Chemistry
Rounding Atomic Mass Too Early
Students round atomic masses to whole numbers before finishing molar mass or percent-composition calculations.
Quick check
Why students make it
Periodic tables often show values near whole numbers, so students think the nearest integer is the official mass. They also try to make arithmetic easier before the final answer.
The rule done right
Use the atomic masses from the periodic table throughout the calculation and round only the final answer to the correct significant figures. If a teacher gives a rounded mass, use that given value consistently.
Related resources
-
Chemistry, Significant Figures in Chemistry Infographic -
Chemistry, Percent Composition Infographic -
Mole Concept (Visual Conversions) Infographic -
Chemistry, Empirical vs Molecular Formula Infographic -
Stoichiometry Roadmap Infographic - Stoichiometry & Molar Mass Cheat Sheet
- Percent Composition and Hydrate Formula Worked Examples Cheat Sheet
- Empirical vs Molecular Formula Cheat Sheet
- Mole Conversion Roadmap Cheat Sheet
- Avogadro's Number and the Mole Concept Worked Examples Cheat Sheet
- Science, Stoichiometry Calculations Worksheet
- Science, The Mole and Avogadros Number Worksheet
- Science, Solution Chemistry, Molarity and Concentration Worksheet
- Significant Figures Calculator Tool
- Molar Mass & Stoichiometry Calculator Tool
- Empirical & Molecular Formula Calculator Tool
- Mole Converter & Gas Stoichiometry Tool
- Periodic Table Explorer Tool
- Stoichiometry Lab Lab
- Limiting Reactant & Percent Yield Lab Lab
- Gravimetric Analysis Lab Lab