What is a gram equivalent?

A gram equivalent is the mass of a substance that reacts with or displaces a fixed amount of another substance. It is calculated as: Gram Equivalents = Mass / Equivalent Weight, where Equivalent Weight = Molecular Weight / n-factor.

n-factor (valence factor) depends on the substance type: for acids it's the number of replaceable H⁺ ions, for bases it's replaceable OH⁻ ions, for salts it's the total positive charge on cations, and for redox reactions it's the total change in oxidation state.

Why don't masses need to be equal in a reaction?

Because different substances have different molecular weights and different n-factors. What must be equal is the number of equivalents — the 'reacting power.' For example, 53g Na₂CO₃ (1 equivalent) reacts with 36.5g HCl (1 equivalent), even though the masses are different.

How is equivalent weight different from molecular weight?

Molecular weight is the mass of one mole of a substance. Equivalent weight is the mass that provides one equivalent of reacting power: Equivalent Weight = Molecular Weight / n-factor. For Na₂CO₃, MW = 106 g/mol but Eq.Wt = 53 g/eq because n-factor = 2.

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Gram Equivalent

PhysicalMediumNEET: 1-2 Q3D

Chemistry lab

Gram Equivalent — Why Masses Don't Match in Reactions

Stoichiometry & Mole Concept

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Equivalents dono taraf barabar karo, phir 'Mix them!' dabao — poora react ho jayega, kuch nahi bachega (masses alag hone ke bawajood)

How to use this lab

1Right pan pe HCl add karke balance ko level karo.
2Na₂CO₃ (n-factor 2) vs HCl (n 1) ka equivalent compare karo.
3Equivalents / Mass tab switch karke dono views dekho.

About this lab

Match the equivalents of Na₂CO₃ (n=2) and HCl (n=1) on a 3D balance, then hit 'Mix them!' and watch both sides react to nothing — even though one pan weighs 53g and the other just 36.5g. Equal equivalents react, unequal mass.

What you're seeing

Jab hum balanced equation dekhte hain (Na₂CO₃ + 2HCl → ...), hum sochte hain ki 1 mole Na₂CO₃ = 2 mole HCl. Lekin equivalents mein dono barabar hote hain — kyunki Na₂CO₃ ka n-factor 2 hai. Equivalent weight = Molecular Weight / n-factor. Jab tak equivalents match nahi hote, reaction complete nahi hota.

Key NEET facts

Equivalent Weight: MW / n-factor
n-factor (Acids): Replaceable H⁺ ions
HCl: n=1 (1 H⁺). H₂SO₄: n=1 ya 2 depending on reaction. H₃PO₃: n=2 (not 3!).
n-factor (Salts): Total cationic charge
Na₂CO₃: 2 Na⁺ = total charge 2, so n=2. CaCl₂: Ca²⁺ = total charge 2, so n=2.
Law of Equivalents: Equivalents of A = Equivalents of B

Memory trick

Equivalent = Mass × n-factor / MW. Yaad rakho: n-factor badhao, equivalent weight ghatao, reacting power badhao.

Practice

Test Yourself

How many grams of HCl are needed to completely react with 53g Na₂CO₃?

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N-Factor Explorer — What Is Reacting Power?

Stoichiometry & Mole Concept

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