Molar equivalent mass isn't a standard term in chemistry. The concept you're likely looking for is equivalent weight or gram equivalent weight, which is closely related to molar mass. The molar mass is the mass of one mole of a substance, while the equivalent weight depends on the substance's reactivity in a specific chemical reaction.
Understanding Equivalent Weight
Equivalent weight (EW) represents the mass of a substance that will react with or displace one mole of hydrogen ions (H⁺) or one mole of electrons in a chemical reaction. It's calculated by dividing the molar mass (M) by the number of equivalents (n). The number of equivalents depends on the substance's chemical behavior:
- For acids: n is the number of acidic hydrogens (H⁺) that can be donated per molecule. For example, HCl has n=1, H₂SO₄ has n=2 (in many reactions).
- For bases: n is the number of hydroxide ions (OH⁻) that can be accepted per molecule. For example, NaOH has n=1, Ca(OH)₂ has n=2.
- For salts and other ionic compounds: n is determined by the charge of the cation or anion involved in the reaction. For example, in the reaction involving NaCl, n would be 1 for both Na⁺ and Cl⁻.
- In redox reactions: n is the number of electrons gained or lost per molecule.
Formula: Equivalent Weight (EW) = Molar Mass (M) / n
Example:
Sulfuric acid (H₂SO₄) has a molar mass of approximately 98 g/mol. In many reactions, it donates two protons (H⁺), so n = 2. Therefore, its equivalent weight is 98 g/mol / 2 = 49 g/eq.
Milliequivalent
A milliequivalent (mEq) is one-thousandth of an equivalent weight (1/1000 of a gram equivalent weight). It's frequently used in clinical settings and analytical chemistry for expressing the concentration of electrolytes in solutions.
Key Differences from Molar Mass
- Molar mass is a constant property of a substance, representing the mass of one mole of its molecules or formula units.
- Equivalent weight is context-dependent; it varies depending on the specific reaction the substance is involved in.
Based on the provided references, the concept of "molar equivalent mass" isn't explicitly defined. The term equivalent weight is the relevant concept when considering the mass of a substance relative to its reaction capacity.
