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Chem 1100 Topic A Review Notes.docx

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Western University
Chemistry 1027A/B
Felix Lee

Topic A: Chemistry Review Isotope – elements with the same number of protons, but different number of neutrons, therefore they have different mass numbers Average Atomic Mass = ∑ (percent of isotopic abundance/100 x isotopic mass) Example: Silicon contains the following percent of isotopic abundances, what is the average atomic mass? Si-28: 92.23% Si-29: 4.67% Si-30: 3.10% Average Atomic Mass = (92.23/100 x 28) + (4.67/100 x 29) + (3.10/100 x 30) = 28.1u Cation – an atom that loses one or more electrons and becomes positively charged Anions – an atom that gains one or more electrons and becomes negatively charged 23 -1 Avagadro’s Number - # of atoms/molecules in one mole of a substance = 6.02x10 mol Example: Convert 1.85mol of C H O6to12t6ms. 23 24 (1.85mol)( 6.02x10 molecules/mole) = 1.11x10 molecules of C H O 6 12 6 (1.11x10 molecules)(6 + 12 + 6 atoms) = 2.67 x10 atoms in C H O 6 12 6 n (number of moles) = mass (g)/molar mass (gmol ) -1 Example: Find the number of moles in 12.29g of H O 2 n = 12.92g/18.02gmol = 0.72mol H O H2O 2 Mass Percent – percent of mass of one species in relation to the mass of the entire molecule Mass % = mass of one species/mass of sample x100 Example: Find the mass % of NaCl in a mixture of 13.77g NaCl and 30.29g NaNO . 3 Mass % NaCl = 13.77g/44.06g x100 = 31.25% Empirical Formula – the simplest ratio of atoms for a molecule (ex: the empirical formula of C H O is
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