Verification of phosphate with ammonium molybdate

Chemicals needed

distilled water

ammonium molybdate solution

sodium phosphate

nitric acid 13% C    R 34     S (1/2)-23-26-27

Equipment needed

test tube
burner (preferably alcohol-)

Test procedure

• Safety goggles!
• One adds a spatula-tipful of sodium phosphate and dissolves this with about 1 ml of diluted nitric acid.
• One adds some drops of ammonium molybdate solution and heats the mixture with the burner (caution!) until a yellow coloration occurs, whereby one should take care that the solution does not come to a boil.
• During cooling a yellow ammonium molybdophosphate precipitates. If this should not occur, one adds a little more ammonium molybdate solution and reheats.

Disposal

• The diluted reactive mixture can be disposed of into the drainage.

Elucidation

Ammonium molybdate forms with phosphate a complex salt which is insoluble and therefore precipitates

(NH4)3[P(Mo3O10)4]-ammonium molybdophosphate (correctly: ammonium dodeka molybdophosphate)

Photos

Precipitation of ammonium molybdophosphate

Literature

derived from experiment F.13.1, S.66, [4]