Chapter 17: Water and Aqueous Systems Ms. Knick HAHS CHEM 1B

Chapter 17 Section 1 Liquid 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 high surface tension Low Vapor Pressure high heat of vaporization 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