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?

Aug 26, 2016

The reaction of excess oxygen with C
$C \left(s\right) + {O}_{2} \left(g\right) \to = C {O}_{2} \left(g\right) \ldots . \left(1\right)$

The reaction of excess oxygen with Si
$S i \left(s\right) + {O}_{2} \left(g\right) \to = S i {O}_{2} \left(s\right) \ldots \left(2\right)$

The solid burning product of the mixture is $S i {O}_{2}$

The atomic masses are

$S i \to 28 \frac{g}{m o l}$

$O \to 16 \frac{g}{m o l}$

Molar mass of

$S i {O}_{2} \to \left(28 + 2 \cdot 16\right) \frac{g}{m o l} = 60 \frac{g}{m o l}$

From equation(2) we see

60g $S i {O}_{2}$(s) is obtained from 28g Si(s)

So 8.4g$S i {O}_{2}$(s) is obtained from $\frac{28 \times 8.4}{60} g S i \left(s\right)$
$= 3.92 g$

So composition in the mixture

$\textcolor{red}{S i \to 3.92 g \text{ "C->(6.08-3.92)g=2.16g}}$