Question

un hidrocarburo saturado gaseoso esta formado por un 80% de carbono. ¿Cual es su formula molecular si en condiciones normales si densidad es 1,34 g*L-1

Answer 1

1. Calcular % de H

% H = 100% - 80% = 20 % de H

2. Calcular moles de cada elemento

C: 80 g / 12 g/mol = 6.67 mol
H: 20 g/1 g/mol = 20 mol

3. dividir entre el menor de los resultados:

C: 6.67 mol / 6.67 mol = 1
H: 20 mol / 6.67 mol = 3

4. Fórmula empírica:  CH3

5. Calcular Mm FE

C: 1 x 12 = 12 g/mol
H:  3 x 1 = 3 g/mol
```````````````````````````````
       Mm = 15 g/mol

6. aplicar la ley general de los Gases ya que la fórmula molecular CN

V · P = n · R · T

T= 273 K
P =  1 atm
R = 0.0821 (L atm/mol K)

n = m/Mm (1)   ;  d = m/v (2)

sustituir (1)  V · P = m/Mm · R · T  despejar Mm y V

P · Mm = m/ v · R · T    sustituir m/v = d

Mm = d · R · T
         `````````````
               P
Calcular Mm del gas

Mm = 1.34 g/mL · 0.0821 ( L · atm / mol · K) · 273 K
         ``````````````````````````````````````````````````````````````
                                       1 atm

Mm = 30.03 g/mol

7. Calcular n = Mm compuesto/Mm FE

n = 30 g/mol / 15 g/mol

n = 2

8. Formula molecula: (CH3)2 = C2H3   /   ( CH3 - CH3 )  etano