Question

Calculate the amount of aluminium present in \(\text{Al}_2(\text{SO}_4)_3\) if the compound contains 4 g of sulfur.
[Molar mass of sulfur = 32 g/mol , Molar mass of Al =27 g/mol ]

• A. \(2.25\) g
• B. \(2.50\) g
• C. \(2.0\) g
• D. \(2.75\) g

Hint:

Find moles of sulfur, then use the 2 Al : 3 S ratio in the formula.

Answer 1

The Correct Option is A

Step 1: Mass ratio method:
In one formula unit, aluminium has mass $2 \times 27 = 54$ u and sulfur has mass $3 \times 32 = 96$ u.

Step 2: Proportion:
The mass ratio Al : S is fixed at 54 : 96 in every sample of the compound.
So $\dfrac{m_{Al}}{4} = \dfrac{54}{96}$.

Step 3: Solve:
$m_{Al} = 4 \times \dfrac{54}{96} = 4 \times 0.5625 = 2.25$ g.
The other values (2.50, 2.0, 2.75 g) would need a different Al : S mass ratio, which this compound does not have.

Final Answer:
Aluminium present is 2.25 g. \[ \boxed{\text{(A) }2.25\ \text{g}} \]