Chapter 7

1

Chapter 7Chapter 7

Properties of WaterProperties of Water

2

Structure of Water

O

HH

....

3

Sources of Water on Earth

4

Properties of Water I – Freezing Point Both liquid and solid can be present

together.

H2O(s) → H2O(l)

occurs at the same temperature as

H2O(l) → H2O(s)

0oC 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.

100oC at 1 atmosphere.

Highly pressure-dependent.

Heat of vaporization = 2257 J/g = 40.67 kJ/mol

6

7

8

Properties of Water III –

Specific Heat The amount of heat necessary to raise

the temperature of one gram of a substance by 1oC.

S.H. of water = 4.184 J/gK Higher for water than nearly any other

substance. Heat capacity = heat needed to raise a

given mass of substance 1oC.

9

10

Example: Example: Heat Capacity

Calculate the heat necessary to raise the temperature of 250 mL of water from 23oC to 75oC.

S.H. of water = 4.184 J/gK

11

Solution: Solution: Heat Capacity

Calculate the heat necessary to raise the temperature of 250 mL of water from 23oC to 75oC.

= 54,400 J = 54.4 kJ= 54,400 J = 54.4 kJ

C52 x Cg

J 4.184 x

mL 1

g 1 x mL 250 o

o

12

Water – The Universal Solvent

13

Solubility of Selected Alcohols in WaterAlcohol Solubility (g/L) Name

CH3OH Infinite methanol

C2H5OH Infinite ethanol

C3H7OH Infinite 1-propanol

C4H9OH 79 1-butanol

C5H11OH 27 1-pentanol

C6H13OH 5.9 1-hexanol

C7H15OH 0.9 1-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 ElevationFreezing Point Depression

Tb = Kb x m

Kb for water = 0.512 oC/m

Tf = Kf x m

Kf for water = 1.86 oC/m

17

Example:Example: Boiling Point Elevation

Calculate the boiling point of a solution of 1.9 mol of sugar (C12H22O11) dissolved in 400 g of water.

Tb = Kb x m

Kb for water = 0.512 oC/m

18

Solution:Solution: Boiling Point Elevation

Calculate the boiling point of a solution of 1.9 mol of sugar (C12H22O11) dissolved in 400 g of water.

molality = = 4.75 m

B.P elevation = 0.512 oC/m x 4.75 m = 2.4 oC

Boiling Point =Boiling Point = 100 + 2.4 = 102.4102.4ooCC

waterkg 0.400

sugar mol 91.

19