Question

What do you observe when sodium hydroxide solution is added to zinc sulphate solution in excess?

Answer 1

About double displacement reaction:

• The reaction in which two different ions in the reactant molecules are displaced by each other, to form two new compounds is called a double displacement reaction.
• A double displacement reaction is also known as a double decomposition reaction.
  

When sodium hydroxide solution is put in zinc sulfate solution in excess:

• when sodium hydroxide is added dropwise until in excess to a solution of zinc sulfate it is observed that white precipitate is formed which is soluble in excess of sodium hydroxide. This is an example of a double displacement reaction.
• Reaction:

$$\begin{gathered} \underset{Zincsulphate}{ZnS{o}_4\left(s\right)}+\underset{Sodiumhydroxide}{2NaOH\left(aq\right)}\to \underset{Zinchydroxide}{Zn{\left(OH\right)}_2\left(s\right)}+\underset{Sodiumsulfate}{N{a}_{2}S{O}_4\left(s\right)} \\ \underset{Zinchydroxide}{Zn{\left(OH\right)}_2\left(s\right)}+\underset{Sodiumhydroxide}{2NaOH\left(aq\right)}\to \underset{Sodiumzincate}{N{a}_{2}Zn{O}_2\left(s\right)}+\underset{Water}{2H_{2}O\left(l\right)} \end{gathered}$$