Water – Chapter 11

Properties of Water Polar molecule Cohesion and adhesion High specific heat Density – greatest at 4 o C Universal solvent of life

Polarity of Water In a water molecule two hydrogen atoms form bonds with an oxygen atom. This gives water a positive side and a negative side like a magnet. –the part around oxygen has a partial negative charge. –The part near the two hydrogen atoms has a partial positive charge.

Polarity of Water We say water is a POLAR molecule because it has a positive pole and a negative pole (like north and south poles)

Cool Properties of Water

–Water’s “polar-ity” makes it sticky

Living things Depend on Water’s “stickiness” In plants, water can move against gravity. It helps move chemicals around inside your body.

Water has a high “Surface tension” –Water behaves as if covered by an invisible film. –Some animals can stand, walk, or run on water without breaking the surface!

Cool Properties of Water –Water’s “polar-ity” makes it sticky –Resists changes in temperature So, water can absorb or release lots of heat with only a little change in its own temperature. It acts like a heat battery.

Degrees Celsius at Sea Level 100 o CWater boils 37 o CHuman body temperature 23 o CRoom temperature 0oC0oCWater freezes What does altitude have to do with boiling & freezing? The higher you are, the lower the air pressure is, so water molecules want to fly around.

Cool Properties of Water –Water’s “polar-ity” makes it sticky –Resists changes in temperature –Takes a lot of heat to turn it into a vapor

Cool Properties of Water –Water’s “polar-ity” makes it sticky –Resists changes in temperature –Takes a lot of heat to turn it into a vapor –Expands when it freezes So, ice floats!

Cool Properties of Water –Water’s “polar-ity” makes it sticky –Resists changes in temperature –Takes a lot of heat to turn it into a vapor –Expands when it freezes –Lots of things can dissolve in it

Chapter 11, page % of Earth’s surface is covered by water.

Chapter 11, page % of Earth’s surface is covered by water. 2.97% of Earth’s water is salt water.

Chapter 11, page % of Earth’s surface is covered by water. 2.97% of Earth’s water is salt water. 3.70% of freshwater is frozen.

Chapter 11, page % of Earth’s surface is covered by water. 2.97% of Earth’s water is salt water. 3.70% of freshwater is frozen. 4.Your body is 2/3 water.

Page 365

The Water Cycle: page 365

1.Evaporation: Heat causes water molecules to spread out into a vapor. When salt water evaporates, the salt is left behind (making fresh water vapor).

The Water Cycle: page Evaporation: Heat causes water molecules to spread out into a vapor. 2.Condensation: As air cools, water molecules slow down and stick together.

The Water Cycle: page Evaporation: Heat causes water molecules to spread out into a vapor. 2.Condensation: As air cools, water molecules slow down and stick together. 3.Precipitation: When enough water molecules stick together, they fall to the ground

The Water Cycle: page Evaporation: Heat causes water molecules to spread out into a vapor. 2.Condensation: As air cools, water molecules slow down and stick together. 3.Precipitation: When enough water molecules stick together, they fall to the ground

Three-fourths of the earth is covered by water. The water serves as a large heat sink responsible for: 1.Prevention of temperature fluctuations that are outside the range suitable for life. 2.Coastal areas having a mild climate 3.A stable marine environment Specific Heat is the amount of heat that must be absorbed or lost for one gram of a substance to change its temperature by 1 o C.

Evaporative Cooling The cooling of a surface occurs when the liquid evaporates This is responsible for: –Moderating earth’s climate –Stabilizes temperature in aquatic ecosystems –Preventing organisms from overheating

Density of Water Most dense at 4 o C Contracts until 4 o C Expands from 4 o C to 0 o C The density of water: 1.Prevents water from freezing from the bottom up. 2.Ice forms on the surface first—the freezing of the water releases heat to the water below creating insulation. 3.Makes transition between season less abrupt.

–When water reaches 0 o C, water becomes locked into a crystalline lattice with each molecule bonded to to the maximum of four partners. –As ice starts to melt, some of the hydrogen bonds break and some water molecules can slip closer together than they can while in the ice state. –Ice is about 10% less dense than water at 4 o C. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 3.5

Solvent for Life Many chemicals can dissolve in water. Chemistry of life happens in water.