need some chem help!!!!?

Question

a mixture of cyclopropane gas and oxygen is used as an anesthetic. Cyclopropane contains 85.7% C and 14.3 % H by mass. At 50 degrees celcius and .984 atm pressure, 1.56 g cyclopropane has a volume of 1.00 L. What is the molecular formula of cyclopropane?

Answer 1

1. Use ideal gas equation PV = nRT - solve for n (number of moles)

P = .984 atm
V = 1.0 L
T = (50 + 273) = 323 K
R = .08206 L * atm / (L * k)

You get n = .037 moles
Since you have 1.56g
Molar mass must be 1.56/.037 = 42.16 g/mol
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Make an empirical formula by diving the %'s by molar mass of C and H
85.7/12 = 7
14.3/1 = 14
So, 7:14
So you have C7H14, reduce (CH2)n

You have the molar mass of cyclopropanefrom above being 42
and 42/ (molar mass of ch2, 14) = 3 = n

(CH2)3 = C3H6!

Answer 2

First solve the empirical formula.

Divide each of the percentages by the respective mol. mass to get the mole ratios. Convert to whole numbers and you have the E.F.

Now use the ideal gas law PV=nRT

You have T (must be in Kelvin), P and V. R will be 0.082

Solve for n = moles. You have the mass, so you can solve for molecular mass.

Compare that to the E.F. and you have the molecular formula

Answer 3

Use the formula CnH2n. Or here's a thought, look it up in a book!