Equivalent Weight Calculator
Discover the simplicity of chemistry with examples.com's Equivalent Weight Calculator. Accurate, efficient, and easy to use!
How to Use the Equivalent Weight Calculator
- Choose Basic Calculator or Advanced Calculator.
- For Basic: enter the Molecular Weight (MW) and ΔE (electrons gained or lost).
- For Advanced: enter the Total Molecular Weight, Total ΔE, and Number of Atoms in the compound.
- Click “Calculate” to see the result instantly.
Features of the Equivalent Weight Calculator
- Basic mode calculates equivalent weight from molecular weight and ΔE.
- Advanced mode calculates the average equivalent weight per atom across a whole compound.
- Instant, live results as you type.
- Free to use with no sign-up required.
Equivalent Weight Formula
The equivalent weight (EW) of a substance is its molecular weight divided by the number of electrons it gains or loses in a reaction (ΔE), also called its valence factor.
Equivalent Weight (EW) = Molecular Weight (MW) ÷ ΔE
For a full compound made up of multiple atoms, the average equivalent weight per atom is found by also dividing by the total number of atoms in the compound:
Average Equivalent Weight per Atom = Total Molecular Weight ÷ (Total ΔE × Number of Atoms)
Equivalent Weight Reference Table
| Molecular Weight (MW) | ΔE | Equivalent Weight (EW) |
|---|---|---|
| 40 | 1 | 40 |
| 56 | 1 | 56 |
| 74 | 2 | 37 |
| 98 | 2 | 49 |
| 106 | 2 | 53 |
| 158 | 5 | 31.6 |
| 294 | 6 | 49 |
How to Calculate Equivalent Weight
To find equivalent weight, divide the molecular weight of the substance by the number of electrons it gains or loses during a chemical reaction, known as ΔE or the valence factor.
Suppose you have a compound with a molecular weight of 98 and a ΔE of 2. 98 ÷ 2 = 49.
Thus, the equivalent weight is 49.
Solved Examples on Equivalent Weight
1. Basic Equivalent Weight Calculation
Example: Find the equivalent weight of a substance with MW = 106 and ΔE = 2.
EW = 106 ÷ 2 = 53.
2. Equivalent Weight With a Higher Valence Factor
Example: Find the equivalent weight of a substance with MW = 294 and ΔE = 6.
EW = 294 ÷ 6 = 49.
3. Average Equivalent Weight per Atom
Example: Find the average equivalent weight per atom for a compound with Total MW = 2101, Total ΔE = 523, and 52 atoms.
Average EW per atom = 2101 ÷ (523 × 52) = 2101 ÷ 27,196 ≈ 0.0772540079.
4. Equivalent Weight With a Decimal Result
Example: Find the equivalent weight of a substance with MW = 158 and ΔE = 5.
EW = 158 ÷ 5 = 31.6.
1. What is equivalent weight?
Equivalent weight is the mass of a substance that combines with or displaces a fixed quantity of another substance, calculated as molecular weight divided by the number of electrons the substance gains or loses (ΔE).
2. What is ΔE in the equivalent weight formula?
ΔE, also called the valence factor, is the number of electrons gained or lost, protons replaced, or charge change involved when the substance reacts — for example, ΔE = 2 for a substance that loses two electrons per molecule.
3. How is average equivalent weight per atom different from equivalent weight?
Standard equivalent weight applies to a whole molecule. Average equivalent weight per atom spreads that value across every atom in the compound by also dividing by the total atom count, useful when comparing weight contribution on a per-atom basis.
4. Can equivalent weight be a decimal?
Yes. Equivalent weight is only a whole number when molecular weight is evenly divisible by ΔE — otherwise the result is a decimal, as in the case of MW = 158 and ΔE = 5, which gives 31.6.
5. Why is equivalent weight important in chemistry?
Equivalent weight is used in titrations, acid-base reactions, and redox reactions to determine how much of one substance reacts with a fixed amount of another, independent of the specific reaction’s stoichiometric coefficients.
6. Does ΔE change for the same compound?
Yes, ΔE can differ depending on the reaction the compound is undergoing, since the same substance may gain or lose a different number of electrons in different reactions.