Question

Rezolvati problemele:
a)Sa se stabileasca formula moleculara a substantei organice daca la arderea unei probe cu masa 1,5g s-au format 4,4g Co2 si 2,7g H2O.Masa unui litru de aceasta substanta in stare gazoasa constituie 1,34g.

b)La arderea completa a 0,5 mol de hidrocarbura s-au format cite 1,5mol de CO2 si H2O.Densitatea relativa a hodrocarburii in stare gazzoasa in raport cu hidrogenul este egala cu 42.Sa se stabileasca formula moleculara a hidrogenului.

c)In conditii normale 1l de substanta organica gazoasa ce contine carbon,hidrogen si oxigen cintareste 2,05g.La arderea completa a acestei substante s-au format 3,95g Co2 si 2,44g de H2O.Sa se stabileasca formula moleculara a substantei.

Answer 1

a) 1L..............................1,34g
x=1,11940L.....................1,5g

n=V/Vm=1,11940/22,4=0,05 moli s.o

MCO2=AC+ 2AO = 12+2*16=44g/mol

In 44g CO2 se gasesc.................12g C
In 4,4g CO2.................................1,2g C

MH2O=18g/mol

In 18g H2O......................2gH
2,7g H2O........................x=0,3g H

n=m/M=1,2/12= 0,1 moli C

n=m/M=0,3/1= 0,3 moli H

Din 0,05 moli s.o...........0,1 moli C.............0,3 moli H
1mol s.o........................x=2 atomi C.........6 atomi H


Formula moleculara => C2H6 - etanul

b) CxHy

n=m/M=>m=n*M=1,5*44=66g CO2

In 44g CO2.......................12g C
In 66g CO2......................x=18g C

n=m/M=18/12=1,5 moli C

MH2O=18g/mol

n=m/M=>m=n*M=1,5*18=27g H2O

In 18g H2O.............................2gH
27g H2O................................x=3gH

n=m/M=3/1= 3 moli H

dgaz=M/Mgaz=>M=dgaz*Mgaz=42*2=84g/mol

(C1,5H3)n=84 => 12n*1,5+3n=84=>21n=84=>n=4

Formula moleculara => C6H12 -> n-hexanul

c) In 44g CO2........................12g C
3,95g CO2.............................x=1,077272727g C

In 18g H2O.........................2gH
2,44g H2O.........................x=0,27111111g H

mO=2,05-1,077272727-0,27111111=0,701616g O

n=m/M=1,077/12=0,08975 moli C

n=m/M=0,27111/1= 0,027111 moli H

n=m/M=0,70189/16=0,04 moli O

Dupa impartire => C2H6O sau C2H5-OH (alcoolul etilic,etanol)