I did a dehydration rxn with 1.424g of 4-methylcyclohexanol 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 4-methylcyclohexanol.
I do know the ratio is 1mol H3PO4: 3mol 4-methylcyclohexanol.
However even though I have the weight of my 4-methylcyclohexanol 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
To calculate the number of moles of H3PO4 you have, you need to take into account the concentration of the H3PO4 solution, which is given as 85%. Here's how you can calculate it:
1. Find the molar mass of H3PO4: H = 1.01 g/mol, P = 30.97 g/mol, O = 16.00 g/mol (x4).
Molar mass of H3PO4 = (1.01 x 3) + 30.97 + (16.00 x 4) = 98.00 g/mol.
2. Determine the mass of H3PO4 in the solution:
Mass of H3PO4 = 0.40 ml x (density of 85% H3PO4 solution) x (mass of 1 ml of 85% H3PO4 solution).
3. Next, you need to consider that the 85% H3PO4 solution is 85% of the molar mass of pure H3PO4.
Mass of pure H3PO4 = 85% x mass of H3PO4 in the solution.
4. Convert the mass of pure H3PO4 to moles using the molar mass of H3PO4:
Moles of H3PO4 = (mass of pure H3PO4) / (molar mass of H3PO4).
Now that you have the moles of H3PO4, you can compare it to the moles of 4-methylcyclohexanol to determine the limiting reagent. Since you already know the molar ratio between H3PO4 and 4-methylcyclohexanol is 1:3, you can compare the moles.
If the moles of H3PO4 are less than the moles of 4-methylcyclohexanol, then 4-methylcyclohexanol is the limiting reagent. If the moles of H3PO4 are greater than or equal to the moles of 4-methylcyclohexanol, then H3PO4 is the limiting reagent.
Note: The density of the 85% H3PO4 solution and the mass of 1 ml of the solution should be provided in the question or can be obtained from a reference source.