Notez: "*" inmultire si "/" impartire:
a=22g CO2
b=9g H2O
s.o=7g
Pentru a calcula %C si %H folosim 2 formule si anume: %C=300a/11s si %H=100b/9s
%C=300a/11s=300*22/11*7=6600/77=85.71
%H=100b/9s=100*9/9*7=900/63=14.28
Aflu formula bruta:
nC=%C/AC=85.71/12=7.142
nH=%H/AH=14.28/1=14.28
===>(CH2)n
Masa moleculara a compusilior cu formula moleculara (CH2)n este: M=(12+2)n=14n
M=28g/mol
14n=28 ===>n=2. Formula moleculara C2H4
Metodă mai usoară..
Avem Mhidrocarbura=28g/mol si mhidrocarbuura=7g, a=22g CO2, b=9g H2O
Aflăm nr moli de hidrocarbura si nr moli de C si H:
n=m/M=7/28=0.25moli
n=m/M=22/44=0.5moli C
n=m/M=9/18=0.5=1 mol H2
0.25moli......0.5moli.......1mol
1 mol.............2 atomi C ....4 atomi H2
