Essential Chemistry: Water

1. Essential Chemistry: Water By Chris Witzigman Tom Cunningham Gabe Fonseca

2. Truths about Water Water molecules are cohesive and form hydrogen bonds Water molecules are adhesive and form hydrogen bonds with polar surfaces Water is a liquid at normal physiological temperatures Water has a high specific heat Water has a high heat of vaporization Water’s greatest density occurs at 4 degrees Celsius.

3. Situation A • During the winter, air temperatures in the northern United States can remain below 0°C for months; however, the fish and other animals in the lakes survive. • http://www.bbc.co.uk/learningzone/clips/life-in-a-frozen-lake/10467.html • Water has a high specific heat • Keeps the water below the ice layer on top warm

4. Situation B • Many substances- for example salt (NaCL) and sucrose- dissolve quickly in water. • Water is adhesive and forms hydrogen bonds with polar substances • The water creates a hydration shell around Na+ and Cl- atoms thus dissolving them.

5. Situation C • When you pour water into a 25-ml graduated cylinder, a meniscus forms at eh top of the water column. • This is the property of adhesion. • The water is attracted to the glass and so clings to the side of the graduated cylinder and dips in the middle. This creates the meniscus.

6. Situation D • Sweating and the evaporation of sweat from the body surface help reduce a human’s body temperature. • This is water’s heat of vaporization • The water on the surface of your skin heats up first and then evaporates leaving the cool water behind and pulling the hot water away, leaving the surface cooler

7. Situation E • Water drops that fall on a surface tend to form rounded drops or beads. • This is the property of cohesion • The polar water molecules create hydrogen bonds and stick together in beads • This is the property of adhesion • The water is polar and tends to stick to polar surfaces

8. Situation F • Water drops that fall on your car tend to bead or round up more after you polish or wax your car. • This is the property of cohesion • The polar water molecules create hydrogen bonds and stick together in beads • The wax is non polar and so the wax and water repel each other creating more beading

9. Situation G • If you touch the edge of a paper towel too a drop of colored water, the water will move up into (or be absorbed by) the towel. • This is water’s property of capillary action. • Water is attracted to the paper fibers by adhesion and is pulled up through the towel and because water creates hydrogen bonds to itself it pulls more water molecules behind it.