Chapter 11, Problem 131QP

(A)

Interpretation Introduction

Interpretation:

Whether the response, “The solution is $0.20M$ in the molecules of ${\text{Mg(NO}}_{\text{3}}{\text{)}}_{\text{2}}$ � is correct or not for the given statement is to be identified.

Explanation of Solution

Consider the given statement, “The dissolution process of ${\text{Mg(NO}}_{\text{3}}{\text{)}}_{\text{2}}$ in water forms $0.20M$ solution�.

${\text{Mg(NO}}_{\text{3}}{\text{)}}_{\text{2}}$ is an example of a strong ionic electrolyte. It is completely dissociated when added to water. The dissolution process of ${\text{Mg(NO}}_{\text{3}}{\text{)}}_{\text{2}}$ in water can be expressed by the following equation:

${\text{Mg(NO}}_{\text{3}}{\text{)}}_{\text{2}}\left(s\right)+{\text{H}}_2\text{O}(l)\to {\text{Mg}}^{2+}\left(aq\right)+2{\text{NO}}_3{}^{-}\left(aq\right)$ ……(1)

The given response is incorrect because in water, ${\text{Mg(NO}}_{\text{3}}{\text{)}}_{\text{2}}$ dissociates completely to form ${\text{Mg}}^{2+}$ and ${\text{NO}}_3^{-}$ ions. So, no individual molecule of ${\text{Mg(NO}}_{\text{3}}{\text{)}}_{\text{2}}$ is present in the water solution.

(B)

Interpretation Introduction

Interpretation:

Whether the response, “ The solution is $0.20M$ in both ${\text{Mg}}^{2+}$ and ${{\text{(NO}}_3\text{)}}_2^{2-}$ ions� is correct or not for the given statement is to be identified.

Explanation of Solution

The given statement, “The dissolution process of ${\text{Mg(NO}}_{\text{3}}{\text{)}}_{\text{2}}$ in water forms $0.20M$ solution�.

In water, ${\text{Mg(NO}}_{\text{3}}{\text{)}}_{\text{2}}$ dissociates completely to form ${\text{Mg}}^{2+}$ and ${\text{NO}}_3^{-}$ ions. The individual concentration of the ions formed by dissolution depends on the mole ratio of the ions from the balanced equation (1). The mole ratio of ${\text{Mg}}^{2+}$ and ${\text{NO}}_3^{-}$ ions is $1:2$ . Thus, if ${\text{1 mole of Mg(NO}}_{\text{3}}{\text{)}}_{\text{2}}$ is added to water, it forms ${\text{1 mole of Mg}}^{2+}$ ions and ${\text{2 moles of NO}}_3^{-}$ ions.

Therefore, the given response is an incorrect response.

(C)

Interpretation Introduction

Interpretation:

Whether the response “ The solution is $0.20M$ in ${\text{Mg}}^{2+}$ and $0.40M$ in ${\text{NO}}_3^{-}$ ions� is correct or not for the given statement is to be identified.

Explanation of Solution

The given statement, “The dissolution process of ${\text{Mg(NO}}_{\text{3}}{\text{)}}_{\text{2}}$ in water forms $0.20M$ solution�.

The mole ratio of ${\text{Mg}}^{2+}$ and ${\text{NO}}_3^{-}$ ions formed in water from equation (1) is $1:2$ . The given concentration of ${\text{Mg(NO}}_{\text{3}}{\text{)}}_{\text{2}}$ solution in water is $0.20M$ .

So, the concentration of ${\text{Mg}}^{2+}$ ion is:

$1\times 0.20M=0.20M$ .

The concentration of ${\text{NO}}_3^{-}$ ions is:

$2\times 0.20M=0.40M$ .

Hence, the given response is correct as it best describes the dissolution process of ${\text{Mg(NO}}_{\text{3}}{\text{)}}_{\text{2}}$ in water to form $0.20M$ solution.

(D)

Interpretation Introduction

Interpretation:

Whether the given response, “The solution is $0.40M$ in total ions present� is correct or not for the given statement is to be identified.

Explanation of Solution

The given statement, “The dissolution process of ${\text{Mg(NO}}_{\text{3}}{\text{)}}_{\text{2}}$ in water to form $0.20M$ solution�.

The total concentration of the ions present in the aqueous solution is calculated by adding the concentration of both magnesium and nitrate ions.

$0.20M{\text{ Mg}}^{2+}+0.40M{\text{ NO}}_3^{-}=0.60M$

Since the total concentration of ions in the solution is $0.60M$ , the given response is an incorrect response.

(E)

Interpretation Introduction

Interpretation:

Whether the given response, “ ${\text{Mg(NO}}_{\text{3}}{\text{)}}_{\text{2}}$ is insoluble in water, thus no formation of ions takes place� is correct or not for the given statement is to be identified.

Explanation of Solution

Consider the given statement, “The dissolution process of ${\text{Mg(NO}}_{\text{3}}{\text{)}}_{\text{2}}$ in water forms $0.20M$ solution�.

${\text{Mg(NO}}_{\text{3}}{\text{)}}_{\text{2}}$ is a strong electrolyte and it completely dissociates in water to form ${\text{Mg}}^{2+}$ and ${\text{NO}}_3^{-}$ ions.

Therefore, the given response is an incorrect response.