemical cells that allows migration of ions to maintain electrical neutrality but prevents mixing of the electrolyte solutions (g) an atom, ion, or molecule that causes a decrease in the oxidation number of another substance (h) a process in which an electric current forces a nonspontaneous oxidation-reduction reaction to occur (i) a chemical reaction or physical change that occurs without outside intervention

Problem 90QP A common error of amateur plumbers is to connect iron and copper pipes directly. The pipe eventually corrodes at the junction of the two metals if it is used with impure water or in moist soil. Which metal corrodes? Explain your answer.

Problem 3QP What is an oxidation-reduction reaction?

Problem 4QP Why is oxidation always coupled with reduction?

Problem 5QP How do you know when something is oxidized?

Problem 6QP How do you know when something is reduced?

Problem 7QP When a strip of magnesium metal is placed in an aqueous solution of copper(II) nitrate, elemental copper coats the surface of the magnesium strip and aqueous magnesium nitrate forms. (a) Write a balanced equation for this reaction. (b) What happens to the charge on magnesium as products form? How many electrons are transferred? Does magnesium gain or lose electrons? (c) What happens to the charge on copper as products form? How many electrons are transferred? Does copper gain or lose electrons?

Problem 8QP When a strip of nickel metal is placed in an aqueous solution of lead(II) nitrate, elemental lead coats the surface of the nickel strip and aqueous nickel(II) nitrate forms. (a) Write a balanced equation for this reaction. (b) What happens to the charge on nickel as products form? How many electrons are transferred? Does nickel gain or lose electrons? (c) What happens to the charge on lead as products form? How many electrons are transferred? Does lead gain or lose electrons?

Problem 9QP Consider the following reaction: (a) Which species is oxidized? (b) Which species is reduced? (c) What is the oxidizing agent? (d) What is the reducing agent? (e) Draw a molecular-level picture of what happens at the surface of the magnesium metal.

Problem 10QP Consider the following reaction: (a) Which species is oxidized? (b) Which species is reduced? (c) What is the oxidizing agent? (d) What is the reducing agent? (e) Draw a molecular-level picture of what happens at the surface of the manganese metal.

Problem 11QP What is an oxidation number?

Problem 12QP How do oxidation numbers change during oxidation and during reduction?

Problem 13QP Indicate the oxidation number of each element in the following species.

Problem 14QP Indicate the oxidation number of each element in the following species.

Problem 15QP What is the oxidation number of each atom in the compound represented by the following molecule?

Problem 16QP What is the oxidation number of each atom in the compound represented by the following molecule?

Problem 17QP What is the oxidation number of phosphorus in each of the following oxides?

Problem 18QP Determine the oxidation number of chlorine in each of these chlorine oxides.

Problem 19QP Indicate the oxidation number of phosphorus in each of the following compounds.

Problem 20QP Determine the oxidation number of iodine in each of the following compounds.

Problem 22QP The ion shown has a charge of 1–. What are the oxidation numbers of all of the atoms in this ion?

Problem 23QP Assign an oxidation number to bromine in each of the following compounds or ions.

Problem 26QP Determine the oxidation number of each element in the following compounds.

Problem 27QP Determine the oxidation number of each element in the following ions.

Problem 28QP Determine the oxidation number of each element in the following ions.

Problem 29QP Determine which of the following represent oxidation-reduction reactions. For reactions that involve xidation-reduction, determine the oxidizing and reducing agents.

Problem 25QP Determine the oxidation number of each element in the following compounds.

Problem 24QP Indicate the oxidation number of chromium in each of the following compounds.

Problem 31QP Under certain conditions, nitrogen gas reacts with oxygen gas to form nitrogen monoxide gas. (a) Write a balanced equation for this reaction. (b) What happens to the oxidation number of a nitrogen atom when it changes from a reactant to a product? How many electrons are transferred? Does nitrogen gain them or lose them? (c) What happens to the oxidation number of an oxygen atom when it changes from a reactant to a product? How many electrons are transferred? Does oxygen gain them or lose them?

Problem 32QP Under certain conditions, solid carbon reacts with oxygen gas to form carbon monoxide gas. (a) Write a balanced equation for this reaction. (b) What happens to the oxidation number of a carbon atom when it changes from a reactant to a product? How many electrons are transferred? Does carbon gain them or lose them? (c) What happens to the oxidation number of an oxygen atom when it changes from a reactant to a product? How many electrons are transferred? Does oxygen gain them or lose them?

Problem 33QP Consider the following reaction: (a) Which species is oxidized? (b) Which species is reduced? (c) What is the oxidizing agent? (d) What is the reducing agent?

Problem 30QP Determine which of the following represent oxidation-reduction reactions. For reactions that involve oxidation-reduction, determine the oxidizing and reducing agents.

Problem 34QP Consider the following reaction: (a) Which species is oxidized? (b) Which species is reduced? (c) What is the oxidizing agent? (d) What is the reducing agent?

