science(chem)
posted by ~christina~ on .
I did a dehydration rxn with 1.424g of 4methylcyclohexanol with .40ml 85% H3PO4 and 6 drops of concentrated H2SO4.
I have to calculate the limiting reagent even though I do suspect it to be the 4methylcyclohexanol.
I do know the ratio is 1mol H3PO4: 3mol 4methylcyclohexanol.
However even though I have the weight of my 4methylcyclohexanol I have the ml of my H3PO4 I added.
.40ml 85% H3PO4
I was wondering how do I calculate how many moles I have of it. Can I just use the density to convert it or not?
I was wondering that since it isn't full strength but 85% H3PO4. Would that affect the calculations?
Thank You

I think I got it.
I looked it up online and found that concentrated H3PO4 is 85% and it is 15M so I'd have (.40ml)
which would = .006mol H3PO4 that I have.
Is this right? 
Close enough.
specific gravity 85% H3PO4 is 1.69.
Density = 1.69 g/mL.
mols H3PO4 = 1.69 g/mL x 0.4 mL x (85 g/100 g) x (1 mol/98 g) = 0.00586.
As you suspect, I would be VERY surprised if H3PO4 is the limiting reagent. 
Oh yep. I went on Wiki to verify the density from that site I looked up and I saw it was 1.69 which was close to 1.7 so I figured it was fine.
Thanks Dr.Bob