Question

27 gm aluminium will react completely with:

• A. $32gm$ oxygen
• B. $24gm$ oxygen
• C. $16gm$ oxygen
• D. $8gm$ oxygen

Answer 1

Answer: (B)

$24gm$ oxygen

The balanced equation for the reaction between aluminium ($Al$) and oxygen ($O_2$) to form aluminium oxide ($A{l}_2{O}_3$) can be written as:
$4Al+3O_2\to 2A{l}_2{O}_3$
Applying the law of conservation of mass:
$4$ moles of $Al$ react with $=$ $3$ moles of $O_2$
$1$ mole of $Al$ $\left(27gm\right)$ react with $=$ $\frac{3}{4}$ moles of $O_2$
$\therefore$ Mass of reacting oxygen $=\frac{3\times 32}{4}=24gm$