Equivalent Weight Calculators

0 calculators tagged with “Equivalent Weight”

Equivalent weight is the mass of a substance that reacts with or provides one mole of reactive units — protons (H⁺), hydroxide ions (OH⁻), or electrons in acid-base or redox reactions. It simplifies stoichiometric calculations when different compounds react in different molar ratios — one equivalent of any acid exactly neutralizes one equivalent of any base, regardless of their molar masses or number of ionizable protons. The concept of equivalent weight underpins the normality (N) concentration system and is widely used in titration, water chemistry, and classical analytical chemistry.

All Calculators

No calculators found for this topic.

What Is Equivalent Weight?

Equivalent weight (Eq. wt.) is calculated differently depending on the reaction type:

Acids

Eq. wt. = Molar mass / Number of ionizable H⁺ ions (n)

  • HCl: n = 1 → Eq. wt. = 36.5/1 = 36.5 g/eq
  • H₂SO₄: n = 2 → Eq. wt. = 98/2 = 49 g/eq
  • H₃PO₄: n = 3 (if all 3 H⁺ are donated) → Eq. wt. = 98/3 = 32.7 g/eq

Bases

Eq. wt. = Molar mass / Number of OH⁻ provided (or H⁺ accepted)

  • NaOH: Eq. wt. = 40/1 = 40 g/eq
  • Ca(OH)₂: Eq. wt. = 74/2 = 37 g/eq

Salts

Eq. wt. = Molar mass / (Valence of cation × number of cations)
Na₂SO₄: cation Na⁺ (valence 1), 2 Na⁺ → Eq. wt. = 142/2 = 71 g/eq

Redox Reactions

Eq. wt. = Molar mass / Number of electrons transferred
KMnO₄ in acidic solution (Mn⁷⁺ → Mn²⁺, 5e⁻ change): Eq. wt. = 158/5 = 31.6 g/eq

Normality (N)

Normality = equivalents of solute per liter of solution:

N = number of equivalents / volume (L) = molarity × n

A 1 M H₂SO₄ solution is 2 N (2 equivalents/L). 1 N H₂SO₄ exactly neutralizes 1 N NaOH — regardless of their molarities.

Application in Titrations

At the equivalence point: N₁V₁ = N₂V₂

This simplification allows acid-base titrations to be calculated without tracking the number of protons per molecule — one equivalent of acid always neutralizes one equivalent of base.

Glossary

Equivalent Weight
The mass of a substance providing one mole of reactive units (H⁺, OH⁻, or electrons). Eq. wt. = Molar mass / n, where n = ionizable H⁺ (acids), OH⁻ (bases), or electrons transferred (redox).
Normality (N)
Concentration expressed as equivalents of solute per liter: N = Molarity × n. Used in titration because N₁V₁ = N₂V₂ at equivalence point — one equivalent of acid always neutralizes one equivalent of base.
Equivalence Point
The point in a titration where the moles of equivalents of titrant exactly equal the moles of equivalents of analyte. At this point N₁V₁ = N₂V₂. Distinguished from the endpoint (where the indicator changes color).

Frequently Asked Questions

Equivalent weight = Molar mass / number of reactive units (n). For acids, n = number of ionizable H⁺ ions. For bases, n = number of OH⁻ ions. For redox compounds, n = number of electrons transferred. Examples: HCl Eq. wt. = 36.5/1 = 36.5 g/eq; H₂SO₄ Eq. wt. = 98/2 = 49 g/eq; NaOH Eq. wt. = 40/1 = 40 g/eq.

Normality (N) = number of equivalents of solute per liter: N = Molarity × n, where n = equivalents per mole. A 1 M H₂SO₄ solution is 2 N because each H₂SO₄ provides 2 H⁺ (2 equivalents/mol). Normality is used in titration calculations because N₁V₁ = N₂V₂ at the equivalence point — one equivalent of acid always reacts with exactly one equivalent of base.

Equivalent weight simplifies titration calculations because all acids and bases react in a 1:1 equivalent ratio at the equivalence point — regardless of how many protons they donate. Rather than tracking that H₂SO₄ donates 2 H⁺ (so a 1 M H₂SO₄ reacts with 2 mol NaOH), normality automatically captures this: 1 N H₂SO₄ exactly neutralizes 1 N NaOH at the equivalence point by N₁V₁ = N₂V₂.

In acidic solution, KMnO₄ is reduced from Mn⁷⁺ to Mn²⁺ — a change of 5 electrons per manganese. Equivalent weight = Molar mass / electrons transferred = 158.03 / 5 = 31.6 g/eq. In neutral solution (MnO₄⁻ → MnO₂, Mn⁷⁺ → Mn⁴⁺, 3 electrons): Eq. wt. = 158/3 = 52.7 g/eq. The equivalent weight changes with reaction conditions.