Question

An analysis of Pyrex glass showed the presence of 12.9% of $B_2{O}_3$, 2.2% of $A{l}_2{O}_3$, 3.8% of $N{a}_{2}O$, 0.4% of $K_{2}O$ and the remaining was $Si{O}_2$. What is the ratio of silicon to boron atoms in the glass?

• A. $1:7.3$
• B. $3.65:1$
• C. $1:4.3$
• D. $4.3:1$

Answer 1

The correct option is B $3.65:1$

Let us assume 100 g pyrex glass
Percentage of $B_2{O}_3=12.9\%$
Mass of $B_2{O}_3=12.9g$
Percentage of $Si{O}_2=100-[12.9+2.2+3.8+0.4]=80.7\%$
Mass of $Si{O}_2=80.7g$
Number of moles of $B_2{O}_3=\frac{\text{Mass}}{\text{Molar mass}}=\frac{12.9}{70}=0.184$
Number of moles of boron atoms $=2\times 0.184$
Number of moles of $Si{O}_2=\frac{\text{Mass}}{\text{Molar mass}}=\frac{80.7}{60}=1.345$
Number of moles of silicon atoms $=1.345$
$\frac{\text{Number of atoms of silicon}}{\text{Number of atoms of boron}}=\frac{N_A\times 1.345}{N_A\times 0.184\times 2}=\frac{3.65}{1}$
Where, $N_A$ = Avogadro′s number