Chapter 4, Problem 4.146QP

Interpretation Introduction

Interpretation:

The molecular equation and net ionic equation of given reaction has to be written.  The amount of solution formed when mercury nitrate reacts with hydrogen sulfide has to be calculated.

Concept introduction:

A chemical equation is the figurative representation of chemical reaction.  In a chemical equation the reactants are in the left side and the products are in the right side.  A balanced chemical equation serves as an easy tool for understanding a chemical reaction.  There are mainly three types of chemical equations, molecular equations, complete ionic equation and net ionic equation.

In molecular equations the reactants and products are represented as molecular substances, even though they exist as ions in solution phase.  The molecular equation for the reaction between $\text{Ca}{\left(\text{OH}\right)}_{\text{2}}$ and ${\text{Na}}_{\text{2}}{\text{CO}}_{\text{3}}$ in solution phase is given below.

${\text{Ca(OH)}}_{\text{2(aq)}}{\text{+Na}}_{\text{2}}{\text{CO}}_{\text{3(aq)}}\stackrel{}{\to }{\text{CaCO}}_{\text{3(s)}}{\text{+2NaOH}}_{\text{(aq)}}$

This equation is helpful in understanding the reactants and products involved in the reaction.

In complete ionic equations the electrolytes are represented as its ions.  Soluble compounds exist as ions in solution.  Complete ionic equation is helpful in understanding the reaction at ionic level.  The complete ionic equation for the reaction between $\text{Ca}{\left(\text{OH}\right)}_{\text{2}}$ and ${\text{Na}}_{\text{2}}{\text{CO}}_{\text{3}}$ is given below.

${\text{Ca}}^{\text{2+}}{}_{\text{(aq)}}{\text{+2OH}}^{\text{-}}{}_{\text{(aq)}}{\text{+2Na}}^{\text{+}}{}_{\text{(aq)}}{\text{+CO}}_{\text{3}}{{}^{\text{2-}}}_{\text{(aq)}}\stackrel{}{\to }{\text{CaCO}}_{\text{3(s)}}{\text{+2Na}}^{\text{+}}{}_{\text{(aq)}}{\text{+2OH}}^{\text{-}}{}_{\text{(aq)}}$

The solid ${\text{CaCO}}_{\text{3}}$ is insoluble and it exist as solid in solution.

In net ionic equations the ions that are common in the reactant and product sides( Spectator ions) are cancelled.  These spectator ions are not participating in the chemical reactions.  The net ionic equation for the reaction between $\text{Ca}{\left(\text{OH}\right)}_{\text{2}}$ and ${\text{Na}}_{\text{2}}{\text{CO}}_{\text{3}}$ is given below.  As hydroxide ions and sodium ions are common in both the side it is neglected from the equation.

${\text{Ca}}^{\text{2+}}{}_{\text{(aq)}}\text{+}{\text{CO}}_{\text{3}}{{}^{\text{2-}}}_{\text{(aq)}}\stackrel{}{\to }{\text{CaCO}}_{\text{3(s)}}$

When two soluble solutions are mixed together, an insoluble salt formation occur so called precipitate. The precipitate obtained falls out of the solution and such reactions are called as precipitation reactions.