JEE MAIN - Chemistry (2025 - 23rd January Evening Shift - No. 23)
When 81.0 g of aluminium is allowed to react with 128.0 g of oxygen gas, the mass of aluminium oxide produced in grams is ________ . (Nearest integer)
Given :
Molar mass of Al is $27.0 \mathrm{~g} \mathrm{~mol}^{-1}$
Molar mass of O is $16.0 \mathrm{~g} \mathrm{~mol}^{-1}$
Answer
153
Explanation
$4 \mathrm{Al}+3 \mathrm{O}_2 \longrightarrow 2 \mathrm{Al}_2 \mathrm{O}_3$
$$\begin{aligned} & \frac{81}{27}=3 \text { mole } \frac{128}{32}=4 \text { mole } \\ & \text { Limiting reagent } \\ & \therefore \text { mole of } \mathrm{Al}_2 \mathrm{O}_3 \text { formed }=\frac{1}{2} \times 3 \text { mole } \\ & \therefore \text { wt. of } \mathrm{Al}_2 \mathrm{O}_3 \text { formed }=\frac{3}{2} \times 102 \\ & =153 \mathrm{gm} \end{aligned}$$
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