WATER Notes: Ch. 3

WATER Notes: Ch. 3

KEY WORDS/

QUESTIONS

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NOTES

Water’s Unique Properties: / KEY: Water’s ability to “work” the way it does is all based on the way it can form hydrogen bonds with other molecules. This bonding is based on the fact that water is a polar molecule.
*General Characteristics of water:
□Hydrogen bonds are weak and they break and reform OFTEN!
□But since there are SO MANY bonds in water, they lead to some VERY important properties that allow life to thrive on the Earth.

1. Heat Storage: “Hydrogen bonds require considerable heat before they break, minimizing temperature changes.”

*Basically, temperature of a substance is a measurement of how fast the individual molecules are moving. The faster they move, the higher the temperature. Since there are so many bonds in liquid water, it takes a large amount of energy to get the molecules to move fast enough to raise the temperature.
*Water has a high SPECIFIC HEAT: water heats up SLOWLY, holds temperature longer than other substances, and cools down SLOWLY.
So what? Who cares?
□You don’t boil when you set foot outdoors in Arizona! You’re body is ~70% water, and b/c of it’s heat storage, your body is able to maintain a relatively constant internal temperature.
□Temperate Coastal Climates: It’s nice living on the coast! The water tends to cool the surroundings.
□You can swim into the winter months in AZ since the pool doesn’t cool down too fast.

1. Ice Formation: “Water molecules in an ice crystal are spaced far apart.” This makes ice LESS dense than water – unlike most other liquids that, when frozen, are MORE dense.

So what? Who cares?
□Fishies and other water-dwelling creatures! Since water freezes from the top down and not the bottom up, the top layer of ice provides a nice insulated climate for the fishies during the winter months. Otherwise, when the top layer of water froze, it would sink, the process would repeat itself and then we couldn’t fish in the winter!

1. High Heat of Vaporization: “Many hydrogen bonds must be broken for water to evaporate.”

*Like mentioned before, when water molecules vibrate fast enough, they can eventually break off from other water molecules. Since this requires a lot of energy, at these high temps the water that breaks off is now in the form of a gas and has vaporized.
So what? Who cares?
□Every gram of water that evaporates from your skin removes 2,452 joules (units) of heat from your body. This is why sweating cools you off! (Evaporative cooling)

1. Cohesion/Adhesion: “Hydrogen bonds hold molecules of water together and attach them to other surfaces.”

*Define C/A
Things that happen b/c of cohesion and adhesion:
□Capillary Action
□Surface Tension: water has a strong surface due to the force of its hydrogen bonds. (Walking on Water Web Quest)
So what? Who cares?
□Trees, so they can get water to the top branches.
□Your blood is primarily water, and thus can move through your vessels.
□Towels “work” when you get out of the shower!
□Water proofing substances!

1. Water as a Solvent: “Water molecules are attracted to ions and polar compounds.”

*Water molecules in a solution always tend to form the maximum number of hydrogen bonds possible. “Like dissolves like.” Since water is a polar molecule, it “likes” to dissolve things that are also polar.
*Key Vocabulary:
□Hydrophilic: aka polar molecules or water-loving molecules. Water molecules surround these molecules and break it apart. These are called “water soluble”.
□Hydrophobic: aka non-polar molecules or water-fearing molecules. These molecules cannot be broken down by water.
□Solvent: substances that dissolve other substances. Water is an example.
□Solute: molecules that can be dissolved.
So what?Who cares?
□You don’t want to walk around as a big slushy mess! Your cells that make up your body have hydrophobic components.
□Lemonade powder can dissolve in water!
□Your blood can carry molecules around the body much easier since they are not all bulky!
SUMMARY