Download - THURSDAY, 19 TH SEPTEMBER 2013 Today in Chemistry Percent Composition Assignment Read pp. 320-355
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THURSDAY, 19TH SEPTEMBER 2013
•Today in Chemistry• Percent Composition
•Assignment•Read pp. 320-355
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KEY IDEA
•Formula mass = The sum of the atomic masses in the formula. KNO3
K = 39.1 amuN = 14.0 amuO = 3 x 16.0 amuKNO3 101.1 amu
AMU?Atomic Mass Unit 39.1 g of K is equal to 14.0 g of N (same # of particles)
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KEY IDEA
•The law of Definite Proportions
A compound is always composed of the same elements in the same proportion by mass, no matter how large or small the sample.
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KEY IDEA
•Percent Composition~Remember it adds up to 100% Percent Composition by Mass% Comp. = # Atoms x Atomic Mass x
100Formula Mass
% H in H2O = 2 atoms H x 1.0 amu x 10018.0 amu H2O
% H in H2O = 11 % So…. %O = ?
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KEY IDEA
• The Law of Multiple ProportionsWhen different compounds are formed by the same elements, different masses combine in simple whole number ratios. Methane CH4 Ethane C2H6
FM = 16.0 FM = 30 % H = 25% % H = 20%
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