Chapter 11, Problem 139QP

(a)

Interpretation Introduction

Interpretation:

Whether $\text{1}\text{.5}\text{M KBr}$ is expected to have the lowest freezing point or not is to be discussed, and the effects of this solution on osmotic pressure, vapor pressure and boiling point are to be compared.

Explanation of Solution

A solution that gives the highest number of particles has the lowest freezing point. $\text{1}\text{.5}m\text{ KBr}$ dissociates in water in the following way:

$\text{KBr}\left(s\right)\to {\text{K}}^{+}\left(aq\right)+{\text{Br}}^{-}\left(aq\right)$

One formula unit of $\text{1}\text{.5}\text{M KBr}$ breaking into two ions is less than those of $\text{1}\text{.5}{\text{M Al(NO}}_{\text{3}}{\text{)}}_{\text{3}}$ . So, $\text{1}\text{.5}\text{M KBr}$ will have a higher freezing point than $\text{1}\text{.5}{\text{M Al(NO}}_{\text{3}}{\text{)}}_{\text{3}}$ .

(b)

Interpretation Introduction

Interpretation:

Whether $\text{1}\text{.5}{\text{M Al(NO}}_{\text{3}}{\text{)}}_{\text{3}}$ is expected to have the lowest freezing point or not is to be discussed, and the effects of this solution on osmotic pressure, vapor pressure and boiling point are to be compared.

Explanation of Solution

$\text{1}\text{.5}{\text{M Al(NO}}_{\text{3}}{\text{)}}_{\text{3}}$ dissociates in water in the following way:

${\text{Al(NO}}_{\text{3}}{\text{)}}_{\text{3}}\left(s\right)\to {\text{Al}}^{3+}\left(aq\right)+3{\text{NO}}_3^{-}\left(aq\right)$

One formula unit of $\text{1}\text{.5}{\text{M Al(NO}}_{\text{3}}{\text{)}}_{\text{3}}$ breaks into four ions, which is the least among all the given solutions. So, $\text{1}\text{.5}{\text{M Al(NO}}_{\text{3}}{\text{)}}_{\text{3}}$ will have the lowest freezing point.

(c)

Interpretation Introduction

Interpretation:

Whether $\text{1}\text{.5}{\text{M Na}}_{\text{2}}{\text{CO}}_{\text{3}}$ is expected to have the lowest freezing point or not is to be discussed, and the effects of this solution on osmotic pressure, vapor pressure and boiling point are to be compared.

Explanation of Solution

$\text{1}\text{.5}{\text{M Na}}_{\text{2}}{\text{CO}}_{\text{3}}$ dissociates in water by the following way:

${\text{Na}}_{\text{2}}{\text{CO}}_{\text{3}}\left(s\right)\to 2{\text{Na}}^{+}\left(aq\right)+{\text{CO}}_3^{-}\left(aq\right)$

One formula unit of $\text{1}\text{.5}{\text{M Na}}_{\text{2}}{\text{CO}}_{\text{3}}$ breaking into three ions is less than those of $\text{1}\text{.5}{\text{M Al(NO}}_{\text{3}}{\text{)}}_{\text{3}}$ . So, $\text{1}\text{.5}{\text{M Na}}_{\text{2}}{\text{CO}}_{\text{3}}$ will have a higher freezing point than $\text{1}\text{.5}{\text{M Al(NO}}_{\text{3}}{\text{)}}_{\text{3}}$ .

(d)

Interpretation Introduction

Interpretation:

Whether $\text{1}\text{.5}{\text{M CH}}_{\text{3}}\text{OH}$ is expected to have the lowest freezing point or not is to be discussed, and the effects of this solution on osmotic pressure, vapor pressure and boiling point are to be compared.

Explanation of Solution

The given $\text{1}\text{.5}{\text{M CH}}_{\text{3}}\text{OH}$ aqueous solution dissociates in water in the following way:

${\text{CH}}_{\text{3}}\text{OH}\left(l\right)\to {\text{CH}}_{\text{3}}\text{OH}\left(aq\right)$

One formula unit of $\text{1}\text{.5}{\text{M CH}}_{\text{3}}\text{OH}$ does not dissociate. So, $\text{1}\text{.5}{\text{M CH}}_{\text{3}}\text{OH}$ will have a higher freezing point than that of $\text{1}\text{.5}{\text{M Al(NO}}_{\text{3}}{\text{)}}_{\text{3}}$ .

(e)

Interpretation Introduction

Interpretation:

Whether $\text{1}\text{.5}{\text{M MgCl}}_{\text{2}}$ is expected to have a lowest freezing point or not is to be discussed, and the effects of this solution on osmotic pressure, vapor pressure and boiling point are to be compared.

Explanation of Solution

$\text{1}\text{.5}{\text{M MgCl}}_{\text{2}}$ dissociates in water in the following way:

${\text{MgCl}}_{\text{2}}\left(s\right)\to {\text{Mg}}^{2+}\left(aq\right)+2{\text{Cl}}^{-}\left(aq\right)$

One formula unit of $\text{1}\text{.5}{\text{M MgCl}}_{\text{2}}$ breaking into three ions is less than those of $\text{1}\text{.5}{\text{M Al(NO}}_{\text{3}}{\text{)}}_{\text{3}}$ . So, $\text{1}\text{.5}{\text{M MgCl}}_{\text{2}}$ will have a higher freezing point than $\text{1}\text{.5}{\text{M Al(NO}}_{\text{3}}{\text{)}}_{\text{3}}$ .

As compared to pure water, each solution causes an increase in boiling point and osmotic pressure and a decrease in freezing point and vapor pressure. The order of the increasing effects on these properties is as follows:

$\text{d}<\text{a}<\text{c}=\text{e}<\text{b}$