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8A_Formulas

# 8A_Formulas - Molecular and Chemical Formulas Atoms...

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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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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.
Molecular weight To get the molecular formula, we need more information. Need: molecular weight.

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Empirical Formula from Analysis How do we determine the empirical formula? Start with mass % of elements (i.e. empirical data) and calculate a formula, or Start with the formula and calculate the mass % elements.
How to get empirical formulas PERCENT COMPOSITION % of element = % of element = 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 18.14 114.22 (atoms of element)(AW) FW of compound ! 100 100 sample g 100 element of mass !

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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 % 3 . 27 100 01 . 44 01 . 12 C % = ! = % 7 . 72 100 01 . 44 ) 0 . 16 ( 2 O % = ! = 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.
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8A_Formulas - Molecular and Chemical Formulas Atoms...

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