Question

For the following reaction, 5.29 grams of water are mixed with excess diphosphorus pentoxide . The reaction yields 13.3 grams of phosphoric acid . diphosphorus pentoxide(s) + water(l) phosphoric acid(aq) What is the theoretical yield of phosphoric acid? grams What is the percent yield for this reaction? %

Answer 1

Given mass of water=5.29 g and molar mass of water=18 g/mol

Therefore moles of water=mass/molar mass=5.29 g/18 g/mol=0.2939 mol.

Diphosphorus pentoxide, P2O5 is an emperical formula and it exists as a dimer, P4O10.

The balanced reaction is

P4O10 + 6H2O --------> 4H3PO4

So moles of phosphoric acid formed=(4/6) moles of water (Since P4O10 is excess and water is limiting reacgent)

moles of H3PO4=(4/6) x 0.2939 mol=0.1959 mol.

Molar mass of phosporic acid=97.994 g/mol.

Therefore theoretical yield of H3PO4=moles x molar mass=0.1959 mol x 97.994 g/mol

Theoretical yield of H3PO4=19.199 g.

But experimental mass of H3PO4=13.3 g.

Therefore % yield=(experimental mass/theoretical mass)x100

% yield=(13.3g/19.199 g)x100=69.27 %.

Please let me know if you have any doubt.