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Chapter 5 Chemistry Notes

This is the relative number of hs and os more about

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Unformatted text preview: of H’s and O’s, more about this in Ch. 6) Application: Law of Constant Composition Chemical Formula We write a Chemical Formula to summarize the elements present in the compound, e.g. H2O. Two Samples of Iron oxide are found, each decomposed to Fe and O use elemental symbol for each atom in compound use subscript to indicate number of atoms of each type. ( “1” is implied if nothing written, and use parentheses when needed.) Elements are written in this order: (metal left, non-metal right) F O Left most Examples: NaCl not ClNa CO2 not O2C CHCl3 not HCl3C or Cl3CH, etc. (exception, OH-) Mass Fe (g) To Right most 167.54 72.00 Sample 2 Mass O (g) Sample 1 125.65 48.00 Are they the same Iron Oxide? Look at the mass ratios: amu amu mass Fe 167.53 g Fe 125.65 g Fe = = 2.327 ≠ 2.618 = mass O 72.00 g O amu 48.00 g O amu Analysis: based on 4 sig figs, ratios are different. Conclusion: Not the same Iron Oxide! (FYI: Hematite, Fe2O3 vs Magnetite, Fe3O4 , notice how chemical formulas are often a more meaningful summary than masses). http://old.iupac.org/publications/books/princip...
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