The Chemistry of Water

Water is a polar

molecule.

Has both + & – charges

The Chemistry of WaterH bond

1. When water molecules form hydrogen bonds with other water molecules.

Cohesion

Adhesion•H2O molecules form hydrogen bonds with other polar molecules.

•water climbs up fiber – ex. paper towel

Surface tension: Adhesion & Cohesion working

together•A property of liquid surfaces that causes the surface layer to behave like a thin elastic 'skin‘ & results in a downward pulling motion of water molecules.

Capillary Action:Adhesion & Cohesion working

together

The upward pull of water against gravity from plants roots to the leaves.

1. H2O molecules form hydrogen bonds with each other2. + attracted to –3. creates a ‘sticky’ molecule

The Chemistry of Water

Low Density of Ice• Most (all?) substances are more dense when they are solid

But not water…•Ice floats!

–H bonds form a crystalwith loose structure

Ice floats…..

ice floats because hydrogen bonds hold water molecules further apart in a solid than in a liquid

Why is it so impt that ice floats?•Oceans & lakes don’t freeze

solidif ice sank…

•eventually all ponds, lakes & even ocean would freeze solid•during summer, only upper few inches would thaw

•surface ice insulates water belowallowing life to survive the winter

Temperature Moderation•Organisms relay on heat of

vaporization to remove heat

Temperature Moderation•H2O resists changes in

temperature–takes a lot to heat it up

–takes a lot to cool it down

•H2O moderates temperatures on Earth

The Universal Solvent•H2O is a good solvent due to

its polarity• polar H2O molecules surround + & – ions• solvents dissolve solutes creating aqueous solutions•Saltwater; which is solute?

which is solvent?

The universal solvent

Questions1.What causes hydrogen bonds to

form between polar molecules?

(A) The atoms of polar molecules give up electrons to hydrogen atoms.

(B) Polar molecules have partially charged regions that attract other polar molecules. 

(C) The hydrogen atom in water molecules becomes negatively charged. 

(D) Hydrogen atoms in water molecules attract each other with positive charges.

Questions2. Which of the following properties of water is not caused by hydrogen bonding? 

(A) pH (B) cohesion (C) adhesion (D) surface tension

Questions3. What term describes the sugar in a glass of lemonade? 

(A) solvent (B) solution (C) solute (D) protein

Questions4. What is the relationship between hydrogen bonds and ionic bonds?

5. What determines whether a compound will dissolve in water?

6. How do polar molecules form hydrogen bonds?

Properties of Water Review

Ability to dissolve other substances

Creates surface tension

Exhibits capillary action

Low density of ice

Temperature moderation• Goldfish hibernate at the bottom of a pond in the

winter.• Humans cannot have too high of a fever or the

chemical reactions in their bodies will stop.• Land near large bodies of water stay warmer longer

in the fall then land away from large bodies of water.

Properties of Water Review

• Goldfish hibernate at the bottom of a pond in the winter.

• Humans cannot have too high of a fever or the chemical reactions in their bodies will stop.

• Land near large bodies of water stay warmer longer in the fall then land away from large bodies of water.