Why isn't nitrous acid a product of nitrite and water?


> 
> **Question**  
> 
>  Predict the products of the following acid-base reactions, and predict whether the equilibrium lies to the left or to the right of the equations
>  $$\ce{NO2- + H2O -> ?}$$
> 
> 
> 


I thought it would be $\ce{NO2- + H2O -> HNO2 + OH-}$, but my textbook says that the correct products are $\ce{HNO3}$ and $\ce{OH-}$. What am I doing wrong here? The answer that they give doesn't even seem to balance.




It should form nitrous acid... If it was $NO\_3^{-}$, nitrate ion, then it would presumably form nitric acid $HNO\_3$.


Nitrous acid reacts with water to form nitrite and hydronium:


$$\ce{HNO\_2 + H\_2O -> NO\_2^- + H\_3O^+} $$


Water is an amphoteric species. Assuming we just have water the nitrite ion, the nitrite ion accepts the hydrogen forming nitrous acid:


$$\ce{NO\_2^- + H\_2O -> HNO\_2 + OH^-} $$


This reaction is interesting as well since nitrous acid will also dissociate again into nitrite ions and water as well:


$$\ce{HNO\_2 + H\_2O -> NO\_2^- + H\_3O^+} $$


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It can be, since the $\ce{HNO2}$ is very unstable and decompose very easily (disproportioning): 
$$\ce{3HNO2 \rightarrow HNO3 + 2NO +H2O}$$


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