Chemistry: An Atoms First Approach
Chemistry: An Atoms First Approach
2nd Edition
ISBN: 9781305079243
Author: Steven S. Zumdahl, Susan A. Zumdahl
Publisher: Cengage Learning
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Chapter 17, Problem 1RQ

What is a half-reaction? Why must the number of electrons lost in the oxidation half-reaction equal the number of electrons gained in the reduction half-reaction? Summarize briefly the steps in the half-reaction method for balancing redox reactions. What two items must be balanced in a redox reaction (or any reaction)?

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Interpretation Introduction

Interpretation:

The definition for half reaction and balancing of a redox reaction using half-reaction method is to be stated.

Concept introduction:

A redox reaction consists of two parts, one is oxidation and the other is reduction. These two reactions are called half reactions and they are involved in the change of oxidation number of the atoms present in the reaction.

To determine: The definition for half reaction and the steps involved in the balancing of a redox reaction using the half-reaction method; the reason behind the loss and gain of equal number of electrons in the oxidation and reduction half-reaction respectively; the steps involved in the half-reaction method for balancing the redox reaction and the two items that must be balanced in a redox reaction (or any chemical reaction).

Answer to Problem 1RQ

A half reaction is that type of reaction that involves either oxidation or reduction of a redox reaction.

It occurs because of the change in the oxidation number of the atoms involved in the reaction.

The number of electrons lost in the oxidation half-reaction must be equal to the number of electrons gained in the reduction half-reaction, to balance the charge of the overall reaction.

The number of electrons and atoms must be balanced in a redox reaction (or any reaction).

Explanation of Solution

The half reaction consists of either oxidation half or reduction half of a redox reaction.

The reaction in which transfer of electrons occur from one species to another is called redox reaction. The species which lose electron is said to be oxidized while the species which gain electron is reduced.

So, a redox reaction consists of two reactions, one is the oxidation half and the other is reduction half.

A half reaction can be either oxidation one or reduction one and it occurs because of the change on the oxidation number (state) of the species involved in the reaction.

The number of electrons lost during oxidation and those gained during reduction must be equal to maintain the overall charge of the redox reaction.

The equal gain and loss of electrons can be explained as follows,

Cu(s)Cu2+(aq)+2e- (1)

2Ag+(aq)+2e-2Ag(s) (2)

Adding the above two equations

Cu(s)+2Ag+(aq)Cu2+(aq)+2Ag(s) (3)

To balance the overall charge and mass, the equation (2) is multiplied by 2 that gives the final equation (3) that satisfies both the required conditions.

The steps involved in the balancing of redox reaction by half-reaction method can be summarized as follows.

In acidic medium, the reaction of reaction of Fe(II) with potassium permanganate is,

FeSO4+KMnO4+5H2SO4Fe2(SO4)3+MnSO4+H2O+K2SO4 (4)

The ionic reaction can be represented as,

Fe2++MnO4-+H+Fe3++Mn2++H2O (5)

  • The oxidation half and reduction half of the reaction, respectively, is,

Fe2+Fe3+ (6)

MnO4-Mn2+ (7)

  • Balance the oxidation half-reaction by the addition of one electron to the right hand side of the reaction.

Fe2+Fe3++e- (8)

  • Balance the reduction half-reaction. As the oxygen atoms are not balanced, try to balance them by adding equal number of water molecules on the opposite side.

MnO4-Mn2++4H2O (9)

  • Balance the hydrogen atoms by adding equal number of H+ on the opposite side.

MnO4+8H+Mn2++4H2O (10)

  • The charge on Mn at left side is +7 while on right side is +5 Balance the charge on both sides by adding 5 electrons on the left hand side.

MnO4-+8H++5e-Mn2++4H2O (11)

  • To balance the overall charge, multiply equation (8) by 5.

5Fe2+5Fe3++5e- (12)

  • Add equation (11) and (12).

MnO4-+8H++5Fe2++5e-Mn2++4H2O+5Fe3++5e- (13)

  • To write the final equation, cancel out the electrons on both the sides.

MnO4-+8H++5Fe2+Mn2++4H2O+5Fe3+ (14)

The number of atoms and electrons must be balanced in a redox reaction (or any chemical reaction).

