# 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's probably a typo. Nitrate is used very often and nitrite much less so. It's an easy mistake to make and a difficult one to catch. That's my best guess unless they give an answer of the type that @Matej suggests, though that seems to require quite a bit of insight into the chemistry for an AP Chem text. – Jason Patterson Nov 9 '14 at 15:17
• Can you recheck and clarify if the question gives you $\ce{NO2}$ or $\ce{NO2-}$? The sign makes a big difference. If you had $\ce{NO2}$ gas, then you will get both $\ce{HNO3}$ and $\ce{HNO2}$ ($\ce{HNO2}$ further undergoes disproportionation to give $\ce{HNO3}$ and $\ce{NO}$). – Yashas May 9 '17 at 15:22

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:

$$\ce{HNO_2 + H_2O -> NO_2^- + H_3O^+}$$

• I checked several times, the book says that the products are $\ce{HNO3}+\ce{OH-}$ – scrblnrd3 Mar 3 '14 at 1:34
• Chemistry, the Central Science, 11th AP Edition. Question is on page 711 – scrblnrd3 Mar 3 '14 at 1:44

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