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 183.0 ml bottle with a pressure of 4042.4 mm Hg at a temperature of 23.4oC. What is the molecular formula of this compound ?

Answer 1

we have PV = m/M * R * T
T = t(celsius) + 273
R = 0.082 = const
M is the molecular mass
P is the pressure (1atm = 760 mmHg)

so M = (m*R*T)/(P*V) = 3.6 * 0.082 * (23.4+273)/(4042.4/760 * 0.183 )= 90 g/mol

with the percentages we can find the compound

the formula is CxHyOz (x,y,z is the number of atoms)

x : y : z = %C/M(C) : %H/M(H) : %O/M(O) = 40/12 : 6.71/1 : 53.28/16 = 3.33 : 6.71 : 3.33 = x : 2x : x

we can use this table to find the answer
x=1 ; M = 30 : CH2O
x=2 ; M = 60 : C2H4O2
x=3 ; M = 90 : C3H6O3
so the formula is C3H6O3