Chapter 4

# Chapter 4 - Chapter 4  Mole  •...

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Unformatted text preview: Chapter 4  Mole  • Contains 6.022 × 1022 (Avogadro’s number) atoms, molecules, or formula units  • Abbreviated mol  Molar Mass  • The mass of one mole of a substance  • Found by adding the atomic masses together (H2O H=1.01, O=15.99, so H2O=18.01)  • Abbreviated MM  Moles from Mass  • When you are given the grams of a substance, but need to convert to moles you use the molar  mass (1.27g Cu ×         = 0.0200 moles Cu) Note: notice that the proper units cancel  Number of atoms,  molecules, or  formula units  Mass in grams  MM  Moles  Avogadro’s  number  Percent Composition by Mass  • An expression of the portion of the total mass contributed by each element  • Found by dividing the part by the whole and multiplying by 100.  For example: To find the  percent of 1.27 g Cu in a 3.67 g sample of chalcopyrite use   Cu  Empirical Formula  • Expresses the simplest ratios of atoms in a compound  • Written with the smallest whole number subscripts, basically reduce by the largest common  denominator (C5H10 becomes CH2 but H2S remains H2S because it is already “reduced”)  Empirical Formula from Percent Composition    % A  Mass of compound  Mass A  MM of A  Moles A  Empirical  formula          Mass of compound    MM of B  % B  Mass B    Molarity  • Most common way to express concentration  • The number of moles dissolved into one liter of solution  • Abbreviated M (note the italics)  • Molarity =       Moles B    Molarity of Solutions      Mass from Molarity    Grams of solute  MM  Moles of solute  volume  Molarity  Molarity  volume  Moles of solute  MM  Grams of solute    Solution  • • • • Solution – any mixture that is homogeneous at the molecular or ionic scale  Solvent – the substance doing the dissolving (usually water)  Solute – the substance in a solution that is dissolved into solution (usually smaller amount than  solvent)  Dilute vs Concentration – dilute solutions contain small amounts of solute, where concentrated  solutions contain large amounts of solute  Dilution  • • The process of lowering the concentration of a solution by adding more solvent.  Found by the formula M1V1=M2V2   ...
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