16 4 Calculations Involving Colligative Properties Molality and

16. 4 Calculations Involving Colligative Properties > Molality and Mole Fraction What are two ways of expressing the concentration of a solution? Slide 1 of 42 © Copyright Pearson Prentice Hall

16. 4 Calculations Involving Colligative Properties > Molality and Mole Fraction The unit molality and mole fractions are two additional ways in which chemists express the concentration of a solution. Slide 2 of 42 © Copyright Pearson Prentice Hall

16. 4 Calculations Involving Colligative Properties > Molality and Mole Fraction The unit molality (m) is the number of moles of solute dissolved in 1 kilogram (1000 g) of solvent. Molality is also known as molal concentration. Slide 3 of 42 © Copyright Pearson Prentice Hall

16. 4 Calculations Involving Colligative Properties > Molality and Mole Fraction To make a 0. 500 m solution of Na. Cl, use a balance to measure 1. 000 kg of water and add 0. 500 mol (29. 3 g) of Na. Cl. Slide 4 of 42 © Copyright Pearson Prentice Hall

16. 4 Calculations Involving Colligative Properties > Molality and Mole Fraction Ethlylene Glycol (EG) is added to water as antifreeze. Slide 5 of 42 © Copyright Pearson Prentice Hall

SAMPLE PROBLEM 16. 6 Slide 6 of 42 © Copyright Pearson Prentice Hall

SAMPLE PROBLEM 16. 6 Slide 7 of 42 © Copyright Pearson Prentice Hall

SAMPLE PROBLEM 16. 6 Slide 8 of 42 © Copyright Pearson Prentice Hall

16. 4 Calculations Involving Colligative Properties > Molality and Mole Fraction The mole fraction of a solute in a solution is the ratio of the moles of that solute to the total number of moles of solvent and solute. Slide 9 of 42 © Copyright Pearson Prentice Hall

16. 4 Calculations Involving Colligative Properties > Molality and Mole Fraction In a solution containing n. A mol of solute A and n. B mol of solvent B (XB), the mole fraction of solute A (XA) and the mole fraction of solvent B (XB) can be expressed as follows. Slide 10 of 42 © Copyright Pearson Prentice Hall

SAMPLE PROBLEM 16. 7 Slide 11 of 42 © Copyright Pearson Prentice Hall

SAMPLE PROBLEM 16. 7 Slide 12 of 42 © Copyright Pearson Prentice Hall

SAMPLE PROBLEM 16. 7 Slide 13 of 42 © Copyright Pearson Prentice Hall

16. 4 Calculations Involving Colligative Properties > Freezing-Point Depression and Boiling-Point Elevation Freezing-Point Depression and Boiling. Point Elevation How are freezing-point depression and boiling-point elevation related to molality? Slide 14 of 42 © Copyright Pearson Prentice Hall

16. 4 Calculations Involving Colligative Properties > Freezing-Point Depression and Boiling-Point Elevation The magnitudes of the freezing-point depression and the boiling-point elevation of a solution are directly proportional to the molal concentration (m), when the solute is molecular, not ionic. Slide 15 of 42 © Copyright Pearson Prentice Hall

16. 4 Calculations Involving Colligative Properties > Freezing-Point Depression and Boiling-Point Elevation The constant, Kf, is the molal freezing-point depression constant, which is equal to the change in freezing point for a 1 -molal solution of a nonvolatile molecular solute. Slide 16 of 42 © Copyright Pearson Prentice Hall

16. 4 Calculations Involving Colligative Properties > Freezing-Point Depression and Boiling-Point Elevation Slide 17 of 42 © Copyright Pearson Prentice Hall

16. 4 Calculations Involving Colligative Properties > Freezing-Point Depression and Boiling-Point Elevation The constant, Kb, is the molal boiling-point elevation constant, which is equal to the change in boiling point for a 1 -molal solution of a nonvolatile molecular solute. Slide 18 of 42 © Copyright Pearson Prentice Hall

16. 4 Calculations Involving Colligative Properties > Freezing-Point Depression and Boiling-Point Elevation Slide 19 of 42 © Copyright Pearson Prentice Hall

16. 4 Calculations Involving Colligative Properties > Freezing-Point Depression and Boiling-Point Elevation Slide 20 of 42 © Copyright Pearson Prentice Hall

SAMPLE PROBLEM 16. 8 Slide 21 of 42 © Copyright Pearson Prentice Hall

SAMPLE PROBLEM 16. 8 Slide 22 of 42 © Copyright Pearson Prentice Hall

SAMPLE PROBLEM 16. 8 Slide 23 of 42 © Copyright Pearson Prentice Hall

SAMPLE PROBLEM 16. 9 Slide 24 of 42 © Copyright Pearson Prentice Hall

SAMPLE PROBLEM 16. 9 Slide 25 of 42 © Copyright Pearson Prentice Hall

SAMPLE PROBLEM 16. 9 Slide 26 of 42 © Copyright Pearson Prentice Hall