how many molecules of water will be produced if 13.15g of pentane are burned

Question

this for chemistry 

Answer 1

Pentane has the formula C5H12.  The combustion of pentane is 

C5H12 + 8O2 ==> 5CO2 + 6H2O

moles of C5H12 used = 13.15 g x 1 mol/72.15 g = 0.1823 moles

moles of H2O formed from 0.1823 moles C5H12 = 0.1823 moles C5H12 x 6 moles H2O/moles C5H12 = 1.094 moles H2O 

molecules of water formed = 1.094 moles H2O x 6.02x10²³ molecules/mole = 6.586x10²³ molecules (4 significant figs)