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CHM 2095 Lecture Notes - Lecture 3: Sodium Sulfide, Unified Atomic Mass Unit

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26 Aug 2016

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Na2s = 2(22. 99) + 32. 07 = 78. 05 amu. Mass % = mass part/mass whole * 100% This can also be used to find the % composition to identify a compound. Another way that mass percent can be used is to find how much of a compound that we need to get the desired amount of sub-molecular components. Example 1: how many grams of na2s do we need to obtain 20g of na? (2*22. 99)/78. 05 = 59% 20g na2s (59g na/100g na2s) = 11. 8g na. 20g na (100g na2s/59g na) = 34g na2s. This also works with alloys and non-bonded compounds. Example: in a silver coin, 90% of it is silver. 1 mole of he = 6. 022*10^23 atoms of he. 1 mole of h2o = 6. 022*10^23 atoms of h2o. 5 atoms o (1 mole o/6. 022*10^23 atom o) (16. 00grams o/1 mole o) The trick to avogadro"s number is that it converts amu to grams in a 1:1 ratio.

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