Chapter 4, Problem 1KSP

Interpretation Introduction

Interpretation:

The balanced net ionic equation is to be determined for the precipitation of FeSO₄ when aqueous solutions of $K_{2}S{O}_4$ and $FeC{l}_2$ are combined.

Concept introduction:

The ionic and net ionic equations can be written using the following steps:

Write the balanced molecular equation along with the state of each substance.

Rewrite the equation as a complete ionic equation, showing which compounds are dissociated into ions using the knowledge of solubility rules.

The compounds containing alkali metal cation or ammonium ion are watersoluble.

The compounds containing nitrate ion, chlorate ion, perchlorate ion, or acetate ion are watersoluble.

The compounds containing chloride ion, bromide ion, or iodide ion are watersoluble with the exception of compounds containing ${\text{Ag}}^{\text{+}}$, ${\text{Hg}}_2^{2+}$, or ${\text{Pb}}^{\text{2+}}$ ions.

The compounds containing sulfate ion are soluble with the exception of compounds containing ${\text{Ag}}^{\text{+}}$, ${\text{Hg}}_2^{2+}$, ${\text{Pb}}^{\text{2+}}$, ${\text{Ca}}^{\text{2+}}$, ${\text{Sr}}^{\text{2+}}$, or ${\text{Ba}}^{2+}$ ions.

The compounds containing carbonate ion, phosphate ion, and sulfide ion, and most metal hydroxides are insoluble in water except the compounds containing alkali metal cation or ammonium ion.

Spectator ions are the ions that exist as a reactant and a product in a chemical reaction.

Cancel out the spectator ions on both sides of the equation to get the net ionic equation.

Answer to Problem 1KSP

Correct answer: Option (b) is correct.

Explanation of Solution

Reason for correct option:

When aqueous solutions of K₂SO₄ and FeCl₂ are combined, the following reaction takes place:

${\text{K}}_{\text{2}}{\text{SO}}_{\text{4}}\left(aq\right)+{\text{FeCl}}_{\text{2}}\left(aq\right)\to {\text{FeSO}}_{\text{4}}\left(s\right)+2\text{KCl}\left(aq\right)$

The ionic equation for this reaction is:

${\text{2K}}^{+}\left(aq\right){\text{+ SO}}_4^{2-}\left(aq\right)+{\text{Fe}}^{2+}\left(aq\right){\text{+ 2Cl}}^{-}\left(aq\right)\to {\text{FeSO}}_{\text{4}}\left(s\right)+2{\text{K}}^{+}\left(aq\right){\text{+ 2Cl}}^{-}\left(aq\right)$

Cancel the spectator ions, ${\text{K}}^{\text{+}}{\text{and Cl}}^{-}$ on both sides to get the net ionic equation.

$\begin{array}{l}\underset{\_}{\cancel{{\text{2K}}^{+}\left(aq\right)}{\text{+ SO}}_4^{2-}\left(aq\right)+{\text{Fe}}^{2+}\left(aq\right)\text{+ }\cancel{{\text{2Cl}}^{-}\left(aq\right)}\to {\text{FeSO}}_{\text{4}}\left(s\right)+\cancel{2{\text{K}}^{+}\left(aq\right)}\text{+ }\cancel{{\text{2Cl}}^{-}\left(aq\right)}}\\ \underset{\_}{{\text{Fe}}^{2+}\left(aq\right)+{\text{ SO}}_4^{2-}\left(aq\right)\to {\text{FeSO}}_{\text{4}}\left(s\right)}\end{array}$

The compounds containing sulfate ion are soluble with the exception of compounds containing ${\text{Ag}}^{\text{+}}$, ${\text{Hg}}_2^{2+}$, ${\text{Pb}}^{\text{2+}}$, ${\text{Ca}}^{\text{2+}}$, ${\text{Sr}}^{\text{2+}}$, or ${\text{Ba}}^{2+}$ ions. Potassium and chloride are spectator ions. They exist as reactant and product.

Hence, option (b) is the correct answer.

Reasons for incorrect options:

Option (a) is incorrect because the given equation is the total ionic equation showing all the dissociated ions along with the spectator ions. The net ionic equation does not contain spectator ions.

Option (c) is incorrect because it is the molecular equation for the reaction.

Option (d) is incorrect as it is not a balanced net ionic equation.

Option (e) is incorrect as the equation contains spectator ions.

Hence, options (a), (c),(d), and (e) are incorrect.