Single Choice

A reddish-pink substance on.heating gives off a vapor which condenses on the sides of the test tube and the substance turns blue. If on cooling water is added to the residue, it turns to its original color. The substance is :

Alodine crystals
BCopper sulphate crystals
CCobalt chloride crystals
Correct Answer
DZinc oxide

Solution

Option (C) is correct.
The substance is cobalt chloride crystals.It is a property of $$CoCl_2$$.
Cobalt sulphide dissolves in aqua regia in the same manner as nickel sulphide. When the aqueous solution of the residue obtained after treatment with aquaregia is treated with a strong solution of potassium nitrite after neutralisation with ammonium hydroxide and the solution is acidified with dil. acetic acid, a yellow precipitate of the complex of cobalt named potassium hexanitritocobaltate (III) is formed.

$$CoS + HNO_3 + 3HCl \longrightarrow CoCl_2

+ NOCl + S + 2H_2O$$
$$ CoCl_2

+ 7KNO_2 + 2CH_3COOH \longrightarrow K_3 [Co(NO_2)_ 6] + 2KCl + 2CH_3COOK + NO + H_2O$$

SIMILAR QUESTIONS

Chemistry Practical

The cation that will not be precipitated by $$H$$_2S$$ in the presence of dil $$HCl$$ is:

Chemistry Practical

A solution containing a group-IV cation gives a precipitate on passing $$H_2S$$. A solution of this precipitate in $$dil.HCl$$ produces a white precipitate with basic $$NaOH$$ solution and bluish-white precipitate with basic potassium ferrocyanide. The cation is:

Chemistry Practical

In Nessler's reagent for the detection of ammonia the active species is:

Chemistry Practical

Reagent used in the qualitative analysis of IVth group is

Chemistry Practical

Group reagent for analytic group $$IV$$ is

Chemistry Practical

Precipitate of group $$IV$$ cations takes place when $$H_2S$$ is

Chemistry Practical

In $$IV$$ group analysis, $$NH_{4}OH$$ is added before passing $$H_{2}S$$ gas because:

Chemistry Practical

Mark the correct statement(s)

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