Question

How many grams of

diphosphorus trioxide, P2O3, are
required to react completely with
2.25 moles H₂O?

P2O3 + 3H₂O → 2H3PO3

[?] g P₂03

Answer 1

the answer is 82.5 g P2O3

you can use stoichiometry to solve for this problem. you’re given 2.25 mol H2O and when you look at your chemical reaction, you can see there’s 3 moles of H2O (look at the coefficients) and do the mole ratio. so in the chemical reaction, there’s 1 mol P2O3 and 3 mol H2O. you get your moles with that and since you need it in grams, you need to convert it using the P2O3 molar mass.

Answer 2

From the coefficients of the equation, we know that for every 3 moles of water consumed, 1 mole of diphosphorus trioxide is consumed.

This means we need to find the mass of 0.75 moles of diphosphorus trioxide.

• The atomic mass of phosphorous is 30.973761998 g/mol.
• The atomic mass of oxygen is 15.9994 g/mol.

So, the formula mass of diphosphorus trioxide is:

• 2(30.973761998)+3(15.9994)=109.945723996 g/mol.

Thus, 0.75 moles have a mass of:

• 0.75(109.945723996), which is about 82.5 g (to 3 sf)