Thread: How many grams of CO2 and H2O do need to start with the end up with 20 grams of C6H12O2?

A little chem help please?

It's hard to imagine anything with the formula C6H12O2 being the product of a reaction of CO2 with H2O, but if you insist:

6 CO2 + 6 H2O ? C6H12O2 + 8 O2

(20 g C6H12O2) / (116.1589 g C6H12O2/mol) x (6/1) = 1.0331 moles each of CO2 and H2O

(1.0331 mol CO2) x (44.0096 g/mol) = 45 g CO2
(1.0331 mol H2O) x (18.0153 g/mol) = 19 g H2O

If the product were something more reasonable, like photosynthesis, then:
6 CO2 + 6 H2O ? C6H12O6 + 6 O2
and the calculations should be repeated after substituting 180.1566 g/mol for the molar mass of the product above, yielding:
29 g CO2 and 12 g H2O