Mass fraction problem!

1. Dec 2, 2008

lucky_star

1. The problem statement, all variables and given/known data
If 100 g H2O contains 11.2 g H, what mass of water could be obtained from 3.06 g H2(g) reacting with an excess of O2(g)?

2. Relevant equations
Mass % of X in a sample= (Mass of X in sample/ Mass of the sample)*100

3. The attempt at a solution
The parts that confused me were 11.2g of H and the 3.06g H2. Why aren't both be H2 or H? Can anyone help me with this problem? THank you in advance.

This is my effort:
I look for the mass fraction of H in 100g of H2O:
11.2g of H/100g H2O= .112

Then, I find the Mass of H2O
3.06g/.112 = 27.3g H2O

Is this correct?

2. Dec 3, 2008

Staff: Mentor

Is mass of 3.5 g of H different from the mass of 3.5 g H2? Do they differ in number of atoms of hydrogen?

Yes.

3. Dec 3, 2008

lucky_star

No, they are not the same. I understand it now.

Thank you Borek!

4. Dec 4, 2008

Staff: Mentor

Oops, not good. They ARE the same and they DON'T differ in terms of the number of hydrogen atoms.

5. Dec 4, 2008

lucky_star

Oh, Thanks again :)