According to the law of conservation of mass, mass can neither be created nor destroyed in a chemical reaction. Therefore mass of every species must be conserved in the reaction. Therefore to balance mass, the number of atoms must be balanced in a chemical equation. Besides this the charge on both the sides of the reaction must be balanced to maintain the overall charge of the reaction.

Conclusion

The redox reaction consists of the reduction half-reaction and oxidation half-reaction. The reaction must be properly balanced to maintain the law of conservation of mass and overall charge.

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Chapter 17 Solutions

Chemistry: An Atoms First Approach

Ch. 17 - Prob. 2ALQCh. 17 - Prob. 3ALQCh. 17 - Prob. 4ALQCh. 17 - Sketch a cell that forms iron metal from iron(II)...Ch. 17 - Which of the following is the best reducing agent:...Ch. 17 - Prob. 7ALQCh. 17 - Prob. 8ALQCh. 17 - Explain why cell potentials are not multiplied by...Ch. 17 - What is the difference between and ? When is equal...Ch. 17 - Prob. 11ALQCh. 17 - Look up the reduction potential for Fe3+ to Fe2+....Ch. 17 - Prob. 13ALQCh. 17 - Is the following statement true or false?...Ch. 17 - Prob. 15RORRCh. 17 - Assign oxidation numbers to all the atoms in each...Ch. 17 - Specify which of the following equations represent...Ch. 17 - The Ostwald process for the commercial production...Ch. 17 - Prob. 19QCh. 17 - Prob. 20QCh. 17 - When magnesium metal is added to a beaker of...Ch. 17 - How can one construct a galvanic cell from two...Ch. 17 - The free energy change for a reaction, G, is an...Ch. 17 - What is wrong with the following statement: The...Ch. 17 - When jump-starting a car with a dead battery, the...Ch. 17 - Prob. 26QCh. 17 - Prob. 27QCh. 17 - Consider the following electrochemical cell: a. If...Ch. 17 - Balance the following oxidationreduction reactions...Ch. 17 - Prob. 30ECh. 17 - Prob. 31ECh. 17 - Prob. 32ECh. 17 - Chlorine gas was first prepared in 1774 by C. W....Ch. 17 - Gold metal will not dissolve in either...Ch. 17 - Prob. 35ECh. 17 - Consider the following galvanic cell: a. Label the...Ch. 17 - Prob. 37ECh. 17 - Sketch the galvanic cells based on the following...Ch. 17 - Prob. 39ECh. 17 - Prob. 40ECh. 17 - Prob. 41ECh. 17 - Prob. 42ECh. 17 - Prob. 43ECh. 17 - Give the standard line notation for each cell in...Ch. 17 - Prob. 45ECh. 17 - Prob. 46ECh. 17 - Prob. 47ECh. 17 - Prob. 48ECh. 17 - Prob. 49ECh. 17 - The amount of manganese in steel is determined by...Ch. 17 - Prob. 51ECh. 17 - Prob. 52ECh. 17 - Estimate for the half-reaction 2H2O+2eH2+2OH given...Ch. 17 - Prob. 54ECh. 17 - Glucose is the major fuel for most living cells....Ch. 17 - Direct methanol fuel cells (DMFCs) have shown some...Ch. 17 - Prob. 57ECh. 17 - Using data from Table 17-1, place the following in...Ch. 17 - Answer the following questions using data from...Ch. 17 - Prob. 60ECh. 17 - Consider only the species (at standard conditions)...Ch. 17 - Prob. 62ECh. 17 - Prob. 63ECh. 17 - Prob. 64ECh. 17 - Prob. 65ECh. 17 - Prob. 66ECh. 17 - A galvanic cell is based on the following...Ch. 17 - Prob. 68ECh. 17 - Consider the concentration cell shown below....Ch. 17 - Prob. 70ECh. 17 - The overall reaction in the lead storage battery...Ch. 17 - Prob. 72ECh. 17 - Consider the cell described below:...Ch. 17 - Consider the cell described below:...Ch. 17 - Prob. 75ECh. 17 - Prob. 76ECh. 17 - Prob. 77ECh. 17 - Prob. 