Explain the observations and write a balanced net ionic equation for the reactio

Question

Explain the observations and write a balanced net ionic equation for the reactions.

1. When 6 M NaOH is added drop-wise to a solution of ZnCl2, a white precipitate forms which dissolves to form a colorless solution as excess reagent is added.

2. When 6 M NH3 is added drop-wise to a solution of Zn(NO3)2,a white precipitate forms which dissolves to form a colorless solution as excess reagent is added.

3. When 6 M NaOH is added drop-wise to a solution of AlCl3,a white precipitate forms which dissolves to forms which dissolves when 6 M HCl is added.

Explanation / Answer

1. Zn reacts with NaOH to form ppt of Zn(OH)2

ZnCl2 + 2NaOH --> Zn(OH)2 + 2NaCl

While in excess of NaOH the following reaction occur, the zincate ion forms is soluble in water

Zn(OH)2 + 2 OH? ? Zn(OH)42-.

2. Zn reacts with ammonia solution to form ppt of Zn(OH)2

In the presence of excess NH3, Zn(OH)2 dissolves forming a tetra-amine complex

2NH4OH + Zn (NO3)2 --> Zn(OH)2 + NH4NO3

3. NaOH reacts with AlCl3 to form Al(OH)3 ppt, the ppt dissolves in presence of HCl to give back AlCl3 and H2O

3NaOH + ALCL3 --> 3 NaCl + Al(OH)3

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