Chapter 23, Problem 23.31QP

Complete and balance the following equations. Note any catalyst used.

1. a ${\text{C}}_2{\text{H}}_4+{\text{O}}_2\stackrel{}{\to }$
2. b ${\text{CH}}_2\text{}=\text{}{\text{CH}}_2+{\text{MnO}}_4{}^{-}+{\text{H}}_2\text{O}\stackrel{}{\to }$
3. c ${\text{CH}}_2\text{}=\text{}{\text{CH}}_2+{\text{Br}}_2\stackrel{}{\to }$
4. d
5. e

Interpretation Introduction

Interpretation:

For the given reactions, the equation has to be completed and balanced.

Concept Introduction:

Combustion reaction is the one in which, the substance is burnt in presence of oxygen.  If any hydrocarbon is burnt in presence of oxygen, the products obtained is carbon dioxide and water only.

Answer to Problem 23.31QP

The balanced equation for the given reaction can be written as,

${\text{C}}_{\text{2}}{\text{H}}_{\text{4}}{\text{+ 3O}}_{\text{2}}\stackrel{}{\to }{\text{ 2CO}}_{\text{2}}{\text{+ 2H}}_{\text{2}}\text{O}$

Explanation of Solution

The given reaction in the problem statement is a combustion reaction and hence, the product obtained will be carbon dioxide and water only.  Hence, the raw equation can be written as,

${\text{C}}_{\text{2}}{\text{H}}_{\text{4}}{\text{+ O}}_{\text{2}}\stackrel{}{\to }{\text{ CO}}_{\text{2}}{\text{+ H}}_{\text{2}}\text{O}$

As the total number of atoms present in both reactants and products must be equal, balancing has to be done.  To balance the carbon atom in both sides, the product side has to be multiplied by 2.  This leads, balancing of both carbon and hydrogen atoms on both sides.

${\text{C}}_{\text{2}}{\text{H}}_{\text{4}}{\text{+ O}}_{\text{2}}\stackrel{}{\to }{\text{ 2CO}}_{\text{2}}{\text{+ 2H}}_{\text{2}}\text{O}$

Oxygen count was six in product side.  But in the reactant side it is two.  Hence, multiplying by three on reactant side balances the oxygen atom also on both sides.  Therefore, the balanced chemical equation for the given reaction can be given as,

${\text{C}}_{\text{2}}{\text{H}}_{\text{4}}{\text{+ 3O}}_{\text{2}}\stackrel{}{\to }{\text{ 2CO}}_{\text{2}}{\text{+ 2H}}_{\text{2}}\text{O}$

Conclusion

The given incomplete combustion reaction is completed and the balanced chemical equation also written.

Interpretation Introduction

Interpretation:

For the given reactions, the equation has to be completed and balanced.

Concept Introduction:

Oxidation is loss of electron by a species.  This also can be said as addition of oxygen.  Reduction is a process in which electrons are gained by a species.

Answer to Problem 23.31QP

The balanced equation for the given reaction can be written as,

Explanation of Solution

$\begin{array}{l}{\text{Reduction: MnO}}_{\text{4}}{}^{\text{-}}\stackrel{}{\to }{\text{ MnO}}_{\text{2}}\hfill \\ {\text{ Balance O: MnO}}_{\text{4}}{}^{\text{-}}{\text{+ 2H}}_{\text{2}}\text{O }\stackrel{}{\to }{\text{ MnO}}_{\text{2}}{\text{+ 4OH}}^{\text{-}}\hfill \\ {\text{ Balance e}}^{\text{-}}{\text{: MnO}}_{\text{4}}{}^{\text{-}}{\text{+ 2H}}_{\text{2}}{\text{O + 3e}}^{\text{-}}\stackrel{}{\to }{\text{ MnO}}_{\text{2}}{\text{+ 4OH}}^{\text{-}}\hfill \end{array}$

Add half-reactions:

Therefore, the complete equation for the given reaction can be given as,

Conclusion

The balanced equation for the given reaction was written.

Interpretation Introduction

Interpretation:

For the given reactions, the equation has to be completed and balanced.

Concept Introduction:

Bromination of alkene happens without any catalyst in carbon tetrachloride.  The bromine atom adds across the double bond reducing the double bond to a single bond.

Answer to Problem 23.31QP

The balanced equation for the given reaction can be written as,

Explanation of Solution

Bromination across the double bond.

Conclusion

The given bromination reaction was completed and the product was written with balanced equation.

Interpretation Introduction

Interpretation:

For the given reactions, the equation has to be completed and balanced.

Concept Introduction:

Bromination of aromatic compound happens in presence of catalyst.  Usually this does not occur in absence of catalyst.  The position of bromination in the aromatic ring depends upon the group already substituted in the ring.

Answer to Problem 23.31QP

The balanced equation for the given reaction can be written as,

Explanation of Solution

Bromination of toluene takes place in presence of catalyst with bromine.  As methyl is a para directing group, the bromine atom is substituted in the para position.  By considering this, the complete reaction can be given as,

Conclusion

The given bromination reaction was completed and the product was written with balanced equation.

Interpretation Introduction

Interpretation:

For the given reactions, the equation has to be completed and balanced.

Concept Introduction:

Nitration of aromatic compound happens when concentrated nitric acid and sulphuric acid is added to it.  The position of nitro group substitution depends upon the position of the already substituted group present in it.

Answer to Problem 23.31QP

The balanced equation for the given reaction can be written as,

Explanation of Solution

Nitration of toluene takes place in presence of nitric acid and sulphuric acid.  As methyl is a para directing group, the nitro group is substituted in the para position.  By considering this, the complete reaction can be given as,

Conclusion

The given reaction was completed and the product was written with balanced equation.