Question

The atomic weight of silicon is $28.086$ and that of oxygen is $15.9994$ (on the $C^{12}$ scale). Calculate the mass in grams of a single molecule of $Si{O}_2$.

• A. $9.977\times {10}^{-23}gm$
• B. $9.8\times {10}^{-22}gm$
• C. $1\times {10}^{-22}gm$
• D. $6.6\times {10}^{-23}gm$

Answer 1

Answer: (A)

$9.977\times {10}^{-23}gm$

Molecular weight of $Si{O}_2$ is $28.086+2\times 15.9994=60.08$ u

$\therefore$ 1 mole of $Si{O}_2$ weighs 60.08 g

$\Rightarrow$ $6.022\times {10}^{23}$ moelcules weigh 60.08 g of $Si{O}_2$ (By Avogadro's Rule)

1 molecule of $Si{O}_2$ contains $\frac{60.08g}{6.022\times {10}^{23}}\times 1=9.977\times {10}^{-23}g$

$\therefore$ Mass of a single molecule of $Si{O}_2=9.977\times {10}^{-23}g.$