In analytical chemistry and titrations, you rarely use the raw 'Molecular Weight' of a compound. Because different chemicals react with different strengths, chemists use a much more accurate concept called Equivalent Weight.
The universal master formula for calculating Equivalent Weight is: Equivalent Weight = Molecular Weight / n-factor
Master Formula: Eq. Wt = Molecular Wt / n-factor.
n-factor for Acid: Basicity (Number of replaceable H⁺ ions).
n-factor for Base: Acidity (Number of replaceable OH⁻ ions).
n-factor for Salt: Total positive charge on the cation.
Usage: It is absolutely essential for calculating the 'Normality' of a chemical solution in lab titrations.
The only difficult part of calculating the equivalent weight is finding the 'n-factor' (the denominator). The rule for finding the n-factor completely changes depending on whether the chemical is an acid, a base, or a salt.
For acids, the n-factor is its Basicity (the number of H⁺ ions the acid can release in water).
For bases, the n-factor is its Acidity (the number of OH⁻ hydroxide ions the base can release).
For ionic salts, the n-factor is the total positive charge on the metal cation.
The formula is the Molecular Weight of the compound divided by its n-factor (valency factor).
H2SO4 has a molecular weight of 98. Because it has two replaceable hydrogen ions, its n-factor is 2. Dividing 98 by 2 gives an equivalent weight of 49.
For a pure element, the equivalent weight is simply its Atomic Mass divided by its Valency. For example, Oxygen has a mass of 16 and a valency of 2, so its equivalent weight is 8.
Lewis Dot Structure of CO₂ (Carbon Dioxide)
Learn how to draw the Lewis dot structure of CO2. Understand the double bonds, lone pairs on oxygen, and the linear geometry of carbon dioxide.
Lime Water Formula — What Is Lime Water in Chemistry?
Lime water is a dilute aqueous solution of calcium hydroxide Ca(OH)₂. Learn the formula, preparation, and how lime water turns milky with CO₂ — with FAQs.
Which Information is NOT Conveyed by a Balanced Chemical Equation?
Learn which information is not conveyed by a balanced chemical equation. Discover the limitations of chemical equations like rate of reaction and feasibility.
Limitations of Bohr's Atomic Model
Learn the major drawbacks and limitations of Bohr's Atomic Model. Understand why it failed for multi-electron atoms and the Zeeman effect.
Maleic Acid (Formula and Properties)
Learn about Maleic Acid. Understand its chemical formula (C4H4O4), its cis-isomer structure, and its massive industrial uses in making polymers.
Turn this guide into revision flashcards, a practice exam, or an AI-generated podcast — free, no signup required.