Net Ionic Equations What They Are and How to Write Them

9-4 Net Ionic Equations What They Are and How to Write Them 

In Section 8.9 we showed how to write the double-replacement equation for a precipitation reaction between solutions of two ionic compounds. Such a reaction occurs when a solution of lead(II) nitrate is added to a solution of sodium chloride  

In this chapter we call this kind of equation a conventional equation. 

A conventional equation serves many useful purposes, including its essential role in understanding quantity relationships in chemical change. However, it falls short in describing precisely the reaction that occurs in water solution. Usually, it does not describe the reactants or products correctly. Rarely does it describe accurately the chemical changes that occur. 

The shortcomings of a conventional equation are illushated by this fact The solutions that react in Equation 9.1 contain no substances with the formulas Pb(N03)2 or NaCl. Actually present are the major species, Pb + and NO3 in one solution and Na and Cl in the other. The conventional equation doesn t tell you that. Nothing with the formula NaN03 is formed in the reaction. The Na and NO3 ions are still there after the reaction. The conventional equation kept that a secret, too. The only substance in Equation 9.1 that is really there is solid lead(H) chloride, PbCljCs). If you perform the reaction you can see the precipitate (Eig. 9.7). 

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