🎓 Chemistry • Stoichiometry
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Percent Composition Calculator
Computes elemental mass percentages from chemical formulas with interactive stacked mass fraction diagrams.
Chemical Formula Evaluator
Supports brackets, parenthesis, and hydrates (e.g. Ca(OH)₂, C₆H₁₂O₆, CuSO₄·5H₂O)
Total Molar Mass (Molecular Weight)
180.156 g/mol
Unified Mass (u / Da)
180.156 u
SI Molar Mass
0.180156 kg/mol
Total Atoms
24 atoms/molecule
Empirical Formula
CH2O
Visual Mass Fraction Breakdown
Total180.156g/mol
O (Oxygen)
53.3%
C (Carbon)
40.0%
H (Hydrogen)
6.7%
| Element | Atoms (n) | Standard Weight | Subtotal Mass | Mass Percent |
|---|---|---|---|---|
| O Oxygen Z = 8 • nonmetal | 6 | 15.999 | 95.994 g/mol | 53.28% |
| C Carbon Z = 6 • nonmetal | 6 | 12.011 | 72.066 g/mol | 40.00% |
| H Hydrogen Z = 1 • nonmetal | 12 | 1.008 | 12.096 g/mol | 6.71% |
Complete Chemical & Mathematical Derivation
1. Formula Decomposition: Found 3 unique elements totaling 24 atoms per formula unit. 2. Element-by-Element Mass Contributions: • Oxygen (O, Z=8): 6 atoms × 15.999 g/mol = 95.9940 g/mol (53.28%) • Carbon (C, Z=6): 6 atoms × 12.011 g/mol = 72.0660 g/mol (40.00%) • Hydrogen (H, Z=1): 12 atoms × 1.008 g/mol = 12.0960 g/mol (6.71%) 3. Total Molecular Mass: M = 95.994 + 72.066 + 12.096 = 180.1560 g/mol 4. Empirical Formula: CH2O (Common divisor = 6)
What is Percent Composition by Mass?
Percent composition is the percentage by mass of each element in a compound, crucial for verifying chemical formulas.
Formula & Step-by-Step Calculation
% Element = (Mass of Element in 1 mol / Molar Mass of Compound) × 100%
Ratio of elemental subtotal mass to total compound molar mass.
Worked Step-by-Step Examples
Example 1
Percent composition of Water (H2O)
Solution: H: 11.19%, O: 88.81%
• H: (2.016 / 18.015) × 100 = 11.19%; O: (15.999 / 18.015) × 100 = 88.81%
Common Real-World & Academic Use Cases
- ✓ Elemental CHN combustion analysis
- ✓ Mineral ore assay grading
- ✓ Fertilizer N-P-K nutrient analysis
How to Use the Percent Composition Calculator
1
Enter Chemical Formula
Input formula notation.
2
View Percentages
Review element-by-element % mass breakdown.
Frequently Asked Questions
Q: Should the sum of mass percentages always equal 100%?
Yes, the sum of all constituent elements must equal 100% (within rounding precision).