Chapter U6.7, Problem 5E

(a)

Interpretation Introduction

Interpretation: Color of alizarin yellow when dissolved in water needs to be explained.

Concept Introduction: The concepts of Le Chatelier principle is also known as the Equilibrium law, are used to illustrate the effect of such changes on a chemical equilibrium. According to him, equilibrium adjusts the forward and backward reactions to acquire the changes which alter the conditions of equilibrium.

Answer to Problem 5E

Color of indicator is red.

Explanation of Solution

When an indicator is dissolved in water it dissociates as given below

  $\text{HIn}\left(\text{aq}\right){\text{+H}}_{\text{2}}\text{O}\left(\text{l}\right)\to {\text{H}}_{\text{3}}{\text{O}}^{\text{+}}\left(\text{aq}\right){\text{+In}}^{-}\left(\text{aq}\right)$

The acid and its conjugate base have different colors. At low pH values concentration of ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$ is high and so the equilibrium shift towards left and color of the solution is same as $\text{HIn}$ . At high pH values, the concentration of ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$ is low. Thus equilibrium shift to the right and the solution has the color of ${\text{In}}^{-}$ . Therefore, from table color of ${\text{In}}^{-}$ is red.

(b)

Interpretation Introduction

Interpretation: Color of bromocresol green when dissolved in water needs to be explained.

Concept Introduction: The concepts of Le Chatelier principle is also known as the Equilibrium law, are used to illustrate the effect of such changes on a chemical equilibrium. According to him, equilibrium adjusts the forward and backward reactions to acquire the changes which alter the conditions of equilibrium.

Answer to Problem 5E

Color of bromocresol green indicator is blue.

Explanation of Solution

When an indicator is dissolved in water it dissociates as given below

  $\text{HIn}\left(\text{aq}\right){\text{+H}}_{\text{2}}\text{O}\left(\text{l}\right)\to {\text{H}}_{\text{3}}{\text{O}}^{\text{+}}\left(\text{aq}\right){\text{+In}}^{-}\left(\text{aq}\right)$

The acid and its conjugate base have different colors. At low pH values the concentration of ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$ is high and so the equilibrium position shift towards left and the color of the solution is same as $\text{HIn}$ . At high pH values, the concentration of ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$ is low. Thus equilibrium shift to the right and the solution has the color of ${\text{In}}^{-}$ . Therefore, from table color of ${\text{In}}^{-}$ is blue.

(c)

Interpretation Introduction

Interpretation: Color of methyl red when dissolved in water needs to be explained.

Concept Introduction: The concepts of Le Chatelier principle is also known as the Equilibrium law, are used to illustrate the effect of such changes on a chemical equilibrium. According to him, equilibrium adjusts the forward and backward reactions to acquire the changes which alter the conditions of equilibrium.

Answer to Problem 5E

Color of methyl red indicator is yellow.

Explanation of Solution

When an indicator is dissolved in water it dissociates as given below

  $\text{HIn}\left(\text{aq}\right){\text{+H}}_{\text{2}}\text{O}\left(\text{l}\right)\to {\text{H}}_{\text{3}}{\text{O}}^{\text{+}}\left(\text{aq}\right){\text{+In}}^{-}\left(\text{aq}\right)$

The acid and its conjugate base have different colors. At low pH values the concentration of ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$ is high and so the equilibrium position shift towards left and color of the solution is same as $\text{HIn}$ . At high pH values, the concentration of ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$ is low. Thus equilibrium shift to the right and the solution has the color of ${\text{In}}^{-}$ . Therefore, from the table color of ${\text{In}}^{-}$ is yellow.

(d)

Interpretation Introduction

Interpretation: Color of phenol red when dissolved in water needs to be explained.

Concept Introduction: The concepts of Le Chatelier principle is also known as the Equilibrium law, are used to illustrate the effect of such changes on a chemical equilibrium. According to him, equilibrium adjusts the forward and backward reactions to acquire the changes which alter the conditions of equilibrium.

Answer to Problem 5E

Color of phenol red indicator is red.

Explanation of Solution

When an indicator is dissolved in water it dissociates as given below

  $\text{HIn}\left(\text{aq}\right){\text{+H}}_{\text{2}}\text{O}\left(\text{l}\right)\to {\text{H}}_{\text{3}}{\text{O}}^{\text{+}}\left(\text{aq}\right){\text{+In}}^{-}\left(\text{aq}\right)$

The acid and its conjugate base have different colors. At low pH values the concentration of ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$ is high and so the equilibrium shift towards the left and color of the solution is same as $\text{HIn}$ . At high pH values, the concentration of ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$ is low. Thus equilibrium shift to the right and the solution has the color of ${\text{In}}^{-}$ . Therefore, from table color of ${\text{In}}^{-}$ is red.