Question

In urma descompunerii termice a 4,38 g de substanta organica cu masa molara 146g/mol se obtin 2,016 dm^3 CO, 3,36 dm^3 CO2 si 4,86g H2O .Determina formula moleculara a substantei.

Answer 1

Calculam masa de C, respectiv masa de H din gazele rezultate
1mol CO........22,4l..........12g C
....................2,016l........1,08g C
1mol CO2.....22,4l...........12g C
......................3,36l..........1,8g C
mC=2,88g
1mol H2O.......18g..........2g H
.....................4,86g.....0,54g H
mH=0,54g
mO=4,38-2,88-0,54=0,96g
impartim masele elementelor la masele atomice, obtinand numarul de moli, apoi la numarul cel mai mic, de unde obtinem formula bruta
................................|÷0,06
C: 2,88/12=0,24........4
H: 0,54/2=0,54..........9
O: 0,96/16=0,06........1
(C4H9O)n - f.bruta
Mbruta=(4*12+9+16)n=73n=126 => n=2
f.m: C8H18O2