[Sciencelover12]

Hello!

I would like to know if someone could tell me if that is right:
4 H+ + 4 e− + O2 → 2 H2O

Q:How many grams of H have to react, in order to get 90g of H20?


My solution: 

Ratio: 4:2

=>   First "translate" H20 into moles:   90/18=5 moles

now, I created an equation, where x stands for grams of H:  x* (1mol/4g H) = 5 mole

x=> 20.

now, we have two molecules of H20, which is why we have to divide 20/2, giving 10g of H.

Is that right?

[Borek]

I am not sure I understand the logic behind your calculations.

an equation, where x stands for grams of H:  x* (1mol/4g H) = 5 mole

is probably wrong in some way, and the error cancels out when you divide the result by two, but 10 g is OK.

[Sciencelover12]

Well, how do you calculate it normally then ?

[Borek]

Google for worked out examples of stoichiometry calculations, plenty of examples and tutorials on the web.

Like this one: http://www.chembuddy.com/?left=balancing-stoichiometry&right=toc