Double-Replacement Reactions That Form Unstable Products

9-9 Double-Replacement Reactions That Form Unstable Products 

10 Given reactants that form H2CO3, H2SO3, or NH4OH by ion combination, write the net ionic equation for the reaction. 

Three ion combinations yield molecular products that are not the products you would expect. Two of the expected products are carbonic and sulfurous acids. If hydrogen ions from one reactant react with carbonate ions from another, carbonic acid, H2CO3, should form  

But carbonic acid is unstable and decomposes to carbon dioxide gas and water. The correct net ionic equation is therefore 

Sulfurous acid, H2SO3, decomposes in the same way to sulfur dioxide and water, but the sulfur dioxide remains in solution  

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