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: Understanding the Concept:
One formula unit of \(\text{Al}_2(\text{SO}_4)_3\) holds 2 aluminium atoms and 3 sulfur atoms. So the mole ratio of Al to S in the compound is always 2 : 3.

Step 2: Key Formula or Approach:
Moles = mass / molar mass. Convert the 4 g of sulfur to moles, scale by 2/3 to get moles of Al, then convert back to grams.

Step 3: Detailed Explanation:
Moles of S = \(\dfrac{4}{32} = 0.125\) mol.
Moles of Al = \(0.125 \times \dfrac{2}{3} = 0.0833\) mol.
Mass of Al = \(0.0833 \times 27 = 2.25\) g.
Option (B) 2.50 g, (C) 2.0 g and (D) 2.75 g do not match this ratio. They come from using a wrong ratio such as 1 : 1 or from rounding errors.

Final Answer:
The compound holds 2.25 g of aluminium. \[ \boxed{\text{(A) }2.25\ \text{g}} \]