6_8A_Formulas - Molecular and Chemical Formulas Atoms...

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MJ Bojan Chem 110 FA 2010 1 Molecular and Chemical Formulas Atoms combine (bond) to form molecules. Each molecule has a chemical formula. The chemical formula indicates which atoms are found in the molecule, and in what proportion they are found.
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MJ Bojan Chem 110 FA 2010 2 CHEMICAL FORMULA Formula that gives the TOTAL number of elements in a molecule or formula unit. EMPIRICAL FORMULA Chemical formula with the smallest integer subscripts for a given composition.
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MJ Bojan Chem 110 FA 2010 3 Molecular weight To get the molecular formula, we need more information. Need: molecular weight. MOLAR MASS or FORMULA WEIGHT sum of atomic weights The connection between experimental property (mass) and moles: C 8 H 18 8 C 12.01 96.08 18H 1.008 18.14
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MJ Bojan Chem 110 FA 2010 4 PERCENT COMPOSITION % of element = What is the mass percent of C in CO 2 ? C = 12.01 amu O = 16.0 amu FW =12.01 + 2(16.0) = 44.01 amu
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MJ Bojan Chem 110 FA 2010 5 I have 2g of a sample that is 54.2% C by mass. How many grams of C are in the sample? HINT: If % C in an unknown substance is 54.2%, a 100g sample of that substance contains 54.2g of C. % of element = PERCENT COMPOSITION
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MJ Bojan Chem 110 FA 2010 6 Empirical Formula from Analysis Find mass of each component in a sample. Use ____________ to find mole ratio of atoms. Mole ratio gives empirical formula Molecular weight (obtained from a separate experiment) can be used to get How do we determine the empirical formula?
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