After burning 6.08g of silicon and carbon mixture, 8.4g of solid product was produced. The gaseous product was let through a 100mL 15% NaOH solution (density = 1.1g/cm^3). What was the silicon and carbon composition in grams?

1 Answer
Aug 26, 2016

The reaction of excess oxygen with C
C(s)+O_2(g)->=CO_2(g)....(1)

The reaction of excess oxygen with Si
Si(s)+O_2(g)->=SiO_2(s)...(2)

The solid burning product of the mixture is SiO_2

The atomic masses are

Si->28g/(mol)

O->16g/(mol)

Molar mass of

SiO_2->(28+2*16)g/(mol)=60g/(mol)

From equation(2) we see

60g SiO_2(s) is obtained from 28g Si(s)

So 8.4gSiO_2(s) is obtained from (28xx8.4)/60g Si(s)
=3.92g

So composition in the mixture

color(red)(Si->3.92g" "C->(6.08-3.92)g=2.16g")