1 Chapter 7 Properties of Water

2 Structure of Water

3 Sources of Water on Earth

4 Properties of Water I – Freezing Point Both liquid and solid can be present together. H 2 O(s) → H 2 O(l) occurs at the same temperature as H 2 O(l) → H 2 O(s) 0 o C at normal atmospheric pressure. Heat of fusion = 334 J/g = 6.01 kJ/mol

5 Properties of Water II – Boiling Point The temperature at which the vapor pressure becomes equal to surrounding atmospheric pressure. 100 o C at 1 atmosphere. Highly pressure-dependent. Heat of vaporization = 2257 J/g = kJ/mol

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8 Properties of Water III – Specific Heat The amount of heat necessary to raise the temperature of one gram of a substance by 1 o C. S.H. of water = J/gK Higher for water than nearly any other substance. Heat capacity = heat needed to raise a given mass of substance 1 o C.

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10 Example: Example: Heat Capacity Calculate the heat necessary to raise the temperature of 250 mL of water from 23 o C to 75 o C. S.H. of water = J/gK

11 Solution: Solution: Heat Capacity Calculate the heat necessary to raise the temperature of 250 mL of water from 23 o C to 75 o C. = 54,400 J = 54.4 kJ = 54,400 J = 54.4 kJ

12 Water – The Universal Solvent

13 Solubility of Selected Alcohols in Water Alcohol Solubility (g/L) Name CH 3 OH Infinite methanol C 2 H 5 OH Infinite ethanol C 3 H 7 OH Infinite 1-propanol C 4 H 9 OH79 1-butanol C 5 H 11 OH27 1-pentanol C 6 H 13 OH hexanol C 7 H 15 OH heptanol

14 Colligative Properties Properties of a solution that are changed by the number of solute particles, rather than their nature. Vapor Pressure Boiling Point Elevation Freezing Point Depression Osmotic Pressure

15 Vapor Pressure of Pure Water and Water with a Solute

16 Boiling Point Elevation Freezing Point Depression  T b = K b x m K b for water = o C/m  T f = K f x m K f for water = 1.86 o C/m

17 Example: Example: Boiling Point Elevation Calculate the boiling point of a solution of 1.9 mol of sugar (C 12 H 22 O 11 ) dissolved in 400 g of water.  T b = K b x m K b for water = o C/m

18 Solution: Solution: Boiling Point Elevation Calculate the boiling point of a solution of 1.9 mol of sugar (C 12 H 22 O 11 ) dissolved in 400 g of water. molality = = m B.P elevation = o C/m x m = 2.4 o C Boiling Point =102.4 o C Boiling Point = = o C

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