Chapter 17: Water and Aqueous Systems

Ms. Knick HAHS

CHEM 1B

Chapter 17 Section 1Liquid Water and Its Properties:

-it is foundation of all life

-makes up 70% of body of humans

-can exist in all three phases

-Water is polar

-bonding e- shared unequally

*caused by electronegativity diff.

-Many properties of water are due to hydrogen bonding

-water has strong attractions between the hydrogen atoms and oxygen atoms of different water molecules and it is very

difficult to break these bonds

Properties Resulting From H-Bonding

1) high surface tension

2) Low Vapor Pressure

3) high heat of vaporization

4) high boiling point

Surface Properties

-surface of water acts as a skin

--this is explained by surface tension:

-inward force or pull that tends to minimize the surface area of a liquid

-holds water in shape of sphere

-can be reduced by adding a surfactant: interferes with hydrogen bonding

ex- soap

Low Vapor Pressure

vapor pressure- pressure right above the surface of a liquid, caused by molecules escaping to gas phase

-b/c of H-bonding the molecules cannot escape as easily so vapor pressure is low

-if not lakes, ponds, oceans would easily evaporate

Chapter 17 Section 2• -Water has a high heat of vaporization

-this is the amount of energy needed to convert 1g of a liquid to gas at the boiling pt.

• -difficult to break bonds to vaporize water due to THE STRONG H-BONDS.

• Because of hydrogen bonding, the heat of vaporization is higher than most other substances.

• Iron’s heat of vaporization is only 0.447, which means for the same increase in temp as water, Fe only need 0.447 units of energy.

• Water’s high heat of vaporization (4.184) helps to moderate daily air temperature around large bodies of water

-opposite of vap. is known as the heat of condensation (g→ℓ)

-boiling point of water is high b/c of H- bonding-it takes more heat to disrupt molecules

*Read page 480 and write a few sentences describing ice- solid water

Chapter 17 Section 3

aqueous solution- water sample containing dissolved substances

solvent- dissolving medium, what does the dissolving

*water is known as the universal solvent

solute- what is being dissolved

ex- water and ice tea mix

solutions are homogeneous mixtures-

-the same throughout, uniform in composition, cannot pick out individual pieces

-solute particles in a solution are small→ ≈1nm

solvation- process that occurs when a solute dissolves, solute particles become surrounded by solvent

-some substances are insoluble- not able to be dissolved

-this is b/c their attractions are stronger than water

-Why does oil not dissolve in water?

-because polar molecules only dissolve other polar molecules, nonpolar only dissolve nonpolar

-“like dissolves like”

electrolyte- conducts an electric current in aqueous solution or the molten state

-ionic compounds are electrolytes

weak electrolyte- when in solution only a fraction of the solute exists as ions

strong electrolyte- when dissolved almost all of the solute exists as separate ions

nonelectrolyte- do not conduct an electric current in aqueous or molten state

hygroscopic- salts and other compounds that remove moisture from the air

desiccant- hygroscopic substances used as drying agents

ex- packets found in shoe boxes, beef jerky

-some compounds are so hygroscopic that they become wet when exposed to moist air

deliquescent compounds- remove water from air to dissolve completely and form solutions

ex- NaOH