Authoritative Data Source and Methodology
Primary source: Commission on Isotopic Abundances and Atomic Weights (CIAAW), “Standard Atomic Weights 2021.” Secondary reference: NIST Chemistry WebBook. All atomic weights are conventional values suitable for general laboratory calculations.
Statement: Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da queste fonti.
Statement: Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da queste fonti.
The Formula Explained
For a compound composed of elements \( E_i \) with stoichiometric coefficients \( n_i \), the molar mass \( M \) is:
\( M = \sum_i n_i \, A_r(E_i) \quad [\mathrm{g \, mol^{-1}}] \)
The mass percent of element \( i \) is:
\( w_i(\%) = \dfrac{n_i \, A_r(E_i)}{\sum_j n_j \, A_r(E_j)} \times 100 \)
\( M = \sum_i n_i \, A_r(E_i) \quad [\mathrm{g \, mol^{-1}}] \)
The mass percent of element \( i \) is:
\( w_i(\%) = \dfrac{n_i \, A_r(E_i)}{\sum_j n_j \, A_r(E_j)} \times 100 \)
Worked Example
Formula: C8H10N4O2 (caffeine).
Multiply each atomic weight by its count and sum: 194.194 g/mol. The tool also reports percent composition and empirical formula.
Frequently Asked Questions
Does the calculator support hydrates and nested groups?
Yes. Use middle dots for hydrates (CuSO4·5H2O) and parentheses or brackets for nested groups (Ca3(PO4)2, K4[Fe(CN)6]).
Why might my value differ from literature?
Atomic weights can vary slightly by source. We use CIAAW conventional values; studies using isotopic composition or exact masses may report different figures.
Can I include isotopes or charges?
Isotopic prefixes (e.g., 13C) are ignored; charge does not affect molar mass in this calculator. For isotope-specific work, use a mass spectrometry tool.