Chapter 6, Problem 22Q

(a)

Interpretation Introduction

Interpretation:

In Dolomite lime, calcium is in form of metal or ion has to be given.

Explanation of Solution

Dolomite lime is composed of limestone.  Calcium carbonate and magnesium carbonate are present in limestone.  Calcium carbonate is classified as an ionic compound as it contains a metal cation and a polyatomic anion.  Calcium is present as ${\text{Ca}}^{\text{2+}}$ ions in calcium carbonate.  Hence, in Dolomite lime, calcium is present as ion and not as metal.

(b)

Interpretation Introduction

Interpretation:

$\text{pH}$ of soil is corrected by limestone and the chemical equation for it has to be written.

Explanation of Solution

Limestone contains calcium carbonate and magnesium carbonate.  This reacts with the hydrogen ions present in the soil to form calcium ions, magnesium ions and water.  This is used to correct the $\text{pH}$ of soil.  Chemical equation for it can be written as shown below,

  $\begin{array}{l}{\text{CaCO}}_{\text{3}}{}_{\text{(s)}}\text{+}{\text{MgCO}}_{\text{3(s)}}\text{+}4{\text{H}}^{\text{+}}{}_{(aq)}\stackrel{}{\to }{\text{Ca}}^{\text{2+}}{}_{(aq)}\text{+}{\text{Mg}}^{\text{2+}}{}_{(aq)}\\ \text{+}2{\text{CO}}_{\text{2}}{}_{(g)}\text{+}2{\text{H}}_{\text{2}}{\text{O}}_{\text{(l)}}\end{array}$

(c)

Interpretation Introduction

Interpretation:

$\text{pH}$ of soil will rise or fall when limestone is added to the soil has to be given.

Explanation of Solution

Limestone contains calcium carbonate and magnesium carbonate.  This reacts with the hydrogen ions present in the soil to form calcium ions, magnesium ions and water.  This is used to correct the $\text{pH}$ of soil.  Chemical equation for it can be written as shown below,

  $\begin{array}{l}{\text{CaCO}}_{\text{3}}{}_{\text{(s)}}\text{+}{\text{MgCO}}_{\text{3(s)}}\text{+}4{\text{H}}^{\text{+}}{}_{(aq)}\stackrel{}{\to }{\text{Ca}}^{\text{2+}}{}_{(aq)}\text{+}{\text{Mg}}^{\text{2+}}{}_{(aq)}\\ \text{+}2{\text{CO}}_{\text{2}}{}_{(g)}\text{+}2{\text{H}}_{\text{2}}{\text{O}}_{\text{(l)}}\end{array}$

From the above equation it is clear that the hydrogen ions are reacted with carbonate ion to form carbon dioxide and water.  As the concentration of the hydrogen ion is reduced, the $\text{pH}$ of the soil rises.

(d)

Interpretation Introduction

Interpretation:

Dolomite lime should not be given to plants such as rhododendrons, azaleas, and camellias has to be explained.

Explanation of Solution

Limestone contains calcium carbonate and magnesium carbonate.  Chemical equation for the reaction of calcium carbonate and magnesium carbonate on reaction with acid in soil can be given as,

  $\begin{array}{l}{\text{CaCO}}_{\text{3}}{}_{\text{(s)}}\text{+}{\text{MgCO}}_{\text{3(s)}}\text{+}4{\text{H}}^{\text{+}}{}_{(aq)}\stackrel{}{\to }{\text{Ca}}^{\text{2+}}{}_{(aq)}\text{+}{\text{Mg}}^{\text{2+}}{}_{(aq)}\\ \text{+}2{\text{CO}}_{\text{2}}{}_{(g)}\text{+}2{\text{H}}_{\text{2}}{\text{O}}_{\text{(l)}}\end{array}$

From the above equation it is clear that the hydrogen ions are reacted with carbonate ion to form carbon dioxide and water.  As the concentration of the hydrogen ion is reduced, the $\text{pH}$ of the soil rises.

Plants such as rhododendrons, azaleas, and camellias require acidic soil for development and growth.  Addition of dolomite lime to the soil will increase the $\text{pH}$ and hence the soil will not be suitable for these plants to grow because dolomite lime neutralizes the acid.