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Solution Concentration Section 15.2

Solution Concentration Section 15.2. Objectives:. Review. You have 1500.0 g of a bleach solution. The percent by mass of the solute NaClO is 3.62%. How many grams of NaClO are in the solution? How many grams of solvent are in the solution?

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Solution Concentration Section 15.2

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  1. Solution Concentration Section 15.2 Objectives:

  2. Review • You have 1500.0 g of a bleach solution. The percent by mass of the solute NaClO is 3.62%. How many grams of NaClO are in the solution? • How many grams of solvent are in the solution? • What is the percent by volume of isopropyl alcohol in a solution that contains 24 mL of isopropyl alcohol in 1.1 L of water?

  3. Expressing Concentration • % by mass • % by volume • Molarity • Molality • Mole fraction

  4. Molarity (M) • Definition: the number of moles of solute dissolved in one liter of solution. • What would the units be? Answer: moles/L, but we just use M, for “molar” • This is how most chemical solns are described.

  5. Molarity, continued……… • Example: What is the molarity of an aqueous soln containing 40.0 g of glucose in 1.5 L of soln? • What are the actual units for molarity? • So what 2 things do we need to have? • What 2 things are we GIVEN in this problem? • How do we get from what we HAVE to what we NEED?

  6. Preparing Molar Solutions • What does “2M NaOHsoln” mean? Answer: 2 moles NaOH/1 L soln • So how would you prepare 100 mL of 2M NaOH? • Determine the number of moles of NaOH in 100 mL of solution. • Convert to grams of NaOH needed. • Add the NaOH to a flask, THEN add distilled water to the required volume. • WHY do we add solute FIRST?

  7. Bellringer • What does a 3.00M KI solution contain? • If M1V1 = M2V2, how much of the 3.00M KI soln would you need to make 0.300 L of a 1.25M KI soln? • This is how you dilute a soln to make a soln of less concentration! • AND you have just done Practice Problem #21, p.468. 

  8. Assignment – Part A • P.485: 80-82

  9. Molality and Mole Fraction • What happens to the volume of a solution as the temperature increases? • So what would happen to its molarity? • Did the moles (or mass) of solute change? • Did the MASS of the solvent change? • So molarity changes, but masses do not.

  10. Molality and Mole Fraction, continued……… • Molality (m): the ratio(?) of the number of moles of solute dissolved in one kg of solvent • So m = ????? • Example 1 (#24, p.469): What is the molality of a soln containing 10.0 g Na2SO4 dissolved in 1000.0 g of water? • Example 2 (#25): What is the molality of a soln containing 30.0 g C10H8dissolved in 500.0 g of toluene?

  11. Molality and Mole Fraction, continued……… • Mole fraction (X): the ratio of the number of moles of solute in solution to the TOTAL number of moles of solute AND solvent. • XA represents the mole fraction of the solvent • XB represents the mole fraction of the solute • XA = ____nA____ (nA + nB) • So what does XB equal?????

  12. Molality and Mole Fraction, continued……… • Example 1 (#26, p.470): What is the mole fraction of NaOH in an aqueous soln that contains 22.8% NaOH by mass? • Example 2(#27): An aqueous soln of NaCl has a mole fraction of 0.21. What is the mass of NaCl dissolved in 100.0 mL of solution?

  13. Assignment – Part B • P.485: 83-85 • Study Guide for Content Mastery workbook: pp.86-88

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