Aqueous ferrous chloride (FeCl2) reacts with aqueous sodium hydroxide NaOH to produce ferrous hydroxide Fe(OH)2 and sodium chloride (NaCl). Color changes, precipitating, balanced reaction, ionic equation of FeCl2 + NaOH reaction are discussed in this tutorial.
written by: Heshan Nipuna, updated on: 26/05/2020
Sodium hydroxide is a strong alkaline colorless solution.
Above reaction is not a balanced chemical reaction. Therefore, you need to balance this reaction and we will do it in next section.
This reaction is a not a redox reaction. Therefore by observing number of atoms in right side and left side, we can balance the reaction in few seconds.
According to the stoichiometry of the reaction, 1 mol of FeCl2 reacts with 2 mol of NaOH and produce 1 mol of Fe(OH)2 and 2 mol of NaCl.
Solubility of Fe(OH)2 is poor in water. Hence it deposits as a precipitate.
Fe(OH)2 is easily oxidized to Fe(OH)3 by oxygen gas. Therefore, green color of the precipitate will be changed to reddish brown when Fe(OH)3 is formed.
Questions asked by students
Whether NaOH concentration is low, if ferrous ion concentration is high, Fe(OH)2 precipitate will be formed due to having enough concentrations of ions to exceed solubility product.
Fe2+ + OH- → Fe(OH)2
Fe(OH)2 is not soluble in excess NaOH or aqueous ammonia solution.
If we can give Fe2+ ion to the NaOH solution, Fe(OH)2 precipitate can be formed. To give Fe2+ ions, soluble Fe2+ compound should be used. Therefore, FeSO4, Fe(NO3)2 can be used as compounds. FeCO3 cannot be used because it is insoluble in water and gives very low Fe2+ ion concentration too.
In the presence of oxygen gas, Fe2+ ions readily oxidizes to Fe3+ ions. That's why green color of Fe(OH)2 is tuned to brown color of Fe(OH)3.
This is not a single step work. You have to do some reactions.