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science(chem)

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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

  • science(chem) -

    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?

  • science(chem) -

    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.

  • science(chem) -

    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

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