Problem 35QP In the following oxidation-reduction reactions, identify the oxidizing agent, the reducing agent, and the number of electrons transferred.

Problem 36QP In the following oxidation-reduction reactions, identify the oxidizing agent, the reducing agent, and the number of electrons transferred.

Problem 37QP Draw a diagram of a voltaic cell that corresponds to the following reaction: Label all components of the cell, including the anode and the cathode. Identify the electrolyte solutions needed in each half-cell compartment. Write half-reactions to describe the processes that occur at each electrode.

Problem 38QP Draw a diagram of a voltaic cell that corresponds to the following reaction: Label all components of the cell, including the anode and the cathode. Identify the electrolyte solutions needed in each half-cell compartment. Write half-reactions to describe the processes that occur at each electrode.

Problem 39QP The figure shows a molecular-level representation for the iron-nickel cell described in Question 14.37 before the reaction begins. Draw a picture of what has happened at each electrode after the cell has run for a long time. Reference Question 14.37: Draw a diagram of a voltaic cell that corresponds to the following reaction: Label all components of the cell, including the anode and the cathode. Identify the electrolyte solutions needed in each half-cell compartment. Write half-reactions to describe the processes that occur at each electrode.

Problem 41QP The reaction that occurs in a lead-acid battery is as follows: What gets oxidized in this battery? What gets reduced? What is the oxidizing agent? What is the reducing agent?

Problem 42QP The reaction that occurs in a common dry cell battery is as follows: What gets oxidized in this battery? What gets reduced? What is the oxidizing agent? What is the reducing agent?

Problem 44QP The zinc-silver oxide battery, although expensive, is used to power satellite systems because of its light weight. Unbalanced half-reactions that occur in this battery are Which equation represents the oxidation half-reaction? Which represents the reduction half-reaction? Add electrons to the appropriate side of each equation to account for the change in oxidation number.

Problem 43QP The nickel-cadmium battery is used in portable appliances and power tools. Unbalanced half-reactions that occur in this battery are Which equation represents the oxidation half-reaction? Which represents the reduction half-reaction? Add electrons to the appropriate side of each equation to account for the change in oxidation number.

Problem 45QP Balance the following half-reactions.

Problem 40QP The figure shows a molecular-level representation for the magnesium-tin cell described in Question 14.38 before the reaction begins. Draw a picture of what has happened at each electrode after the cell has run for a long time. Reference Question 14.38: Draw a diagram of a voltaic cell that corresponds to the following reaction: Label all components of the cell, including the anode and the cathode. Identify the electrolyte solutions needed in each half-cell compartment. Write half-reactions to describe the processes that occur at each electrode.

Problem 46QP Balance the following half-reactions.

Problem 47QP For each of the following, write balanced half-reaction equations. Also write overall balanced equations.

Problem 48QP For each of the following, write balanced half-reaction equations. Also write overall balanced equations.

Problem 49QP Aqueous iron(III) sulfate reacts with aqueous potassium iodide to form aqueous iron(II) sulfate, aqueous potassium sulfate, and aqueous iodine molecules. Write a balanced equation for this oxidation-reduction reaction.

Problem 50QP When gaseous sulfur dioxide is bubbled into a nitric acid solution, sulfuric acid and gaseous nitrogen dioxide form. Write a balanced equation for this oxidation-reduction reaction.

Problem 51QP Balance the following half-reactions, adding H+(aq), H2O(l), and electrons as appropriate.

Problem 52QP Balance the following half-reactions, adding H+(aq), H2O(l), and electrons as appropriate.

Problem 53QP Balance the following half-reactions, adding OH–(aq), H2O(l), and electrons as appropriate.

Problem 54QP Balance the following half-reactions, adding OH–(aq), H2O(l), and electrons as appropriate.

Problem 55QP Complete and balance the following oxidation-reduction reactions, assuming they occur in acidic solution.

Problem 56QP Complete and balance the following oxidation-reduction reactions, assuming they occur in basic solution.

Problem 59QP Denitrification occurs when nitrogen in the soil is lost to the atmosphere. One way in which denitrification can occur in acidic soils rich in plant matter is described by the following equation: Balance this equation, adding H+(aq) and H2O(l) as necessary.

Problem 58QP Complete and balance the following oxidation-reduction reactions, assuming they occur in acidic solution.

Problem 57QP Complete and balance the following oxidation-reduction reactions, assuming they occur in basic solution.

Problem 60QP When iodine is oxidized in concentrated HNO3, it produces the white solid iodic acid, HIO3: Balance this equation, adding H+(aq) and H2O(l) as necessary.

Problem 61QP Consider the partially labeled voltaic cell shown. Suppose you want to deposit solid iron on the iron electrode. What might you use for the other electrode? What electrolyte would you put in the half-cell with that other electrode?

Problem 62QP Consider the partially labeled voltaic cell shown. Suppose you want to deposit solid tin on the tin electrode. What might you use for the other electrode? What electrolyte would you put in the half-cell with that other electrode?

