Question

When a mixture containing phosphate is heated with conc.$HN{O_3}$ and ammonium molybdate solution, a canary yellow precipitate is formed. The formula of the yellow precipitate is:

Answer 1

Hint: Nitric acid is a strongly corrosive mineral acid commonly known as aqua fortis and spirit of niter. The pure compound is colourless, but decomposition into nitrogen oxides and water causes older samples to turn yellow. In water, the majority of commercially available nitric acid has a concentration of 68 percent.

Complete answer: The inorganic compound ammonium heptamolybdate has the chemical formula ${\left( {{\text{N}}{{\text{H}}_4}} \right)_6}{\text{M}}{{\text{o}}_7}{{\text{O}}_{24}}$and is typically used as a tetrahydrate. It's also known as a dihydrate. It's a colourless solid that goes by the names ammonium paramolybdate or simply ammonium molybdate, while "ammonium molybdate" may also apply to ammonium orthomolybdate,${\left( {{\text{N}}{{\text{H}}_4}} \right)_2}{\text{Mo}}{{\text{O}}_4}$, and a variety of other compounds. It's a molybdenum compound that's very popular.
Canary Yellow has a chartreuse undertone and is a midtone, shiny, glowing firefly yellow-green.
A canary yellow crystalline precipitate of ammonium phosphomolybdate (ammonium dodecamolybdatophosphate)${\left( {{\mathbf{N}}{{\mathbf{H}}_4}} \right)_3}\left[ {{\mathbf{PM}}{{\mathbf{o}}_{12}}{{\mathbf{O}}_{40}}} \right]{\text{ or }}{\left( {{\mathbf{N}}{{\mathbf{H}}_4}} \right)_3}\left[ {{\mathbf{P}}{{\left( {{\mathbf{M}}{{\mathbf{o}}_3}{{\mathbf{O}}_{10}}} \right)}_4}} \right]$ is formed when ammonium molybdate is treated with a phosphate solution.
Each oxygen atom in phosphate is replaced by the${\text{M}}{{\text{o}}_3}{{\text{O}}_{10}}$ group in the resulting compound.
${\text{PO}}_4^{3 - } + {\mathbf{3}}{\text{NH}}_4^ + + 12{\text{MoO}}_4^{2 - } + {\mathbf{24}}{{\mathbf{H}}^ + } \to {\left( {{\mathbf{N}}{{\mathbf{H}}_4}} \right)_3}\left[ {{\mathbf{P}}{{\left( {{\text{M}}{{\text{o}}_3}{{\text{O}}_{10}}} \right)}_4}} \right] \downarrow + {\mathbf{12}}{{\text{H}}_2}{\text{O}}$
The inorganic salt of phosphomolybdic acid, ammonium phosphomolybdate, has the chemical formula ${\left( {{\text{N}}{{\text{H}}_4}} \right)_3}{\text{PM}}{{\text{o}}_{12}}{{\text{O}}_{40}}$. The phosphomolybdate ion complex is contained within it.
Heat ammonium orthomolybdate, phosphoric acid, and nitric acid together to produce ammonium nitrate, water, and a yellow precipitate of ammonium phosphomolybdate.

Note:
For a variety of reasons, nitric acid is the preferred solution. It's an oxidising acid capable of dissolving most metals and forming soluble metal nitrates. The exciting part about Aqua Regia is that none of the two acids will remove gold on their own. Nitric acid doesn't react well with gold, and HCl, or hydrogen chloric acid, can't get a hold of it to initiate the reaction.