Question

If 1.5 moles of oxygen combines with $Al$ to form $A{l}_2{O}_3,$ the mass of $Al$ in gram (atomic mass of $Al=27$ ) used in the reaction is :

• A. $2.7$
• B. $54$
• C. $40.5$
• D. $81$

Answer 1

Answer: (B)

$54$

$\underset{4moles}{4Al}+\underset{3moles}{3O_2}⟶\underset{2moles}{2A{l}_2{O}_3}$

3 moles of $O_2$ combine with 4 moles of $Al$

$\therefore 1.5$ moles of $O_2$ will combine with $x$ mol of $Al$

$x=\frac{4}{3}\times 1.5=2$ mol

Thus mass of $Al$ used in the reaction$=2\times 27g=54g$

Hence, option B is correct.