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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Sciencelover12 on November 29, 2017, 05:14:06 PM

Title: Stochiometry
Post by: Sciencelover12 on November 29, 2017, 05:14:06 PM
Hello!

I would like to know if someone could tell me if that is right:
4 H+ + 4 eāˆ’ + O2 ā†’ 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?
Title: Re: Stochiometry
Post by: Borek on November 29, 2017, 05:23:52 PM
I am not sure I understand the logic behind your calculations.

Quote from: Sciencelover12 on November 29, 2017, 05:14:06 PM
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.
Title: Re: Stoichiometry
Post by: Sciencelover12 on November 29, 2017, 05:36:15 PM
Well, how do you calculate it normally then ?
Title: Re: Stochiometry
Post by: Borek on November 30, 2017, 03:16:49 AM
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