Qualitative analysis (identification) of Zinc (Zn2+) cation,part 02
Salts are compounds which are formed from the reaction between acids and bases. An inorganic salt is just a salt which has no organic part in its molecular structure. Any salt is composed of two parts – cation and anion. The cation part usually comes from the base and the anion part usually comes from the acid.
Based on solubility characteristics, the common inorganic cations (usually metal in nature) are classified into five groups. Cations of each group is precipitated a common reagent. So, by step-wise addition of those reagents, we can first identify which group the cation belongs to. Then by using specific reagents we can confirm the cation.
The common inorganic cations can be classified into five groups based on solubility characteristics. Cations of each class are precipitated by a specific reagent.
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When dilute sodium hydroxide is added to a solution containing zinc ions (Zn2+), a gelatinous white precipitate is formed.
Addition of concentrated sodium hydroxide (excess dil. NaOH) produces a soluble complex resulting in a clear solution.
Or, Zn(OH)2 + 2NaOH Na2ZnO2 +2H2O
Soluble Complex
Addition of H2S in this solution results in the formation of a white PPT due to the formation of
ZnS.
