Aqueous solution of sodium hydroxide can be used to test for the presence of : I. Ca\(^{2+}\) , II. Zn\(^{2+}\) , III. Cu\(^{2+}\)
- I only
- I and III
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I, II and III
- I and II only
The correct answer is: C
Explanation
An aqueous solution of sodium hydroxide (NaOH) can be used to test for metal cations, such as: Aluminum (Al), Calcium (Ca), Copper (II) (Cu),Iron (II) (Fe), Iron (III) (Fe), Magnesium (Mg), Zinc (Zn) etc.
Sodium hydroxide solution is a useful base for identifying ionic metal compounds because it reacts with metallic ions. The color of the precipitates formed and their solubility in excess of the reagent can help identify cations in aqueous solutions.
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Calcium ions: A few drops of dilute sodium hydroxide solution will form a white precipitate with calcium ions. Adding excess sodium hydroxide solution will not change the precipitate.
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Zinc ions: A few drops of dilute sodium hydroxide solution will form a white precipitate with zinc ions. Adding excess sodium hydroxide solution will dissolve the zinc hydroxide precipitate to form a colorless solution.
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Copper ions: Sodium hydroxide solution will form a blue precipitate with copper(II) ions.
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