78ECh. 17 - Prob. 79ECh. 17 - An electrochemical cell consists of a nickel metal...Ch. 17 - An electrochemical cell consists of a standard...Ch. 17 - Prob. 82ECh. 17 - Consider a concentration cell that has both...Ch. 17 - Prob. 84ECh. 17 - Prob. 85ECh. 17 - Prob. 86ECh. 17 - Consider the following galvanic cell at 25C:...Ch. 17 - Prob. 88ECh. 17 - Prob. 89ECh. 17 - Prob. 90ECh. 17 - Prob. 91ECh. 17 - The solubility product for CuI(s) is 1.1 102...Ch. 17 - How long will it take to plate out each of the...Ch. 17 - The electrolysis of BiO+ produces pure bismuth....Ch. 17 - What mass of each of the following substances can...Ch. 17 - Prob. 96ECh. 17 - An unknown metal M is electrolyzed. It took 74.1 s...Ch. 17 - Electrolysis of an alkaline earth metal chloride...Ch. 17 - What volume of F2 gas, at 25C and 1.00 atm, is...Ch. 17 - What volumes of H2(g) and O2(g) at STP are...Ch. 17 - Prob. 101ECh. 17 - A factory wants to produce 1.00 103 kg barium...Ch. 17 - It took 2.30 min using a current of 2.00 A to...Ch. 17 - A solution containing Pt4+ is electrolyzed with a...Ch. 17 - A solution at 25C contains 1.0 M Cd2+, 1.0 M Ag+,...Ch. 17 - Consider the following half-reactions: A...Ch. 17 - In the electrolysis of an aqueous solution of...Ch. 17 - Copper can be plated onto a spoon by placing the...Ch. 17 - Prob. 109ECh. 17 - Prob. 110ECh. 17 - Prob. 111ECh. 17 - What reaction will take place at the Cathode and...Ch. 17 - Gold is produced electrochemically from an aqueous...Ch. 17 - Prob. 114AECh. 17 - The saturated calomel electrode. abbreviated SCE....Ch. 17 - Consider the following half-reactions: Explain why...Ch. 17 - Consider the standard galvanic cell based on the...Ch. 17 - Prob. 118AECh. 17 - The black silver sulfide discoloration of...Ch. 17 - Prob. 120AECh. 17 - When aluminum foil is placed in hydrochloric acid,...Ch. 17 - Prob. 122AECh. 17 - Prob. 123AECh. 17 - The overall reaction and equilibrium constant...Ch. 17 - What is the maximum work that can be obtained from...Ch. 17 - The overall reaction and standard cell potential...Ch. 17 - Prob. 127AECh. 17 - Prob. 128AECh. 17 - Prob. 129AECh. 17 - Prob. 130AECh. 17 - Prob. 131AECh. 17 - Prob. 132AECh. 17 - Prob. 133AECh. 17 - Prob. 134CWPCh. 17 - Consider a galvanic cell based on the following...Ch. 17 - Consider a galvanic cell based on the following...Ch. 17 - Consider a galvanic cell based on the following...Ch. 17 - An electrochemical cell consists of a silver metal...Ch. 17 - An aqueous solution of PdCl2 is electrolyzed for...Ch. 17 - Prob. 140CPCh. 17 - Prob. 141CPCh. 17 - The overall reaction in the lead storage battery...Ch. 17 - Consider the following galvanic cell: Calculate...Ch. 17 - Prob. 144CPCh. 17 - A galvanic cell is based on the following...Ch. 17 - Prob. 146CPCh. 17 - The measurement of pH using a glass electrode...Ch. 17 - Prob. 148CPCh. 17 - A galvanic cell is based on the following...Ch. 17 - Prob. 150CPCh. 17 - Prob. 151CPCh. 17 - Prob. 152CPCh. 17 - Consider the following galvanic cell: A 15 0-mole...Ch. 17 - When copper reacts with nitric acid, a mixture of...Ch. 17 - The following standard reduction potentials have...Ch. 17 - An electrochemical cell is set up using the...Ch. 17 - Three electrochemical cells were connected in...Ch. 17 - A silver concentration cell is set up at 25C as...Ch. 17 - A galvanic cell is based on the following...Ch. 17 - Prob. 160MP
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