What is the molecular formula of this compound ?

Question

Elemental ananalysis of a compound results in the following data

40.00 % C

6.71 % H

53.28 % O



3.60 g of the compound fills a 190.0 ml bottle with a pressure of 3871.1 mm Hg at a temperature of 21.7oC. What is the molecular formula of this compound ?

Answer 1

Formaldehyde, H2CO

Answer 2

40.00 % C ==> 40/12.011 = 3.33 C
6.71 % H ==> 6.71/1.0079 = 6.66 H
53.28 % O ==> 53.28/15.9994 = 3.33 O

gives CH2O as the empirical formula

using the PV data

V = 0.190 L
P = 3871.1mmHg
T = 21.7ºC + 273.15 = 294.85 K
R = 62.364 L • mmHg/ K • mole
n = ?

n = PV/RT = (3871.1 mmHg) (0.190L) / (62.364 L • mmHg/ K • mole) (294.85 K) =

= 0.04 moles

MW = g/moles = 3.6 g/0.04 moles = 90 g/mole

which corresponds to C3H6O3 = 90.078 g/mole from atomic weights