In the electrolysis of water, how many grams of oxygen gas will be produced for every gram of hydrogen gas formed? Reaction: 2H2O(l) ===> 2H2(g) + O2(g)

Expert Answers
tjbrewer eNotes educator| Certified Educator

For every molecule of hydrogen gas produced, one molecule of oxygen will be produced.  This means that for every mole of oxygen produced, 2 moles of hydrogen will be produced.  However, the mass of one mole of hydrogen, is not the same as the mass of one mole of oxygen.  Since Hydrogen has an atomic mass of 1, every mole of Hydrogen has a mass of 1 gram.  The atomic mass of Oxygen is 16, so one mole of oxygen will have a mass of 16 grams.  So now we need to transpose ratios:

We want the ratio of oxygen mass:hyrdogen mass.  We know that Oxygen mol:Hydrogen mol=1:2 expressed as a fraction `1/2` We then convert Oxygen mol to oxygen mass by multiplying the ratio by the ratio of atomic mass to moles of oxygen `(1molO)/(2molH)xx(16gO)/(1molO)=(16gO)/(2molH)` We then multiply our ratio by the ratio of atomic mass to moles of hydrogen to convert hydrogen to mass`(16gO)/(2molH)xx(1molH)/(1gH)=(16gO)/(2gH)` We then reduce the fraction and we get `(8gO)/(1gH)` 8 grams of Oxygen to each gram of Hydrogen. 

jeew-m eNotes educator| Certified Educator

`2H_2O rarr 2H_2+O_2`


Mole ratio

`H_2:O_2 = 2:1`

Molar mass in grams

`H_2 = 2`

`O_2 = 32`


At the medium hydrogen is as `H_2` and Oxygen is as `O_2` .


Amount of `H_2 ` moles in 1g of Hydrogen `= 1/2`

Amount of `O_2` formed `= 1/2xx1/2 = 0.25`


Mass of `O_2 = 0.25xx32 = 8g`


So 8g of `O_2` gas will be formed for every 1g of `H_2` .