Neutralization reactions with gas formation

Many bases besides OH react with to form molecular compounds. Two of these that you might encounter in the laboratory are the sulfide ion and the carbonate ion. Both of these anions react with acids to form gases that have low solubilities in water. Hydrogen sulfide (H2S), the substance that gives rotten e s their foul odor, forms when an acid such as HCl(flq) reacts with a metal sulfide such as Na2S  

Carbonates and bicarbonates react with acids to form C02(g). Reaction of C03 or HC03 with an acid first gives carbonic acid (H2CO3). For example, when hydrochloric acid is added to sodium bicarbonate, the reaction is 

Carbonic acid is unstable. If present in solution in sufficient concentrations, it decomposes to H2O and CO2, which escapes from the solution as a gas  

The overall reaction is summarized by the equations Molecular equation  

Both NaHC03(s) and Na2C03(s) are used as neutralizers in acid spills, either salt is added until the fizzing caused by C02(g) formation stops. Sometimes sodium bicarbonate is used as an antacid to soothe an upset stomach. In that case the HC03 reacts with stomach acid to form C02(g). 

By analogy to examples given In the text, predict what gas forms when Na2S03(s) reacts with HCI(aq). 

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