Phosphoric acid, H3PO4, has some important applications. It can be used to produce fertilizers and it is present in soft drinks. Phosphoric acid can be made from phosphorus in a two step process:

Question

Reaction 1: P4 + 5 O2 --> P4O10
Reaction 2: P4H10 + 6H2O--> 4H3PO4

A synthesis yielded 229g of H3PO4. How many moles of H3PO4 were produced?

Answer 1

I figured that out but I need help with this one:

How many moles of P4 would be required to produce the number of moles of H3PO4 determined from the question above which the answer is 2.34 for above.

Answer 2

Use the coefficients in the balanced equations to convert any value to any other value. In this case,
2.34 mol H3PO4 x (1 mol P4O10/4 mol H3PO4) x (1 mol P4/1 mol P4O10). Note how the unit cancel. The P4O10 cancels, and the H3PO4 cancels to leave what you want that looks like this.
2.34 x 1/4 x 1 mol P4 = (2.34/4) mol P4. You wanted mols P4.