Chemistry Problem?

[匿名]

2017-10-29 11:00 pm

1) You have an unknown cation (one of the ten from this experiment). Your solution is colorless and odorless. Treatment with HCl produces no observable change. Treatment with NaOH produces a white gelatinous precipitate that dissolves in excess NH3. Treatment with NaOH also produces a white gelatinous precipitate which dissolves in excess NaOH. What is the identity of your cation?

2) Write net ionic equations for the reactions as described in Question #1. (Note: You should have four equations)

回答 (1)

wanszeto

2017-10-29 11:09 pm

1)
It is zinc ion, Zn²⁺ ion.

This is because zinc ion does not react with HCl. Zinc ion reacts with NH₃ to form white gelatinous precipitate of Zn(OH)₂, which dissolves in excess NH₃. Zinc ion also reacts with NaOH to form a white gelatinous precipitate of Zn(OH)₂, which dissolves in excess NaOH.

2.
Zinc ion reacts with NH₃ to form white gelatinous precipitate of Zn(OH)₂, which dissolves in excess NH₃.
NH₃(aq) + H₂O(l) ⇌ NH₄⁺(aq) + OH⁻(aq)
Zn²⁺(aq) + 2OH⁻(aq) → Zn(OH)₂(s)
Zn(OH)₂(s) + 4NH₃(aq) → [Zn(NH₃)₄]²⁺(aq) + 2OH⁻(aq)

Zinc ion also reacts with NaOH to form a white gelatinous precipitate of Zn(OH)₂, which dissolves in excess NaOH.
Zn²⁺(aq) + 2OH⁻(aq) → Zn(OH)₂(s)
Zn(OH)₂(s) + 2OH⁻(aq) → [Zn(OH)₄]²⁻(aq)

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