Chapter 11, Problem 91A

Lead(ll) oxide is obtained by roasting galena, lead(ll) sulfide, in air. The unbalanced equation is:

$\text{PbS}\left(\text{s}\right){\text{+O}}_{\text{2}}\left(\text{g}\right)\to \text{PbO}\left(\text{s}\right){\text{+SO}}_{\text{2}}\left(\text{g}\right)$ )
a. Balance the equation, and determine the theoretical yield of $\text{PbO}$ if 200.0 g of PbS is heated.
b. What is the percent yield if 170.0 g of $\text{PbO}$ is obtained?

Interpretation Introduction

Interpretation : The balanced equation of chemical reaction is to be written and theoretical yield needs to be calculated.

Concept introduction : Lead oxide is obtained by roasting galena. Galena is an ore of Lead.

Roasting: It is a process to heat ore (sulphite, carbonate, sulphide) in presence of oxygen to convert it into oxide of metal.

Answer to Problem 91A

Theoretical yield is 187.47 g of PbO

Explanation of Solution

Step 1: Write balance chemical equation:

$\begin{array}{l}2PbS(s)+3O2(g)\to 2PbO(s)+2SO2(g)\\ 200g?\end{array}$

Step 2: convert mass of reactant to moles

$\begin{array}{c}MolarmassofPbS=239.26g/mole\\ Moles=\frac{Mass}{Molarmass}\\ MolesofPbS=\frac{200}{239.26}=0.84moles\end{array}$

Step 3: Convert moles of reactant to moles of product using mole ratio

2 moles of PbS produce = 2 moles of PbO

1 moles of PbS produce = 1 moles of PbO

0.84 moles of PbS produce = 0.84 moles of PbO

Step 4: Convert moles of product to mass (theoretical yield)

$\begin{array}{c}Molar\text{}massofPbO=223.19g/mole\\ Mass=Molarmass\times Moles\\ MassofPbO(Theoreticalyield)=223.19\times 0.84=187.47g\end{array}$

Interpretation Introduction

Interpretation:

If 170g of PbO was produce, the percent yield needs to be determined.

Concept introduction:

The percent yield can be calculated as follows:

$PercentYield=\frac{Actualyield}{Theoreticalyield}\times 100$

Answer to Problem 91A

Percent yield = 90.68%

Explanation of Solution

Actual yield = 170 g (given)

$\begin{array}{c}PercentYield=\frac{Actualyield}{Theoreticalyield}\times 100\\ =\frac{170}{187.47}\times 100=90.68\%\end{array}$