   Chapter 19, Problem 4PS

Chapter
Section
Textbook Problem

Balance the following redox equations. All occur in acid solution. (a) Sn(s) + H+(aq) → Sn2+(aq) + H2(g) (b) Cr2O72− (aq) + Fe2+(aq) → Cr3+(aq) + Fe3+(aq) (c) MnO2(s) + Cl−(aq) → Mn2+(aq) + Cl2(g) (d) CH2O(aq) + Ag+(aq) → HCO2H(aq) + Ag(s)

a)

Interpretation Introduction

Interpretation:

The redox equation in acidic solution has to be balanced.

a) Sn(s) + H+(aq) Sn2+(aq) + H2(g)

Concept introduction:

Steps for balancing redox reactions in ACIDIC solution:

1. 1. Recognize the reaction as an oxidation and reduction reaction.
2. 2. Separate two half reactions..
3. 3.  Balance half reactions by mass

Balance all atoms except H and O in half reaction.

Balance O atoms by adding water to the side missing O atoms.

Balance the H atoms by adding H+ to the side missing H atoms.

4. 4. Balance the charge by adding electrons to side with more total positive charge.
5. 5. Make the number of electrons the same in both half  reactions by multiplication, while avoiding fractional number of electrons.
6. 6.  Add the half reaction together and than simplyfy by cancelling out species that show up on both sides.
7. 7. Confirm that the reaction is balanced in number of atoms and charge on the both sides of the arrow.
Explanation

Given reaction:

Sn(s) + H+(aq)  Sn2+(aq) + H2(g)

Steps for balancing redox reactions in ACIDIC solution:

1. 1. Recognize the reaction as an oxidation and reduction reaction.

From the given reaction Sn increases their oxidation state 0 to +2. Therefore, it is an oxidation reaction.

2. 2. Separate two half reactions.

oxidation:      Sn(s)   Sn2+(aq)Reduction:     H+(aq) H2(g)

3. 3.  Balance half reactions by mass

Balance all atoms except H and O in half reaction.

oxidation:      Sn(s)   Sn2+(aq)Reduction:     H+(aq) H2(g)

Balance O atoms by adding water to the side missing O atoms.

oxidation:      Sn(s)   Sn2+(aq)Reduction:     H+(aq) H2(g)

Balance the H atoms by adding H+ to the side missing H atoms.

oxidation:      Sn(s)   Sn2+(aq)Reduction:     2H+(aq) H2(g)

4. 4. Balance the charge by adding electrons to side with more total positive charge.

oxidation:      Sn(s)   Sn2+(aq)+2eReduction:     2H+(aq)+2e H2(g)

5. 5

b)

Interpretation Introduction

Interpretation:

The redox equation in acidic solution has to be balanced.

b) Cr2O72-(aq) + Fe2+(aq) Cr3+(aq) + Fe3+(aq)

Concept introduction:

Steps for balancing redox reactions in ACIDIC solution:

1. 1. Recognize the reaction as an oxidation and reduction reaction.
2. 2. Separate two half reactions..
3. 3.  Balance half reactions by mass

Balance all atoms except H and O in half reaction.

Balance O atoms by adding water to the side missing O atoms.

Balance the H atoms by adding H+ to the side missing H atoms.

4. 4. Balance the charge by adding electrons to side with more total positive charge.
5. 5. Make the number of electrons the same in both half  reactions by multiplication, while avoiding fractional number of electrons.
6. 6.  Add the half reaction together and than simplyfy by cancelling out species that show up on both sides.
7. 7. Confirm that the reaction is balanced in number of atoms and charge on the both sides of the arrow.

c)

Interpretation Introduction

Interpretation:

The redox equation in acidic solution has to be balanced.

c) MnO2(aq) + Cl-(aq) Mn2+(aq) + Cl2(g)

Concept introduction:

Steps for balancing redox reactions in ACIDIC solution:

1. 1. Recognize the reaction as an oxidation and reduction reaction.
2. 2. Separate two half reactions..
3. 3.  Balance half reactions by mass

Balance all atoms except H and O in half reaction.

Balance O atoms by adding water to the side missing O atoms.

Balance the H atoms by adding H+ to the side missing H atoms.

4. 4. Balance the charge by adding electrons to side with more total positive charge.
5. 5. Make the number of electrons the same in both half  reactions by multiplication, while avoiding fractional number of electrons.
6. 6.  Add the half reaction together and than simplyfy by cancelling out species that show up on both sides.
7. 7. Confirm that the reaction is balanced in number of atoms and charge on the both sides of the arrow.

d)

Interpretation Introduction

Interpretation:

The redox equation in acidic solution has to be balanced.

d) CH2O(aq) + Ag+(aq) HCO2H(aq) + Ag(s)

Concept introduction:

Steps for balancing redox reactions in ACIDIC solution:

1. 1. Recognize the reaction as an oxidation and reduction reaction.
2. 2. Separate two half reactions..
3. 3.  Balance half reactions by mass

Balance all atoms except H and O in half reaction.

Balance O atoms by adding water.

Balance the H atoms by adding H+ to the side missing H atoms.

4. 4. Balance the charge by adding electrons to side with more total positive charge.
5. 5. Make the number of electrons the same in both half  reactions by multiplication, while avoiding fractional number of electrons.
6. 6.  Add the half reaction together and than simplyfy by cancelling out species that show up on both sides.
7. 7. Confirm that the reaction is balanced in number of atoms and charge on the both sides of the arrow.

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