What are the molecular weight and the equivalent weight of h3PO4
The Correct Answer and Explanation is:
Correct Answer:
- Molecular Weight of H₃PO₄ (Phosphoric Acid): 97.99 g/mol
- Equivalent Weight of H₃PO₄: 32.66 g/equiv (for one acidic hydrogen)
Explanation
Phosphoric acid (H₃PO₄) is a triprotic acid, meaning it has three ionizable hydrogen atoms. To understand its molecular and equivalent weights, we need to break down its chemical composition and acidic properties.
1. Molecular Weight:
The molecular weight is the sum of the atomic weights of all atoms in a molecule. For H₃PO₄:
- Hydrogen (H): 1.008 × 3 = 3.024
- Phosphorus (P): 30.97 × 1 = 30.97
- Oxygen (O): 16.00 × 4 = 64.00
Total molecular weight = 3.024 + 30.97 + 64.00 = 97.994 g/mol, often rounded to 97.99 g/mol.
2. Equivalent Weight:
The equivalent weight of an acid is defined as: Equivalent weight=Molecular weightBasicity\text{Equivalent weight} = \frac{\text{Molecular weight}}{\text{Basicity}}
Basicity is the number of replaceable hydrogen ions (H⁺) an acid can donate in a reaction. For H₃PO₄:
- It is triprotic (basicity = 3), so it can donate up to three protons.
- Depending on the reaction or the stage of neutralization, the equivalent weight can change.
- For full neutralization (donating all 3 H⁺): 97.993=32.66 g/equiv\frac{97.99}{3} = 32.66 \text{ g/equiv}
- For donating only one H⁺ (e.g., in reactions with weak bases), the equivalent weight is the same as the molecular weight, i.e., 97.99 g/equiv.
Typically, in titration or stoichiometry problems, the equivalent weight is calculated based on full neutralization unless otherwise specified. Hence, the equivalent weight of H₃PO₄ is 32.66 g/equiv.
Conclusion:
- Molecular weight: 97.99 g/mol
- Equivalent weight (full neutralization): 32.66 g/equiv
Understanding these values is critical in chemistry for calculations involving titration, stoichiometry, and reaction balancing.
