ZnCl2 + NaOH = Zn(OH)2 + NaCl | Zinc Chloride + Sodium Hydroxide Reaction
Aqueous zinc chloride (ZnCl2) reacts with aqueous sodium hydroxide (NaOH) to produce zinc hydroxide ( Zn(OH)2 ) and sodium chloride (NaCl). Zinc hydroxide is a white colour precipitate and it is also an amphoteric hydroxide. Therefore, zinc hydroxide is dissolved when excess NaOH is added to the precipitate.
ZnCl2 + NaOH = Zn(OH)2 + NaCl
- Both zinc chloride (ZnCl2) and sodium hydroxide (NaOH) are colourless aqueous solution.
- When both solutions are mixed, a white colour precipitate, zinc hydroxide ( Zn(OH)2 ) is formed. In aqueous phase, there are sodium ions, chloride ions, little bit of Zn2+ ions and OH- ions.
Balanced equation of ZnCl2 + NaOH reaction
ZnCl2 + 2NaOH = Zn(OH)2 + 2NaCl
From the balanced equation, we can say, 1 mol of zinc chloride reacts with 2 mol of sodium hydroxide and produce 1 mol of zinc hydroxide and 2 mol of sodium chloride.
How to balance the ZnCl2 and NaOH reaction?
This equation can be balanced easily from following steps.
ZnCl2 + NaOH = Zn(OH)2 + NaCl
- There are two chlorine atoms in the left side. Therefore, to make two chlorine atoms in the right side, make two NaCl as below.
- ZnCl2 + NaOH = Zn(OH)2 + 2NaCl
- Now, there are two sodium atoms in the right side. To make two sodium in the left side, make two NaOH.
- ZnCl2 + 2NaOH = Zn(OH)2 + 2NaCl
ZnCl2 and excess NaOH
Remember that zinc is an amphoteric element and zinc hydroxide is an amphoteric hydroxide.
When aqueous NaOH is added to ZnCl2 solution drop by drop, at one time, Zn(OH)2 precipitate is formed. If you add more aqueous NaOH to the solution which contains the precipitate, precipitate is dissolved and give a colourless solution due to formation of sodium zincate (Na2ZnO2). Sodium zincate is a colourless aqueous solution.
Zn(OH)2 + 2NaOH → Na2ZnO2 + 2H2O
Sometime above equation is written as below.
Zn(OH)2 + 2NaOH → Na2[Zn(OH)4]
After dissolving Zn(OH)2 precipitate in the excess NaOH, what will happen if I add dilute HCl acid?
If you slowly add HCl acid to the [Zn(OH)4]2+, you can see a white precipitate is formed in the solution. That is zinc hydroxide precipitate. If you add more HCl acid, that white precipitate is also dissolved and give colourless ZnCl2 solution.
What will happen if little amount of ZnCl2 solution is added to large volume of aqueous NaOH?
Due to presence of excess NaOH, reaction will end up with soluble sodium zincate.
Questions asked by students
Ask your question and find the answer free.
What is the precipitate when zinc chloride and sodium hydroxide are mixed?
Zinc hydroxide is the given precipitate when Zinc chloride and Sodium hydroxide are mixed. But, if excess Sodium hydroxide is added, you will not see the formation of white precipitate because Zinc hydroxide is soluble in excess Sodium hydroxide. Similar to excess Sodium hydroxide case, if you use concentrated sodium hydroxide, there is the possibility of dissolving the Zinc hydroxide precipitate.
What are the other hydroxides except Sodium hydroxide, which can give Zinc hydroxide precipitate
Potassium hydroxide and Barium hydroxide are alternatives for Sodium hydroxide if you need to prepare Zinc hydroxide precipitate.
How do I decide whether a precipitate is formed or not when NaCl and ZnCl2 solutions are mixed with each other?
Option 1: If you know the concentratins of each solution, you can do a calculation to check Ksp value related to the Zn(OH)2.
In the final solution, if [Zn2+] * [Cl-]2 exceeds Ksp of Zn(OH)2, a precipiates is formed. When [Zn2+] and [Cl-] are taken, you should assume that there is no precipiate and all Zn2+ and Cl- ions exist in aqueous solution.
In the laboratory, I want to try this experiment. But, I could not find ZnCl2 in the lab. However, there was ZnO and other common chemicals. How do I do the experiment from ZnO?
You can do the experiment by starting from ZnO. Find dilute HCl bottle. Remember that it is good to use solid ZnO to prevent any impurities. Measure the weight ZnO and put it in a beaker. Then slowly add dilute HCl solution until all ZnO is dissolved. When all ZnO is dissolveed, ZnCl2 solution is given as the following reaction.
ZnO + 2HCl → ZnCl2 + H2O
Now, you can continue the rest of the experiment with by adding NaOH to ZnCl2 solution.
