Which of the following represents the correct number of moles of each element in 40 g of Ferric sulphate [Atomic mass Fe = 56 u, S = 32 u, O = 16 u]

Question

Accepted Answer

To determine the correct number of moles of each element in 40 g of ferric sulfate (Fe₂(SO₄)₃), we first need to calculate the molar mass of ferric sulfate and then find the moles of each element based on the given mass.

1. **Calculate the molar mass of Fe₂(SO₄)₃:**

- Ferric sulfate consists of 2 iron (Fe) atoms, 3 sulfur (S) atoms, and 12 oxygen (O) atoms.
   - The atomic masses are: Fe = 56 u, S = 32 u, O = 16 u.

$$
   \text{Molar mass of Fe}_2(\text{SO}_4)_3 = (2 \times 56) + (3 \times 32) + (12 \times 16)
   $$

$$
   = 112 + 96 + 192 = 400 \, \text{g/mol}
   $$

2. **Calculate the number of moles of Fe₂(SO₄)₃ in 40 g:**

$$
   \text{Moles of Fe}_2(\text{SO}_4)_3 = \frac{40 \, \text{g}}{400 \, \text{g/mol}} = 0.1 \, \text{mol}
   $$

3. **Determine the moles of each element:**

- **Iron (Fe):** There are 2 moles of Fe in 1 mole of Fe₂(SO₄)₃.
     $$
     \text{Moles of Fe} = 0.1 \, \text{mol} \times 2 = 0.2 \, \text{mol}
     $$

- **Sulfur (S):** There are 3 moles of S in 1 mole of Fe₂(SO₄)₃.
     $$
     \text{Moles of S} = 0.1 \, \text{mol} \times 3 = 0.3 \, \text{mol}
     $$

- **Oxygen (O):** There are 12 moles of O in 1 mole of Fe₂(SO₄)₃.
     $$
     \text{Moles of O} = 0.1 \, \text{mol} \times 12 = 1.2 \, \text{mol}
     $$

Thus, the correct number of moles of each element in 40 g of ferric sulfate is Fe-0.2, S-0.3, O-1.2, which corresponds to Option 3.

**Explanation of why other options are incorrect:**

- **Option 1 (Fe-2; S-3; O-12):** This option incorrectly suggests that there are whole moles of each element, which would only be true if we had 400 g of ferric sulfate, not 40 g.

- **Option 2 (Fe-1; S-1; O-4):** This option does not reflect the stoichiometry of Fe₂(SO₄)₃ and incorrectly calculates the moles of each element.

- **Option 4 (Fe-0.1; S-0.1; O-0.4):** This option underestimates the moles of each element, not accounting for the correct stoichiometric ratios in Fe₂(SO₄)₃.

Therefore, Option 3 is the correct answer, as it accurately represents the moles of each element in 40 g of ferric sulfate.