Wo3+3h2--> w+ many grams of tungsten trioxide must you start with to prepare 5.10g of tungsten? mw=231.8 amu

Add all the grams up then subtract 5.10 grams from your total

The balanced chemical reaction:

WO3+3H2-->W+3H2O

We are given the amount of tungsten trioxide to be used in the given reaction. This will be the starting point for our calculations.

5.10 g WO3 (1 mol W / 183.84 g W) ( 1 mol WO3 / 1 mol W ) ( 231.8 g WO3 /1 mol WO3 ) = 6. 43 g WO3 

The molecules contain like 54 of water 

1) according to the law of conservation of mass ,in all chemical reactions total mass is unchanged