What is the equivalent mass of MgSO4 (magnesium sulfate)? Formula: MM/f where: MM = molar mass and f = chemical factor
The Correct Answer and Explanation is:
Correct Answer:
The equivalent mass of magnesium sulfate (MgSO₄) is 120.37 g/equiv.
Explanation:
To find the equivalent mass of a compound, use the formula:
Equivalent Mass = Molar Mass (MM) ÷ Chemical Factor (f)
Step 1: Determine the Molar Mass of MgSO₄
Break it down using atomic masses:
- Magnesium (Mg) = 24.31 g/mol
- Sulfur (S) = 32.07 g/mol
- Oxygen (O) = 16.00 g/mol × 4 = 64.00 g/mol
So,
Molar Mass (MM) = 24.31 + 32.07 + 64.00 = 120.38 g/mol
For simplicity, we can use 120.37 g/mol, which is the commonly accepted rounded value.
Step 2: Identify the Chemical Factor (f)
The chemical factor (f) depends on the reaction type. In acid-base reactions, it relates to how many H⁺ or OH⁻ ions a substance can donate or accept. In redox or salt reactions, it refers to the number of electrons transferred or charges balanced.
For MgSO₄, it is a neutral salt that typically forms from Mg²⁺ and SO₄²⁻. In reactions where MgSO₄ dissociates fully into one Mg²⁺ ion and one SO₄²⁻ ion, the chemical factor is 1, because 1 mole of MgSO₄ provides 2 equivalents of charge (1 Mg²⁺).
However, since Mg²⁺ is the reacting ion in most stoichiometric uses of MgSO₄ (e.g., precipitation, neutralization), and it provides 2 positive charges, the chemical factor (f) is 2.
Step 3: Calculate the Equivalent Mass
Equivalent Mass = 120.37 ÷ 2 = 60.19 g/equiv
So depending on the context:
- If MgSO₄ acts as a source of Mg²⁺, use f = 2 → Equivalent Mass = 60.19 g/equiv
- If the full salt is reacting as one unit (rare), use f = 1 → Equivalent Mass = 120.37 g/equiv
But the most accepted chemical factor for MgSO₄ is 2, hence the equivalent mass is 60.19 g/equiv.
