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A certain compound containing only carbon and hydrogen was found to have a vapor density of 2.550 g/L at 100 degrees C and 760 mm Hg. If the empirical formula of this compound is CH, what is the molecular formula of this compound?

I had some ideas as to how to solve this problem.

First, I thought of using the Specific Heat Formula to find a value, that could resemble a known element.

Q = m CP delta T
1 = m(2.550)(373.15)
1 = m(951.53)
m = 0.00105 g

At this point, I'm really stuck. I know that to find the molecular formula of a compound, I need to divide the empirical mass over the molecular mass. However, I am not sure how to find both masses. I was thinking to find the empirical mass I could calculate CH.

C = 12.011 g
H = 1.007 g

CH = 12.011 + 1.007 = 13.018 g

  • Chemistry -

    The easiest way to find the molar mass is
    to use a rearranged PV = nRT to
    P*M = density*RT
    M = molar mass
    P in atm.
    T in kelvn.
    Then go through your procedure to change the empirical formula to the molecular formula.

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