Chapter U6.2, Problem 7E

(a)

Interpretation Introduction

Interpretation :

A balanced equation must be written for the extraction of elemental lead from PbO(s).

Concept Introduction :

A balanced chemical equation is the representation of a chemical reaction keeping number of each atom same in both the sides.

Answer to Problem 7E

  $\text{2PbO(s)}\to {\text{2Pb(s)+O}}_{\text{2}}\text{(g)}\text{.}$

Explanation of Solution

As per the balanced chemical equation 2 moles of elemental lead is produced along with 1 mole of oxygen from 2 moles of lead oxide. Number of Pb and O atoms are 2 in both the sides of the balanced chemical equation.

b)

Interpretation Introduction

Interpretation :

The process in order to convert all the lead oxide to elemental lead must be explained.

Concept Introduction :

Metal extraction from a metal oxide can be done in different processes. One of the commonly used processes is carbon reduction.

Answer to Problem 7E

Carbon reduction can be done with PbO(s) to convert it completely to elemental lead.

Explanation of Solution

  $\begin{array}{l}\text{PbO(s)+C(s)}\to \text{Pb(s)+CO(g)}\text{.}\\ \text{PbO(s)+CO(g)}\to {\text{Pb(s)+CO}}_{\text{2}}\text{(g)}\text{.}\end{array}$

From the reactions it is clear that if PbO(s) is not converted completely to elemental lead then the CO can also reduce the residual PbO(s) to elemental Pb(s).

c)

Interpretation Introduction

Interpretation :

The method to reverse the reaction must be explained.

Concept Introduction :

According to Le Chatelier’s principle, a reaction can be reversed by adjusting the temperature, pressure, concentration of reactants and products.

Answer to Problem 7E

More CO and CO₂ gas can be added to reverse the reaction. Pressure can be increased to reverse the first reaction.

Explanation of Solution

As the first reduction process produces CO, so addition of product (CO) can reverse the reaction. If pressure is increased then less mole side of a reaction is preferred. Thus increase in pressure also results in the reversal of the reaction.

d)

Interpretation Introduction

Interpretation :

The reason for Pb(s) which is kept in a jar with air for long time to not look shiny must be explained.

Concept Introduction :

Metal surface is shiny. This shiny appearance might be lost if it reacts with oxygen.

Answer to Problem 7E

Pb(s) kept in a jar with air for long time no longer looks shiny as lead is converted to lead oxide after reacting with oxygen present in the air.

Explanation of Solution

  $\text{Pb(s)+}\frac{\text{1}}{\text{2}}{\text{O}}_{\text{2}}\text{(g)=PbO(s)}\text{.}$

Thus lead metal is coated with a layer of oxide. So it is no longer looks shiny.