How to Prepare Ammonium Molybdate: 1N and 0.5N

Ammonium Molybdate: 

1. Preparation of 0.5M, 1 N.

Mix well 72 g of pure MoO5 (or 81 g of H2MoO4) with 200 ml of water, and add 60 ml of conc. ammonium hydroxide. When solution is complete, filter and pour filtrate, very slowly and with rapid stirring, into a mixture of 270 ml of conc. HNO3 and 400 ml of water. Allow to stand over night, filter and dilute to 1 liter.

2. The reagent is prepared as two solutions which are mixed as needed, thus always providing fresh reagent of proper strength and composition. Since ammonium molybdate is an expensive reagent, and since an acid solution of this reagent as usually prepared keeps for only a few days, the method proposed will avoid loss of reagent and provide more certain results for quantitative work.

Solution 1: 

Dissolve 100 g of ammonium molybdate (C.P. grade) in 400 ml of water and 80 ml of 15 M NH4OH. Filter if necessary, though this seldom has to be done

Solution 2: 

Mix 400 ml of 16 M nitric acid with 600 ml of water.

For use, mix the calculated amount of solution 1 with twice its volume of solution 2, adding solution 1 to solution 2 slowly with vigorous stirring. Thus, for amounts of phosphorus up to 20 mg, 10 ml of solution 1 to 20 ml of solution 2 is adequate. Increase amount as needed.

Share