Molecular Formula Calculator
Convert an empirical formula into a true molecular formula using experimental molar mass data.
Simplest ratio (found via percent composition)
Mass found via experimentation (e.g. Mass Spec)
Common Examples
Ready to Calculate
Enter data to see the relationship between empirical and molecular formulas.
From Ratio to Reality
While the Empirical Formula tells you the simplest ratio of atoms, the Molecular Formula tells you the actual reality of the molecule. This calculator bridges that gap.
The Multiplier Method
Find 'n', then multiply all subscripts by it.
The Detectives Work
Imagine you found a mystery compound.
- Step 1**Combustion Analysis** tells you the ratio is 1 Carbon to 1 Hydrogen ($CH$). Mass = 13.
- Step 2**Mass Spectrometry** weighs the actual molecule and finds it weighs 78.
- Step 378 ÷ 13 = 6. So the real formula is $C_6H_6$ (**Benzene**).
Polymers & Plastics
This concept is the foundation of plastics.
A simple molecule like **Ethylene** ($C_2H_4$) acts as a monomer. If we link thousands of them together ($n \\approx 10,000$), we get **Polyethylene** — the plastic used in grocery bags and bottles.
In this case, 'n' isn't just a small number; it's the **degree of polymerization**, defining how long the plastic chain is.
Sugar vs. Vinegar
Glucose ($C_6H_12O_6$) and Acetic Acid ($C_2H_4O_2$) have the exact same Empirical Formula ($CH_2O$). Only by measuring Molar Mass can we tell sweet sugar apart from sour vinegar.
DNA Analysis
DNA is essentially a massive biopolymer. By analyzing the ratio of nucleotides (A, T, C, G) and the total mass, biochemists can characterize genetic fragments.
Drug Synthesis
When creating new medicines, chemists often synthesize a "crude" product. They find its empirical formula first (via combustion) and then confirm they made the right drug molecule using molar mass.
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Frequently Asked Questions
What is the difference between Empirical and Molecular Formula?
The Empirical Formula is the simplest whole-number ratio of atoms (e.g., $CH$ for Benzene). The Molecular Formula is the actual number of atoms in the real molecule (e.g., $C_6H_6$ for Benzene).
Why do I need Molar Mass?
The empirical formula only gives you a ratio. To know the 'true' formula, you need the total weight of the molecule (Molar Mass) to determine how many times that ratio repeats.
Can 'n' be a decimal?
No. Molecules must have whole numbers of atoms. If you calculate $n = 1.99$, it means your experimental data leads to $n = 2$. You should always round to the nearest whole integer.
What if n equals 1?
If $n = 1$, it means the Empirical Formula and Molecular Formula are identical. This is common for small molecules like Water ($H_2O$) or Carbon Dioxide ($CO_2$).
Can Empirical Mass be larger than Molar Mass?
No, that's chemically impossible. The Molar Mass must be equal to or a whole-number multiple of the Empirical Mass.
How is Molar Mass determined in a lab?
Chemists use techniques like Mass Spectrometry (weighing ions) or Colligative Properties (Freezing Point Depression) to find the experimental molar mass of an unknown substance.
Example: Finding formula for Vitamin C?
Empirical Formula = $C_3H_4O_3$ (Mass $\approx$ 88). Molar Mass = 176. 176 / 88 = 2. Multiply subscripts by 2 $\rightarrow$ $C_6H_8O_6$.
Is the molecular formula unique?
Usually yes for a given molar mass and empirical data. However, Isomers are different molecules that share the exact same molecular formula but have different structures.
Can I use this for polymers?
Yes! For polymers, 'n' represents the Degree of Polymerization—how many times the monomer unit repeats to form the plastic chain.
What if my Experimental Mass is slightly off?
Real lab data is rarely perfect. If you get $n = 2.05$, it's safe to assume $n = 2$. Our calculator shows you the rounded value (the multiplier) automatically.
How do I calculate Empirical Mass?
Just add up the atomic masses of the atoms in the Empirical Formula. For $CH_2O$: $C(12.01) + 2\times H(1.008) + O(16.00) = 30.03$ g/mol.
What is combustion analysis?
It's a common lab technique. You burn a substance and measure the $CO_2$ and $H_2O$ produced. This tells you the Empirical Formula. You then use this calculator to finish the job and find the Molecular Formula.