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Concentration

Concentration. A primer. Definitions. Concentration is the amount of something mixed with other things in a space. The “amount” can be in grams, molecules, ions or moles The “other things” can be described as a volume, or a mass or number of moles of a material

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Concentration

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  1. Concentration A primer

  2. Definitions • Concentration is the amount of something mixed with other things in a space. • The “amount” can be in grams, molecules, ions or moles • The “other things” can be described as a volume, or a mass or number of moles of a material • Most of the time it describes the amount of stuff dissolved in a liquid.

  3. Solutions • Solutions have two parts • A solute (often solid) • A solvent • Together they make a solution • Notice that: • The solute “disappears” • The properties of the solvent change • The volume of the solution is greater than the solvent

  4. Ways to think about concentration • “Concentrated” means there is a lot of stuff packed together tightly • In a way, it is similar to density (mass/ volume), but concentration deals with mixtures, not pure materials • Remember, in any solution there are three parts: • a solute (the thing being added), • the solvent (the mixer) • and the solution (the two combined)

  5. Formulas(Many of them!) • Molarity (M) = moles solute/ Liter solution • Molality (m) = moles solute/ kilogram solvent • Mole Fraction (c“chi”) = moles solute/ total moles solution • % concentration = grams solute/ 100 grams solvent • Parts per million (ppm) = number molecules / million molecules solution (or mole fraction x 106) • Normal (N) = moles of ions / Liter solution

  6. Ways to use formulas • In stoichiometry…one needs to convert volumes of a solution to moles • Concentration(M) x Volume (Liters) = moles • In dilutions, one adds more solvent (Liters) to get a less concentrated solution, the moles solute remain the same • Conc (M) x Volume = moles = Conc (M) x Volume (L)

  7. Molar Calculations • Volume needed to get 0.3 moles of a 6 Molar solution? • 6 M = 0.3 moles/ X liters • X= 0.05 Liters • You want 2 Liters of a 0.1 Molar solution and you have a 1 molar solution. How much is needed? • Concentration x volume = conc x volume • 0.1 Molar x 2 Liters = 1 Molar x X volume • X = 0.2 Liters (200 mL)

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