The Chemistry of Water

Water is a polar molecule. Has both + & – charges The Chemistry of Water H 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. H 2 O molecules form hydrogen bonds with each other 2. + 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 crystal with 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 solid if ice sank… eventually all ponds, lakes & even ocean would freeze solid during summer, only upper few inches would thaw surface ice insulates water below allowing life to survive the winter

Temperature Moderation Organisms relay on heat of vaporization to remove heat

Temperature Moderation H 2 O resists changes in temperature –takes a lot to heat it up –takes a lot to cool it down H 2 O moderates temperatures on Earth

The Universal Solvent H 2 O is a good solvent due to its polarity polar H 2 O molecules surround + & – ions solvents dissolve solutes creating aqueous solutions Saltwater; which is solute? which is solvent?

The universal solvent Many other unique properties of water are due to the hydrogen bonds. For example, ice floats

Questions Many other unique properties of water are due to the hydrogen bonds. For example, ice floats 1.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.

Questions Many other unique properties of water are due to the hydrogen bonds. For example, ice floats 2. Which of the following properties of water is not caused by hydrogen bonding? (A) pH (B) cohesion (C) adhesion (D) surface tension

Questions Many other unique properties of water are due to the hydrogen bonds. For example, ice floats 3. What term describes the sugar in a glass of lemonade? (A) solvent (B) solution (C) solute (D) protein

Questions Many other unique properties of water are due to the hydrogen bonds. For example, ice floats 4. 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.