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Addition of NaOH on Zn^(2+) ion gives a ...

Addition of NaOH on `Zn^(2+)` ion gives a white ppt. which on addition of excess of NaOH which dissolves . In this solution Zn exists in

A

`Zn^(2+)` form

B

Cationic form

C

Anionic form

D

Both (2) & (3)

Text Solution

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The correct Answer is:
### Step-by-Step Solution: 1. **Understanding the Reaction**: When sodium hydroxide (NaOH) is added to zinc ions (Zn²⁺), a white precipitate of zinc hydroxide (Zn(OH)₂) is formed. **Reaction**: \[ \text{Zn}^{2+} + 2 \text{NaOH} \rightarrow \text{Zn(OH)}_2 \, (\text{white precipitate}) \] **Hint**: Identify the ions and the precipitate formed when NaOH is added to Zn²⁺. 2. **Addition of Excess NaOH**: When excess NaOH is added to the white precipitate (Zn(OH)₂), it dissolves to form sodium zincate (Na₂ZnO₂). **Reaction**: \[ \text{Zn(OH)}_2 + 2 \text{NaOH} \rightarrow \text{Na}_2\text{ZnO}_2 + 2 \text{H}_2\text{O} \] **Hint**: Consider how excess NaOH affects the solubility of the precipitate. 3. **Formation of the Complex**: In solution, sodium zincate can exist as a complex ion. The zinc in this complex can be represented as \(\text{Zn(OH)}_4^{2-}\). **Complex Formation**: \[ \text{Na}_2\text{ZnO}_2 + \text{H}_2\text{O} \rightarrow \text{Na}_2\text{Zn(OH)}_4 \] **Hint**: Look for the coordination complex formed in the presence of hydroxide ions. 4. **Determining the Oxidation State**: In the complex \(\text{Zn(OH)}_4^{2-}\), zinc is in the +2 oxidation state, but the overall complex carries a -2 charge, indicating that zinc is acting as an anion in this context. **Conclusion**: - In the complex, zinc exists in an anionic form as \(\text{Zn(OH)}_4^{2-}\). - Therefore, the answer to the question is that zinc exists in an **anionic form** in this solution. **Final Answer**: Zinc exists in an anionic form.
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Knowledge Check

  • An inorganic compound (X) shows the following reactions : (a) It is white solid, exists as dimer and fumes in moist air. (b) It sublimes at 180^@ C and forms monomer on heating to 400^@ C . ( c) Its aqueous solution turns blue litmus red and gives a white precipitate with AgNO_(3) solution which is soluble in excess of NH_(4) OH . (d) Addition of NaOH to the solution of (A) gives a white gelatinous precipitate which is, however, soluble on excess of NaOH . Identify the compound (A) .

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