Solution Concentration Section 15 2 Objectives Review You

Solution Concentration Section 15. 2 Objectives:

Review You have 1500. 0 g of a bleach solution. The percent by mass of the solute Na. Cl. O is 3. 62%. How many grams of Na. Cl. O are in the solution? 2. How many grams of solvent are in the solution? 3. What is the percent by volume of isopropyl alcohol in a solution that contains 24 m. L of isopropyl alcohol in 1. 1 L of water? 1.

Expressing Concentration 1. 2. 3. 4. 5. % by mass % by volume Molarity Molality Mole fraction

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.

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?

Preparing Molar Solutions What does “ 2 M Na. OH soln” mean? Answer: 2 moles Na. OH/1 L soln So how would you prepare 100 m. L of 2 M Na. OH? 1. Determine the number of moles of Na. OH in 100 m. L of solution. 2. Convert to grams of Na. OH needed. 3. Add the Na. OH to a flask, THEN add distilled water to the required volume. WHY do we add solute FIRST?

Bellringer What does a 3. 00 M KI solution contain? 2. If M 1 V 1 = M 2 V 2, how much of the 3. 00 M KI soln would you need to make 0. 300 L of a 1. 25 M KI soln? 1. This is how you dilute a soln to make a soln of less concentration! AND you have just done Practice Problem #21, p. 468.

Assignment – Part A P. 485: 80 -82

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.

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 Na 2 SO 4 dissolved in 1000. 0 g of water? Example 2 (#25): What is the molality of a soln containing 30. 0 g C 10 H 8 dissolved in 500. 0 g of toluene?

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 = ____n. A____ (n. A + n. B) So what does XB equal? ? ?

Molality and Mole Fraction, continued……… Example 1 (#26, p. 470): What is the mole fraction of Na. OH in an aqueous soln that contains 22. 8% Na. OH by mass? Example 2(#27): An aqueous soln of Na. Cl has a mole fraction of 0. 21. What is the mass of Na. Cl dissolved in 100. 0 m. L of solution?

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