Chapter 4, Problem 1RQ

The (aq) designation listed after a solute indicates the process of hydration. Using KBr(aq) and C₂H₅OH(aq) as your examples, explain the process of hydration for soluble ionic compounds and for soluble covalent compounds.

Interpretation Introduction

Interpretation: The process of hydration for soluble ionic compounds and soluble covalent compounds with $\text{KBr}$ and ${\text{C}}_{\text{2}}{\text{H}}_{\text{5}}\text{OH}$ as example to be explained.

Concept Introduction: When an ionic compound is dissolved in water, the positive ends of the water molecules are attracted to the negative charged ions and that negative ends are attracted to the positive charged ions. This process is called as hydration.

Answer to Problem 1RQ

Answer

Soluble ionic compounds have to tendency to breakup into their positive and negatively charged ions when they are dissolved into solution.

In $\text{KBr}$, the dissolution of the ionic compound takes place as,

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

In the hydration process for ions, the partial negative end of the polar water molecules surrounds and stabilizes the cations in the solution. The water molecules present here would align themselves in such a way that the oxygen end of water aligns with the ${\text{K}}^{\text{+}}$ ions. The anions in the solution are surrounded by the negative ions that are stabilized in water, having the partial positive end of the polar water.

In the case of ${\text{Br}}^{\text{-}}$ ions, the ${\text{Br}}^{\text{-}}$ ions are aligned by the hydrogen end of water.

This is assumption when an aqueous solution (aq) is placed after an ionic compound.

Soluble covalent compounds are that compound that doesn’t have to tendency to break into ions when they are dissolved in solution.

Consider, ${\text{C}}_{\text{2}}{\text{H}}_{\text{5}}\text{OH}$ as a polar covalent compound which has a partial negative end and partial positive end. It doesn’t have the tendency to breakup into ions when they are dissolved in water.

The hydration process for polar covalent solutes takes place when the covalent solutes and solvents align themselves such that their opposite charged parts attract each other.

The partial negative end of ${\text{C}}_{\text{2}}{\text{H}}_{\text{5}}\text{OH}$ is aligned by the hydrogen of water molecules and the partial positive end of ${\text{C}}_{\text{2}}{\text{H}}_{\text{5}}\text{OH}$ is aligned by the oxygens of the water molecules.

This is the hydration process for polar covalent compounds. This is assumption when an aqueous solution (aq) is placed after an ionic compound.

It is difficult to predict the partial negative ends and partial positive ends of polar covalent compounds.

Explanation of Solution

Explanation

To explain the process of hydration in soluble ionic compounds

The process of hydration can be defined as dissolution of ionic compound in water, where

the positive ends of the water molecules are attracted to the negative charged ions and that negative ends are attracted to the positive charged ions.

When an ionic compound that is soluble in water can break apart into their ions upon dissolution such ionic compounds are called as soluble ionic compounds.

Taking the example of $\text{KBr}$ as a soluble ionic compound,

The dissolution of $\text{KBr}$ in water will result in formation of ${\text{K}}^{\text{+}}\text{and}{\text{Br}}^{\text{-}}$ ions.

The equation can be given as,

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

In the hydration process for ions, the partial negative end of the polar water molecules surrounds and stabilizes the cations in the solution. The water molecules present here would align themselves in such a way that the oxygen end of water aligns with the ${\text{K}}^{\text{+}}$ ions. The anions in the solution are surrounded by the negative ions that are stabilized in water, having the partial positive end of the polar water.

In the case of ${\text{Br}}^{\text{-}}$ ions, the ${\text{Br}}^{\text{-}}$ ions are aligned by the hydrogen end of water.

This is assumption when an aqueous solution (aq) is placed after an ionic compound.

The separation of ions that are placed in solution is surrounded by the water that is permitable. There is an enthalpy change. The enthalpy change for this process is called as hydration enthalpy.

When a compound is made to get soluble in water, there is no break apart into their ions upon dissolution such ionic compounds are called as soluble covalent compounds.

To explain the process of hydration in soluble covalent compound

Soluble covalent compounds are that compound that doesn’t have to tendency to break into ions when they are dissolved in solution.

Consider, ${\text{C}}_{\text{2}}{\text{H}}_{\text{5}}\text{OH}$ as a polar covalent compound which has a partial negative end and partial positive end. It doesn’t have the tendency to breakup into ions when they are dissolved in water.

The hydration process for polar covalent solutes takes place when the covalent solutes and solvents align themselves such that their opposite charged parts attract each other.

The partial negative end of ${\text{C}}_{\text{2}}{\text{H}}_{\text{5}}\text{OH}$ is aligned by the hydrogen of water molecules and the partial positive end of ${\text{C}}_{\text{2}}{\text{H}}_{\text{5}}\text{OH}$ is aligned by the oxygens of the water molecules.

This is the hydration process for polar covalent compounds. This is assumption when an aqueous solution (aq) is placed after an ionic compound.

It is difficult to predict the partial negative ends and partial positive ends of polar covalent compounds.

Conclusion

The concept of hydration of soluble ionic and covalent compounds were explained with

$\text{KBr}$ and ${\text{C}}_{\text{2}}{\text{H}}_{\text{5}}\text{OH}$ as examples.