Nickel chloride (NiCl2) and sodium hydroxide (NaOH) reacts and gives green colour nickel hydroxide (Ni(OH)2) precipitate and sodium chloride (NaCl). Nickel chloride is a green colour solution and sodium chloride is colourless aqueous solution. However, nickel hydroxide is not soluble in excess NaOH.
Aqueous nickel chloride is a green colour solution and aqueous sodium hydroxide is a colourless solution. When they react with each other, green colour precipitate, nickel hydroxide and colourless sodium chloride solution is given.
1 mol of NiCl2 reacts with 2 mol of NaOH and produce 1 mol of Ni(OH)2 and 2 mol of NaCl. Except Ni(OH)2, all other compounds exist as aqueous state. Ni(OH)2 exists in solid state.
When you are slowly adding one chemical to other chemical drop by drop, at one time, you will see a green colour precipitate is formed in the solution. If you suddenly add one chemical to another, green precipitate is also formed immediately.
Nickel hydroxide is not soluble in excess sodium hydroxide because nickel hydroxide is not a amphoteric hydroxide. Therefore, nickel hydroxide precipitate will remain as the green precipitate when NaOH is added more and more.
We know, aqueous NaOH has high pH values because NaOH is a strong base. When NiCl2 is added, OH- ions are reduced in the aqueous solution because OH- ions are combined with Ni2+ and get deposited as a precipitated. Due to reduction of OH- ion concentration, pH value is decreased.
Questions asked by students
Both aqueous NiCl2 and queous FeCl2 are green colour solutions. Both these compounds react with NaOH and give green colour precipitates (respective metal hydroxides) and they are insoluble in excess NaOH. Therefore we cannot identify NiCl2 and FeCl2 by NaOH.
Yes. you see. Because solid NiCl2 dissociates to nickel +2 ions and chloride ions in water. Then, nickel +2 ion and hydroxyl ions form nickel hydroxide precipitate.