CHM040 · Stoichiometry & Calculations · Classes 10–12
Percent Composition
Objective: To calculate the percentage by mass of each element in a compound.
🧪 Simulation — virtual model
🥧Percent Composition
🧰 Virtual materials and apparatus
- Virtual 3D pie chart
- IUPAC atomic masses
📐 Formulas and SI units
% element = (n × Aᵣ / M) × 100
💡 Theory
The mass percent of an element is its total atomic mass in the formula divided by the molar mass, times 100. For water: 2 × 1.008 / 18.015 × 100 = 11.19% hydrogen, so 88.81% oxygen. All percentages add up to 100.
🪜 Guided virtual procedure
- Choose water and read the hydrogen percentage.
- Compare the pie slices.
- Choose glucose and find the carbon percentage.
- Check that the percentages add to 100.
- Calculate one by hand.
📋 Observations Simulated values
✅ Result and conclusion
Water is 11.19% hydrogen and 88.81% oxygen by mass.
🔬 Real lab vs simulation
Real compositions are measured by elemental analysis and agree with the formula within about 0.3%.
⚠️ Safety
Calculation only. Real laboratory chemicals are handled only by teachers in a school laboratory.
❓ Quick check
1. % C in CO₂?
2. % Na in NaCl?
3. The percentages always add to…
🏋️ Practice
Easy% O in CaCO₃?
Answer: 48.0%
Medium% N in NH₃?
Answer: 82.2%
Challenge% C in glucose?
Answer: 40.0%