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?

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Answer 1 · 2016-08-26T06:49:06

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 8.4g#SiO_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")#