Question

A gaseous hydrogen and carbon containing compound is decomposed and found to contain 82.66% carbon and 17.34% hydrogen by mass. The mass of 158 mL of the gas, measured at 556 mmHg and 25 ∘C, was found to be 0.275 g. What is the molecular formula of the compound?

Answer 1

use the ideal gas law and rearrange it for molecular mass, M.

PV=nRT -> PV=mRT/M -> M=mRT/PV

plug in your values, find M

find the mass that contributes to each of the elements (multiply M by their %) and find how many of atoms of each are present in the formula.

Answer 2

I'm still lost.

Answer 3

ok i tried the ideal gas law for M of carbon, and i got a really high number (1440). not sure if i'm doing it right

Answer 4

I think you tried it as i did because i got the same number but it said it was incorrect. Thank you :)

Answer 5

the answer is
Carbon- 1
Hydrogen-2
Fluorine- 2

Answer 6

@kishnktty:

Let UNITs guide you; always USE THEM in your calculation to prevent errors

moles = PV/RT = (556 mm/760mm/atm)*0.158liter / (0.08205liter-atm/moleK * 298K) = ??

MW = 0.275 g / ?? moles = ??

Empirical formula = C(82.66/12.01)H(17.34/1.008) ---- C1H2.5

MW/Empirical W ==> Molecular Formula/Empirical Formula

Answer 7

ok i got most of what you're saying, @save. but how can i find the molecular formula using the MW,Emp W, and Emp formula?

Answer 8

\(M=\dfrac{(0.275 g)*(0.08206)*(25+273)}{(\dfrac{556}{760} atm)*(0.158 L)}=58.1784 ~g/mol\)

C = 82.66%*58.1784 g/mol=48.1 g/mol/12 g/mol= 4 Carbon atoms
H=17.34%*58.1784 g/mol= 10.1 g/mol/1 /mol = 10 Hydrogen atoms

\(C_4H_{10}\) which is butane

Answer 9

y'all did it wrong