Problem 63QP Using the activity series in Figure 14.22, place the following metals in order of increasing reducing strength. Reference Figure 14.22:

Problem 65QP What is electrolysis?

Problem 64QP Using the activity series in Figure 14.22, place the following metal ions in order of increasing oxidizing strength. Reference Figure 14.22:

Problem 66QP Describe what happens at each electrode during the electrolysis of molten sodium chloride.

Problem 67QP In the electrolysis of molten sodium iodide, liquid sodium and iodine gas are produced. Consider the following diagram: (a) When the power is turned on, what happens at the cathode? (b) When the power is turned on, what happens at the anode? (c) Write oxidation and reduction half-reactions. (d) Write an overall equation for the reaction.

Problem 68QP In the electrolysis of molten aluminum chloride, liquid aluminum and chlorine gas are produced. Consider the following diagram: (a) When the power is turned on, what happens at the cathode? (b) When the power is turned on, what happens at the anode? (c) Write oxidation and reduction half-reactions. (d) Write an overall equation for the reaction.

Problem 69QP For Question 14.67, draw molecular-level pictures to represent what happens at the anode and cathode. Reference Question 14.67: In the electrolysis of molten sodium iodide, liquid sodium and iodine gas are produced. Consider the following diagram: (a) When the power is turned on, what happens at the cathode? (b) When the power is turned on, what happens at the anode? (c) Write oxidation and reduction half-reactions. (d) Write an overall equation for the reaction.

Problem 70QP For Question 14.68, draw molecular-level pictures to represent what happens at the anode and cathode. Reference Question 14.68: In the electrolysis of molten aluminum chloride, liquid aluminum and chlorine gas are produced. Consider the following diagram: (a) When the power is turned on, what happens at the cathode? (b) When the power is turned on, what happens at the anode? (c) Write oxidation and reduction half-reactions. (d) Write an overall equation for the reaction.

Problem 71QP How does attaching a piece of magnesium to the steel hull of a ship prevent the hull from corroding?

Problem 72QP How does zinc attached to an iron pipe prevent the pipe from corroding?

Problem 73QP Iron is often covered with tin, as in a tin can, to protect it from corrosion. If the tin coating is scratched and some iron is exposed, however, the iron corrodes very rapidly. Explain.

Problem 74QP If aluminum siding is fastened to a house with common iron nails, the siding may fall down due to corrosion. Considering the relative activity of aluminum and iron (see Figure 14.22), which metal will corrode? Would corrosion occur if aluminum nails were used? What about nickel nails? Reference Figure 14.22:

Problem 75QP If the chrome plating on an automobile bumper is damaged, will chromium or iron corrode first? Why?

Problem 76QP The zinc coating of galvanized iron protects the iron from corrosion. If the zinc coating is scratched to expose some iron, will the iron begin to corrode? Why?

Problem 77QP Indicate the oxidation number of nitrogen in each of the following compounds.

Problem 78QP The following table gives the results of reactions between five metals and solutions of their nitrate salts. NR means “no reaction” and MD means “metal displaced from solution.” From these results, arrange the five metals in order of decreasing chemical activity.

Problem 80QP Aqua regia is a mixture of concentrated HNO3 and concentrated HCl. It is often used for cleaning laboratory glassware, and it also dissolves platinum. Balance the equation for the dissolution of platinum metal:

Problem 79QP Balance the following equations, assuming the reactions occur in basic solution. Also, identify the oxidizing agent, the reducing agent, the element oxidized, and the element reduced in each reaction.

Problem 81QP Balance the following equation, assuming the reaction occurs in acidic solution: Also, identify the oxidizing agent, the reducing agent, the element oxidized, and the element reduced.

Problem 82QP The reaction that occurs in gas grills involves the burning of propane: Assign oxidation numbers to all of the reactants and identify the oxidizing and reducing agents.

Problem 84QP Why is gold a good metal to use in jewelry?

Problem 83QP In each of the following pairs, identify the strongest reducing agent. (a) Al and Pb (b) Zn and Ag (c) Cu and Mn (d) Cd and Mg

Problem 86QP A voltaic cell is created by using a copper cathode and a magnesium anode. The cathode is immersed in a solution of Cu2+ ions, and the anode is immersed in a solution of Mg2+ ions. A salt bridge of Na2SO4 is also used. What happens to the ions in the salt bridge as the reaction proceeds?

Problem 87QP Algae in swimming pools is sometimes treated by adding CuSO4 as a fungicide. Copper sulfate can be prepared by the addition of hot H2SO4 to Cu metal. Balance this equation, adding H+(aq) and H2O(l) as necessary.

Problem 85QP Why does brass cause your skin to turn green?

Problem 88QP Explain why bromide ion, Br–, can be oxidized but not reduced. Also, explain why the manganese in permanganate ion, can be reduced but not oxidized.

Problem 89QP Identify the oxidizing and reducing agents, and the oxidation and reduction half-reactions in each of the following chemical reactions.