Question

Silicon and hydrogen form a series of compounds with the general formula $S{i}_x{H}_y$ . A $6.22g$ sample of the compound is burnt in oxygen. All the $Si$ is converted to $11.64g$ of $Si{O}_2$ and all of the hydrogen is converted to $6.980g$ of $H_{2}O$ .What is the value of ${\displaystyle \frac{y}{x}}$ ?
( $Si=28$ )

Answer 1

Hint: Binary silicon-hydrogen compounds are saturated chemical compounds with the empirical formula $S{i}_x{H}_y$ . All contain tetrahedral silicon and terminal hydrides. They only have $Si-H$ and $Si-Si$ single bonds. The bond lengths are $146pm$ for a $Si-H$ bond and $233pm$ for a $Si-Si$ bond.

Complete Step by Step solution
According to the question, a compound that is a silicon-hydrogen compound is burnt in the presence of oxygen that means combustion will take place. So, the reaction can be given as:
Combustion of compound $S{i}_x{H}_y$ ,
\;S{i_x}{H_y} + {O_2} \to xSi{O_2} + \dfrac{y}{2}{H_2}O
As we know that the atomic mass of silicon is $28$ , oxygen is $16$ and hydrogen is $1$ .
So, $1mole$ of $S{i}_x{H}_y$ weighs: $28x+y$
And $xmole$ of $Si{O}_2$ weighs: $x(28+16\times 2)\Rightarrow 60xg$
Similarly, ${\displaystyle \frac{y}{2}}mole$ of $H_{2}O$ weighs: ${\displaystyle \frac{y}{2}}(2\times 1+16)\Rightarrow 9yg$
As the question states that $11.64g$ of $Si{O}_2$ is formed and $6.980g$ of $H_{2}O$ is formed on combustion.
So mathematically we can write:
 $$\begin{gathered} {\displaystyle \frac{60x}{9y}}={\displaystyle \frac{11.64}{6.980}} \\ \Rightarrow {\displaystyle \frac{x}{y}}={\displaystyle \frac{1}{4}} \end{gathered}$$
Hence, ${\displaystyle \frac{y}{x}}={\displaystyle \frac{4}{1}}$ .

Additional Information
Elemental silicon is added to molten cast iron. It improves the performance in casting thin sections. It also prevents the formation of cementite. It acts as a sink for oxygen when used in molten iron. Due to which the steel carbon content can be more closely controlled because they are kept within narrow limits for each type of steel.

Note
Silane is explosive when treated with air $(1-98\mathrm{\%}Si{H}_4)$ . Other lower silanes also have the ability to form explosive mixtures with air. The lighter the liquid silanes the highly flammable they are, but this risk decreases with increase in the length of silicon chain. Heptasilane don't react spontaneously and they can be stored in the form of gasoline. Higher silanes have the ability to replace hydrocarbons as storable energy sources with the advantage to react with both oxygen and nitrogen.