How do I compute mass of product (O₂) from mass of reactant (KClO₃)?

50.0 g of potassium chlorate is decomposed by heating. What is the mass of O₂ prepared?

1. Calculate moles of KClO₃ decomposed. To convert grams to moles, use the molecular weight of the compound:

   50.0 g KClO3 ×

   1 mol KClO3 122.6 g KClO3

   = 0.408 mol KClO3

2. Calculate moles of O₂ prepared. To convert moles of one substance to moles of another, you need a balanced chemical equation that relates them. In this case, it's 2 KClO₃ 2 KCl + 3 O₂ The coefficients in the equation give the mole-to-mole conversion factor:

   0.408 mol KClO3 ×

   3 mol O2 1 mol KClO3

   = 0.610 mol O2

3. Calculate the mass of O₂ prepared. Again, to convert moles to grams, use the molecular weight of the compound:

   = 0.610 mol O2

   32.0 g O2 1 mol O2

   = 19.6 g O2

Author: Fred Senese senese@antoine.frostburg.edu

Copyright © 1997-2010 by Fred Senese
Comments & questions to fsenese@frostburg.edu
Last Revised 02/23/18.URL: http://antoine.frostburg.edu/chem/senese/101/moles/faq/stoichiometry-o2-from-kclo3.shtml