Stoichiometry please help?

Question

Phosphorus reacts with oxygen to form tetraphorus decoxide.How many grams of tetraphorus decoxide can be made from 3.5g. of phosphorus?

Answer 1

Balanced equation is:

4P + 5O2 ---> P4O10

Calculate moles of P in 3.5g:

3.5g P x 1mol/30.97g = 0.11mol

You get 1 mole of P4O10 for every 4 moles of P used, so:

0.11mol P x 1mol P4O10/4 mol P = 0.0275 mol P4O10

Calculate grams of P4O10 in 0.0275 moles:

0.0275 mol x 283.88g/mol = 7.81 g P4O10