So we know abosluting nothing about this molecule, other than it has 1 double bond? We don't know if it's a hydrocarbon, or what functional groups it has? I guess pure compound could be telling my something, but I'm not sure what you mean by it >_<
IF this is an alkene, with no other functional groups this problem wouldn't be so bad.
An alkane has the molecular formula C
nH
2n+2Double bonds and rings each take away 2 hydrogens (if you can't visualize this, draw one)
A triple bond will take away 4 hydrogrens.
We have 1 double bond, out molecular formula will be C
nH
2nHydrogenation (H2 should break homolytically, both are pulling on electrons with the same force) will force that pi bond to break (Homolytically I think)..giving us no carbocation, but rather a hydrocarbon, with 2 C having a radical. The 2 H radicals will form up with the 2 C radicals and we get an alkane.
Now here's the kicker. We don't know how many carbons are in this molecule.
Lets start by figuring out how many moles of H2 we have...and I can't remember how the heck to convert mL of gas to grams >_< Okay, I just finished looking it up. I guess you can use the specific gravity of H2 to find the density, and then from there find grams. The specific gravity of H2 is 0.070, evidently multiply this by the density of air at STP will give us the denisty of H2 at STP. 1.2m³ (air) x 0.07=0.084kg/m³. Now I don't know why the used meters cubed as a unit...I have no idea how the heck we're supposed to use a density with meters as a unit when we have mL. If you can figure out how to convert your mL H2 to grams, I may be able to help you with the rest of the problem.
0.150g (unknown) x (1 mole (unknown) / x g (FW unknown) x ( 1 mol H2 / 1 mol unknown) x ( 2.01g H2 / 1 mol H2) = Grams H2 reacted.*
*We know how many mL H2 reacted, if we could figure out how to convert mL H2 to g H2, we'd only have 1 variable in the above work.
* I got the 1 mole Unknown to 1 mole H2 ratio from the simple fact that no matter the size of the hydrocarbon, it can only react with 2 H atoms (1 H2 molecule) per molecule of itself. See:
CH
3-CH
2-CH=CH-CH
2-CH
2-CH
2-CH
3 + H
2 ---> CH
3-CH
2-CH
2-CH
2-CH
2-CH
2-CH
2-CH
3No matter what you change the alkene to, it will only react with 1 molecule H2.
Here is a simplified version of the math above:
(.3015 / x) = z
Where
x is the formula weight of the unknown
z is the grams H2 (which we can solve for, but I don't know how to)
Okay so we know that .150g of this hydrocarbon can take up 25mL of H2 gas. Now this is where is gets tricky. Lets think:
1) If our hydrocarbon contains too many carbons, it will be too heavy and not be able to react with the 25mL H2 with only .150g of itself.
2) If our hydrocarbon contains too few carbons, it will be too light and there will be access of it left after reacting with H2.
So- How can we get a perfect hydrocarbon.
Sorry everything is so messy. I'm really scatterbrained when I'm trying to figure something like this out. I hope I haven't confused you...
Good luck, and please let me know if you figure out how to convert that mL H2 to grams
