Chapter 21, Problem 71PS

(a)

Interpretation Introduction

Interpretation:

The maximum amount of ${\text{SO}}_{\text{2}}$ that is allowed to be exhausted to the atmosphere is to be calculated.

Concept introduction:

The contact process is the method of producing sulfuric acid in the high concentrations needed for industrial process. The process involved combining of sulfur and oxygen to form sulfur dioxide as follows,

    $\text{S}\left(\text{s}\right)+{\text{O}}_{\text{2}}\left(\text{g}\right)\to {\text{SO}}_{\text{2}}\left(\text{g}\right)$

Adding an excess of oxygen to sulfur dioxide in the presence of catalyst, the sulfur trioxide is formed. The sulfur trioxide is added to sulfuric acid which gives rise to disulfuric acid (oleum). Oleum is reacted with water to form concentrated sulfuric acid. The reactions involved is written as follows:

    $\begin{array}{l}{\text{2SO}}_{\text{2}}\left(\text{g}\right)+{\text{O}}_{\text{2}}\left(\text{g}\right)\rightleftharpoons {\text{2SO}}_{\text{3}}\left(\text{g}\right)\\ {\text{SO}}_{\text{3}}\left(\text{g}\right)+{\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}\left(\text{l}\right)\to {\text{H}}_{\text{2}}{\text{S}}_{\text{2}}{\text{O}}_{\text{7}}\left(\text{l}\right)\\ {\text{H}}_{\text{2}}{\text{S}}_{\text{2}}{\text{O}}_{\text{7}}\left(\text{l}\right)+{\text{H}}_{\text{2}}\text{O}\left(\text{l}\right)\to 2{\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}\left(\text{l}\right)\end{array}$                                                             (1)

 $\begin{array}{l}\text{Number}\text{of}\text{moles}\text{=}\frac{\text{Mass}}{\text{Molecular}\text{mass}}\\ \text{Mass}\text{=}\text{Number}\text{of}\text{moles}\text{×}\text{Molecular}\text{mass}\end{array}$

(b)

Interpretation Introduction

Interpretation:

To calculate the mass of calcium hydroxide is needed to remove the sulfur dioxide.

Introduction:

In the contact process, for making sulfuric acid, if enough sulfur is burned to sulfur dioxide to produce anhydrous sulfuric acid. The sulfur dioxide is vented to the atmosphere. To prevent any ${\text{SO}}_{\text{2}}$ from reaching atmosphere is to exhaust the gas with slaked lime $\left(\text{Ca}{\left(\text{OH}\right)}_{\text{2}}\right)$:

    $\begin{array}{l}\text{Ca}{\left(\text{OH}\right)}_{\text{2}}\left(\text{s}\right)+{\text{SO}}_{\text{2}}\left(\text{g}\right)\to {\text{CaSO}}_{\text{3}}\left(\text{s}\right)+{\text{H}}_{\text{2}}\text{O}\left(\text{l}\right)\\ 2{\text{CaSO}}_{\text{3}}\left(\text{s}\right)+{\text{O}}_{\text{2}}\left(\text{g}\right)\to {\text{2CaSO}}_{\text{4}}\left(\text{s}\right)\end{array}$ (1)

$\begin{array}{l}\text{Number}\text{of}\text{moles}\text{=}\frac{\text{Mass}}{\text{Molecular}\text{mass}}\\ \text{Mass}\text{=}\text{Number}\text{of}\text{moles}\text{×}\text{Molecular}\text{mass}\end{array}$