Ferrous 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 aqueous solution. When reaction occurs, green colour precipitate is dissolved and green colour solution is given.

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In this tutorial, we will discuss followings.

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 due to dissociation of Ca(OH)2 and HCl when both solutions are mixed. So, now neutralization reaction takes place as figured below.

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.

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

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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 a 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.

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, 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.

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.

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

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Questions

Ask your chemistry questions and find the answers

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

Becase 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.

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