Please Help W/ Chemistry Question!

Question

Consider the reaction of hydrogen and oxygen producing water. If 24.6 g of water is produced and 2.9 g of hydrogen is used, how many g of oxygen are needed?

 

Is it 27.5? Or am I wrong and overthinking. 

Answer 1

To answer this question you need to write a balanced chemical reaction:

 

2 H₂(g) + O₂(g) → 2 H₂O(l)

 

We can calculate the mass of O₂ needed to form 24.6 g H₂O based on the stoichiometry of the reaction:

 

24.6 g H₂O x (1 mol H₂O/18 g H₂O) x (1 mol O₂/2 mol H₂O) x (32.00 g O₂ /1 mol O₂) = 21.87 g O₂

 

You can also verify that H2 is in excess in the reaction based on the stoichiometry of the reaction:

24.6 g H₂O x (1 mol H₂O/18 g H₂O) x (2 mol H₂/2 mol H₂O) x (2.016 g H₂ /1 mol H₂) = 2.76 g H₂  

 

The mass of H₂ needed is less than the real mass added at the beginning (2.9 g). This confirms that H₂  is in excess.

Answer 2

amount should be 21.87g