Question

What would be the observations when aqueous ammonia is added to a solution of zinc nitrate (until in excess) and heated?
A.White precipitate formed. On heating, a colourless, pungent gas evolved.
B.White precipitate formed which dissolved in excess aqueous ammonia to form a colourless solution.
C.White precipitate formed which dissolved in excess aqueous ammonia to form a colourless solution. On heating, a colourless, pungent gas evolved.
D.Blue precipitate formed which dissolved in excess aqueous ammonia to form a dark blue solution. On heating, a colourless, pungent gas evolved.

Answer 1

Hint:This may be a typical antacid reaction wherein the soluble base responds with a metal salt to give a metal hydroxide and the eventual outcomes rely upon whether smelling salts is in abundance. In the event that it is, a further response happens.

Complete answer:
The alkali, being a feeble base, produces hydroxide particles in the water.
$Z{n_{2(aq)}} + 2O{H^ - }_{(aq)} \to Zn{(OH)_{2(s)}}$
The zinc hydroxide is the white encourage.
In the event that you keep on adding the alkali arrangement the encourage re-dissolves due to the development of the solvent particle $Zn{(N{H_3})_4}$ to give a drab arrangement. At the point when heated ammonia gas is developed which is pungent in smell.

So, option(C) White precipitate formed which dissolved in excess aqueous ammonia to form a colourless solution. On heating, a colourless, pungent gas evolved is the correct answer.

Note:
A substantial white amorphous powder $(N{H_2}.HgCl)$ got by adding alkali to an answer of mercuric chloride or destructive sublimate; - in the past called additionally infusible white encourage, and now amido-mercuric chloride.
A white translucent substance acquired by adding an answer of destructive sublimate to a solution of sal ammoniac (ammonium chloride); - earlier called likewise fusible white precipitate.
Aluminium, zinc and lead (II) ions give white precipitate with a couple of drops of aqueous ammonia. In the event that the precipitate dissolves in excess to shape a colourless solution, at that point zinc ion is available. If the precipitate remains insoluble in excess fluid smelling salts, aluminium ion or lead (II) ions could be available. Further tests should be possible to recognize which of these two ions are available.