Question

The molar mass of Al is 27.0 g/mol.
The molar mass of S is 32.1 g/mol.
The molar mass of O is 16.0 g/mol.
Calculate the molar mass for the compound Al2 (SO4)3 .

Answer 1

To calculate the molar mass of the compound \( \text{Al}_2(\text{SO}_4)_3 \), we need to determine the contribution of each element in the compound based on its chemical formula.

1. **Aluminum (Al)**: There are 2 aluminum atoms.
\[
\text{Molar mass of Al} = 27.0 \, \text{g/mol}
\]
Total mass from Al:
\[
2 \times 27.0 \, \text{g/mol} = 54.0 \, \text{g/mol}
\]

2. **Sulfur (S)**: There are 3 sulfate ions (\( \text{SO}_4^{2-} \)), and each sulfate contains 1 sulfur atom. Therefore, there are:
\[
3 \times 1 = 3 \text{ sulfur atoms}
\]
The molar mass of S:
\[
\text{Molar mass of S} = 32.1 \, \text{g/mol}
\]
Total mass from S:
\[
3 \times 32.1 \, \text{g/mol} = 96.3 \, \text{g/mol}
\]

3. **Oxygen (O)**: Each sulfate ion has 4 oxygen atoms, and with 3 sulfate ions, the number of oxygen atoms is:
\[
3 \times 4 = 12 \, \text{oxygen atoms}
\]
The molar mass of O:
\[
\text{Molar mass of O} = 16.0 \, \text{g/mol}
\]
Total mass from O:
\[
12 \times 16.0 \, \text{g/mol} = 192.0 \, \text{g/mol}
\]

Now, we add all these contributions together to find the total molar mass of \( \text{Al}_2(\text{SO}_4)_3 \):

\[
\text{Total molar mass} = \text{mass from Al} + \text{mass from S} + \text{mass from O}
\]
\[
\text{Total molar mass} = 54.0 \, \text{g/mol} + 96.3 \, \text{g/mol} + 192.0 \, \text{g/mol}
\]
\[
\text{Total molar mass} = 342.3 \, \text{g/mol}
\]

Thus, the molar mass of \( \text{Al}_2(\text{SO}_4)_3 \) is **342.3 g/mol**.