Ferrous hydroxide (Iron(II) hydroxide) and Hydrochloric acid Reaction | Fe(OH)2 + HCl

Ferrous hydroxide (Fe(OH)2) reacts with hydrochloric acid (HCl) and form ferrous chloride (FeCl2) and water (H2O). This reaction is a weak base - strong acid reaction. Fe(OH)2 is a green colour precipitate and HCl is a colourless aqueous solution with strong acidic characteristics. When reaction occurs, the green colour precipitate is dissolved and a green colour solution is given.



In this tutorial, we will discuss followings.

Reaction of Fe(OH)2 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 Fe(OH)2, HCl and FeCl2


Reaction of Fe(OH)2 and HCl and balanced equation

  • As mentioned earlier, ferrous chloride and water are given as products. Because Ferrous hydroxide's solubility is low in water, Fe(OH)2 partially dissociates to Fe2+ and OH- ions in water. Therefore there is very low OH- concentration in the aqueous solution which contains Fe(OH)2.
  • But, HCl is readily soluble in water dissociates to H+ ions and Cl- ions and form a colourless solution.
  • Now, there are H+ ions and OH- ions in the solution due to the dissociation of Fe(OH)2 and HCl acid respectively when both solutions are mixed.
  • So, now neutralization reaction takes place as the figured below.
Fe(OH)2 + HCl reaction

Balanced equation of Fe(OH)2 and HCl

Fe(OH)2(s) + 2HCl(aq) → FeCl2(aq) + 2H2O(l)

According to the balanced equation, one mole of Fe(OH)2 reacts with two mole of HCl and gives one mole of FeCl2 and two moles of H2O respectively.



balanced equation of ferrous hydroxide hydrochloric acid Fe(OH)2 + HCl reaction

Explanation of dissolving of Fe(OH)2 by the concept of Equilibrium

Initially there are limited OH- concentration in the Fe(OH)2 solution. When HCl acid is added, hydroxyl ions received from Fe(OH)2 and H+ ions which are received from HCl. Now both OH- ions and H+ ions react with each other. Then OH- concentration is reduced. According to the Le'chatalier principle, to keep the equilibrium (to minimize the effect to the equilibrium), more Fe(OH)2 is dissolved to release more OH- ions and Fe2+ ions.



Reactants of the reaction: Fe(OH)2 and HCl


Ferrous hydroxide / Iron(II) hydroxide / Fe(OH)2

Ferrous hydroxide is a green colour solid at room temperature and poorly soluble in water. There is a very less amount of OH- concentration in an aqueous solution which contain Fe(OH)2 precipitate.


Hydrochloric acid (HCl)

Hydrochloric acid is a strong acid and highly soluble in water. It dissociates completely to H+ and Cl- ions in water.



Products of the reaction: FeCl2 and H2O


Ferrous chloride / Iron(II) chloride / FeCl2

Ferrous chloride is a greenish white crystalline solid and soluble in water to form colourless to greenish aqueous solution according to the concentration of FeCl2.



Change of oxidation numbers

Oxidation numbers of atoms are not changed during the reaction. Therefore, this reaction is not a redox reaction. But, if FeCl2 can be oxidized to FeCl3 in the presence of oxygen gas. If this oxidiation takes place in the solution, you can see a colour change from green to yellow-brown due to formation of Fe3+ cations.



Physical and chemical observation of Fe(OH)2 and HCl reaction

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



Colour and physical state changes

  • Because Fe(OH)2's solubility is low is water (as many metal hydroxides in water), you can see a deposited greenish solid at the bottom of the solution. HCl is a colourless solution.
  • FeCl2 is soluble in water and give a colourless to greenish colour aqueous solution. Therefore, you can a dissolving of the precipitate.


pH Change

  • pH value of aqueous solution which contain Fe(OH)2 is above 7. So that solution is basic. But, not a strong base because Fe(OH)2 is poorly soluble in water.
  • As all of we know, HCl is a strong acid and show a pH value less than 7.


Heat Generation

Because, a neutralization reaction takes place, heat is generated and released. Therefore, this reaction is an exothermic reaction.



Safety, health hazards and environmental impacts due to Fe(OH)2, HCl and FeCl2

  • Fe(OH)2: Nonflammable
  • HCl: Corrosive, Acute toxic
  • FeCl2: Irritant, Corrosive


Have Questions?



If excess Fe(OH)2 is added to the Fe(OH)2 + HCl reaction, what will be the observations?

Excess quantity of Fe(OH)2 remains in the solution as the precipitate because there is no HCl to react.



When ferrous hydroxide reacts with hydrochloric acid, What will happen to the pH value of if ferrous hydroxide is added to hydrochloric acid solution?

Because hydrochloric acid solution is a strong acid, pH value will be less than seven. When, H+ ions are consumed when HCl reacts with Fe(OH)2, acidity of HCl solution is decreased. Therefore, pH value is increased.



Are there any gas release in Ferrous hydroxide and hydrochloric acid reaction?

There is no gas production in this reaction.







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