   Chapter 18, Problem 140CP

Chapter
Section
Textbook Problem

# Balance the following equations by the half-reaction method.  a. Fe ( s )   +   HCl ( a q )   →   HFeCl 4 ( a q ) + H 2 ( g )   b. IO 3 − ( a q )   +   I − ( a q )   → Acid   I 3 − ( a q )   c. Cr ( NCS ) 6 4 − ( a q )   +   Ce 4 + ( a q ) → Acid   Cr 3 + ( a q )   +   Ce 3 + ( a q ) +   NO 3 − ( a q )   +   CO 2 ( g )   +   SO 4 2 − ( a q )   d. CrI 3 ( s )   +   Cl 2 ( g )   → Base   CeO 4 2 − ( a q )   +   IO 4 − ( a q )   +   Cl − ( a q )   e. Fe ( CN ) 6 4 − ( a q )   +   Ce 4 + ( a q )   → Base Ce ( OH ) 3 ( s )   +   Fe ( OH ) 3 ( s )   +   CO 3 2 − ( a q )   +   NO 3 − ( a q )

(a)

Interpretation Introduction

Interpretation:

The following equations are balanced by the half-reaction method

Concept introduction:

The chemical equation is said to be balanced when the number of atoms of chemical species on the reactant side is equal to the number of chemical species on the product side. In the half reaction method, each half reaction that is oxidation and reduction reaction is separately balanced.

To determine: The given balanced chemical reaction by the half-reaction method.

Explanation

Given

The given reaction is,

Fe(s)+HCl(aq)HFeCl4(aq)+H2(g) .

In this equation, the oxidation state of hydrogen decreased from +1 to 0 and the oxidation state of iron increased from 0 to +3 . So, hydrogen undergoes reduction and iron undergoes oxidation.

Also, in this equation there are spectator ions, H+,Clin HFeCl4 and Cl in HCl which are not directly involved in the redox reaction so they are eliminated and the equation becomes,

Fe(s)+H+(aq)Fe3+(aq)+H2(g)

The reduction half cell reaction is,

H+(aq)H2(g)

The oxidation half cell reaction is,

Fe(s)Fe3+(aq)

Now balance H atoms in the reduction half reaction by adding H+ ions.

H+(aq)+H+(aq)H2(g)

Finally, balance charge using electrons.

2H+(aq)+2eH2(g)

Now the charge in oxidation half reaction using electrons is to be balanced.

Fe(s)Fe3+(aq)+3e

The oxidation half reaction is multiplied by 2 and the reduction reaction by 3 to cancel electrons and add them

(b)

Interpretation Introduction

Interpretation:

The following equations are balanced by the half-reaction method

Concept introduction:

The chemical equation is said to be balanced when the number of atoms of chemical species on the reactant side is equal to the number of chemical species on the product side. In the half reaction method, each half reaction that is oxidation and reduction reaction is separately balanced.

(c)

Interpretation Introduction

Interpretation:

The following equations are balanced by the half-reaction method

Concept introduction:

The chemical equation is said to be balanced when the number of atoms of chemical species on the reactant side is equal to the number of chemical species on the product side. In the half reaction method, each half reaction that is oxidation and reduction reaction is separately balanced.

To determine: The given balanced chemical reaction by the half-reaction method.

(d)

Interpretation Introduction

Interpretation:

The following equations are balanced by the half-reaction method

Concept introduction:

The chemical equation is said to be balanced when the number of atoms of chemical species on the reactant side is equal to the number of chemical species on the product side. In the half reaction method, each half reaction that is oxidation and reduction reaction is separately balanced.

To determine: The given balanced chemical reaction by the half-reaction method.

(e)

Interpretation Introduction

Interpretation:

The following equations are balanced by the half-reaction method

Concept introduction:

The chemical equation is said to be balanced when the number of atoms of chemical species on the reactant side is equal to the number of chemical species on the product side. In the half reaction method, each half reaction that is oxidation and reduction reaction is separately balanced.

To determine: The given balanced chemical reaction by the half-reaction method.

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