Sodium nitrite and Hydrochloric acid Reaction | NaNO2 + HCl

Aqueous sodium nitrite (NaNO2) reacts with cold dilute hydrochloric acid (HCl) and gives nitrous acid (HNO2) and sodium chloride (NaCl). This reaction is used to prepare nitrous acid. But, If HCl acid is added to solid NaNO, nitrogen dioxide (NO2) gas is emitted.



In this tutorial, we will discuss followings.

Reaction of aqueous NaNO2 and HCl and balanced equation Reaction of solid state NaNO2 and HCl and balanced equation Reactants of reactions Products of reactions Change of oxidation numbers Physical and chemical properties changes during the reaction Health, safety measures of NaNO2, HCl, HNO2 and NO2


Reaction of aqueous NaNO2 and aqueous HCl and balanced equation


NaNO2(aq) + HCl(aq) → NaCl(aq) + HNO2(aq)

Slowly add cold dilute HCl acid to the aqueous NaNO2 solution. All reactants and products are in aqueous state. According to the balanced equation, one mole of NaNO2 reacts with one mole of HCl and gives one mole of NaCl and one mole of HNO2 respectively.



aqueous sodium nitrite and hydrochloric acid reaction - NaNO2 + HCl

Reaction of solid form NaNO2 and HCl

When, a metal nitrite compound (in solid state) met a dilute acid (such as HCl, H2SO4), brown colour nitrogen dioxide (NO2) gas is evolved. So, when dilute HCl acid is added to solid state NaNO2, nitrogen dioxide is evolved. As other products, NaCl, NO and H2O are given.

2NaNO2(aq) + 2HCl(aq) → 2NaCl(aq) + NO2(g) + NO(g) + H2O(l)


Reactants of reaction


Sodium nitrite (NaNO2)

Sodium nitrite is soluble in water and form a colourless solution. Sodium nitrite is prepared by heating of solid sodium nitrate.


Hydrochloric acid

Hydrochloric acid is a very common strong acid and it readily dissociates to H+ and Cl- ions in water. These Hydrochloric acid solutions show pH values much less than 7 due to its strong acidic nature.



Products of reaction


Nitrous acid (HNO2)

HNO2 is a weak, unstable inorganic acid. It readily decomposes to nitric acid (HNO3), nitric oxide (NO) and water.


Sodium chloride (NaCl)

Sodium chloride is a white solid at room temperature and highly soluble in water.



Change of oxidation numbers

Considering aqueous NaNO2 and HCl reaction

This reaction is not a redox reaction because oxidation numbers of atoms are not changed during the reaction.



Considering solid form NaNO2 and HCl reaction

This reaction is a redox reaction because oxidation numbers of nitrogen atoms are changed during the reaction. In NaNO2, nitrogen's oxidation number is +3. During the reaction, NO2 gas and NO are given. Nitrogen atom are at +4 and +2 oxidation state in NO2 and NO respectively. So, you can understand this reaction is a disproportionation reaction.





Physical and chemical observation of NaNO2 and HCl reaction

Here, we will see some physical observations and chemical properties changes during the reaction.


Colour and physical state changes

Because there are two possible reactions, we will consider both reactions separately.


Aqueous NaNO2 and HCl reaction

  • As mentioned earlier, Sodium nitrite (NaNO2CO) is highly soluble in water form a colourless aqueous solution. Aqueous hydrochloric acid (HCl) is a colourless solution.
  • Aqueous solution which contain both of NaCl and HNO2 is light blue liquid due to HNO2. Otherwise ore NaCl aqueous solution is a colourless solution.

Solid form NaNO2 and HCl reaction

  • When HCl acid is added to solid form NaNO2, brown colour NO2 gas is emitted.


pH change

  • Reactants: Considering NaNO2 aqueous solution, NO2- ion is not stable in water and participate in hydrolysis reaction to form hydroxyl ions. Therefore, NaNO2 solution may show pH value just above 7.
    • But HCl is strong acid and should show pH value less than 7.
  • Products: NaCl and HNO2 mixture: NaCl is stable in water and do not participate in hydrolysis action. But HNO2 is a weak acid and show pH value less than seven.


Safety, health hazards and environmental impacts due to NaNO2, HCl, HNO2

  • HCl: You should be extremely careful when diluted HCl solution is prepared by concentrated HCl becauase HCl vapour can harm eyes and skin. Also, it is toxic if inhaled. Serious skin burns are possible and wear personal protective equipments (PPEs) always using this chemical.
  • NaNO2: Very toxic to aquatic life, Toxic if swallowed, may intensify fire;.
  • HNO2: Fatal if swallowed, Causes severe skin burns and eye damage
  • NO2: Fatal if inhaled, serious eye damages, severe skin burns and eye damage, cause acid rains


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