The percentage composition of elements in a compound is calculated from the molecular formula of the compound. The molecular mass of a compound is calculated from the atomic masses of the various elements present in the compound. The percentage of mass of each element is then calculated with the help of the following relation. Percentage mass of the element in the compound.
`("Mass of the element")/("Mass of the compound")`
Percentage of S in aluminium sulphate is

Options

A. 28
B. 56
C. 65
D. 75

Explanation

To calculate the percentage of sulfur (S) in aluminum sulfate (Al₂(SO₄)₃), we will follow these steps:

### Step 1: Determine the Molecular Formula
The molecular formula of aluminum sulfate is Al₂(SO₄)₃.

### Step 2: Calculate the Molar Mass of the Compound
To find the molar mass of aluminum sulfate, we need to sum up the atomic masses of all the elements in the formula:

- **Aluminum (Al)**: The atomic mass of aluminum is approximately 27 g/mol. Since there are 2 aluminum atoms:
\[ \text{Mass of Al} = 2 \times 27 = 54 \text{ g/mol} \]

- **Sulfur (S)**: The atomic mass of sulfur is approximately 32 g/mol. Since there are 3 sulfur atoms:
\[ \text{Mass of S} = 3 \times 32 = 96 \text{ g/mol} \]

- **Oxygen (O)**: The atomic mass of oxygen is approximately 16 g/mol. Since there are 12 oxygen atoms (4 from each sulfate group and there are 3 sulfate groups):
\[ \text{Mass of O} = 12 \times 16 = 192 \text{ g/mol} \]

Now, we can calculate the total molar mass of aluminum sulfate:
\[ \text{Molar Mass of Al₂(SO₄)₃} = \text{Mass of Al} + \text{Mass of S} + \text{Mass of O} \]
\[ = 54 + 96 + 192 = 342 \text{ g/mol} \]

### Step 3: Calculate the Percentage of Sulfur
Now, we can calculate the percentage of sulfur in aluminum sulfate using the formula:
\[ \text{Percentage of S} = \left( \frac{\text{Mass of S}}{\text{Mass of compound}} \right) \times 100 \]
Substituting the values:
\[ \text{Percentage of S} = \left( \frac{96}{342} \right) \times 100 \]
Calculating this gives:
\[ \text{Percentage of S} \approx 28.07\% \]

### Final Answer
The percentage of sulfur in aluminum sulfate is approximately **28%**.

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