thursday, 19 th september 2013 today in chemistry percent composition assignment read pp. 320-355
DESCRIPTION
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.TRANSCRIPT
THURSDAY, 19TH SEPTEMBER 2013
•Today in Chemistry• Percent Composition
•Assignment•Read pp. 320-355
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)
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.
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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