Question

O subst. organica are densitatea fata de aer egala cu 2,49. Prin arderea completa a 144g substanta cu 1232 L aer (cu 20% oxigen ) rezulta 144 g apa . Care este Formula moleculara a apei ?

Answer 1

daer=Msubst/Maer => Msubst=daer*Maer=2,49*28,9=72g/mol
transformam masele si volumul de aer in moli, pentru calcule mai usoare pe reactie
intai, Vaer=5VO2 => VO2=246,4l
nsubst=m/M=144/72=2moli
nO2=V/Vm=246,4/22,4=11moli
nH2O=m/M=144/18=8moli
notam formula moleculara: CxHyOz
2moli............(4x+y-2z)/2 moli..y moli
2CxHyOz + (4x+y-2z)/2 O2 -> yH2O + 2xCO2
2moli..............11 moli.............8moli
y=8 si (4x+y-2z)/2=11
4x+y-2z=22 => 2(2x-z)=22-8=14=> 2x-z=7 => z=2x-7 (I)
MCxH8Oz=12x+8+16z=12x+8+16(2x-7)=12x+8+32x-112=72
44x=176 => x=4
z=2*4-7=1
f.m: C4H8O