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Units of Concentration

Units of Concentration. A solution is a homogeneous mixture of one substance (the solute) dissolved in another substance (the solvent). Concentration is a ratio of the amount of solute to the amount of solvent. Units of Concentration. Percent volume

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Units of Concentration

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  1. Units of Concentration • A solution is a homogeneous mixture of one substance (the solute) dissolved in another substance (the solvent). • Concentration is a ratio of the amount of solute to the amount of solvent.

  2. Units of Concentration • Percent volume % volume = volume solute (ml) x 100 volume solution (ml) • Percent mass % mass = mass solute (g) x 100 mass solution (g) Solution = solvent + solute

  3. Units of Concentration Example 1: What is the percent by volume concentration of a solution in which 75.0 ml of ethanol is diluted to a volume of 250.0 ml? 75.0 ml x 100 = 30.0% 250.0 ml

  4. Units of Concentration Example 2: What volume of acetic acid is present in a bottle containing 350.0 ml of a solution which measures 5.00% concentration? x = 0.05 350.0 ml x = 17.5 ml

  5. Units of Concentration Example 3: Find the percent by mass in which 41.0 g of NaCl is dissolved in 331 grams of water. 41 g x 100 = 11.0% 372 g

  6. Units of Concentration • Molarity (M) is the most common unit of concentration • Molarity is an expression of moles/Liter of the solute.

  7. Units of Concentration • A mole is the SI unit of number of particles and can be used as an expression of the molecular weight of a substance. The formula weight of an element is expressed as grams/mole

  8. Units of Concentration • The molar mass of a compound can be calculated by adding the molar mass of the individual elements. 22.99 + 35.45 = 58.44 g/mol

  9. Making Solutions • You just calculated the molar mass of sodium chloride to be 58.44 g/mol. • To determine how to make a stock solution of sodium chloride, use the formula: g = M x L x molar mass

  10. Making Solutions • How many grams of NaCl would you need to prepare 200.0 mL of a 5 M solution? g = M x L x molar mass g = (5mol/L) (0.2L) (58.44g/mol) g = 58.44 g

  11. Diluting Solutions • Often once you have made a stock solution, you need to dilute it to a working concentration. • To determine how to dilute the stock solution, use the formula: C1 – concentration of stock C2 - concentration of diluted solution V1 – volume needed of stock V2 – final volume of dilution C1V1 = C2V2

  12. Diluting Solutions Example 5: How many milliliters of a 5 M stock solution of NaCl are needed to prepare 100 ml of a 0.4 M solution? C1 V1 = C2 V2 (5) V1 = (0.4)(100) V1= 8 ml

  13. Diluting Solutions • Serial Dilutions are dilutions made in series (for example, if you needed to make solutions that were 2M, 1M, 0.5M, and 0.25 M) • The formula for serial dilutions is: Dilution Factor = (V1 +V2) V1 V1 – volume of solution being diluted V2 – volume of solvent

  14. Units of Concentration Example 6: Propose a method to prepare 100 ml of a 0.5 M glucose solution from a 5 M glucose solution. 10 = (v1 + 100) v1 10v1 = v1 + 100 -v1 -v1 9v1 = 100 9 9 v1 = 11.1 ml of 5 M glucose + 100 ml H2O

  15. Diluting Solutions Dilutions tutorial

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