1. Unit 2: All Biology is Chemistry Lesson 3: Water & Solutions

2. Drill 19 October 2009 K-W-L  With a partner, complete the first two columns of the chart: What do I KNOW about water What do I WANT to know about water What have I LEARNED about water

3. Objectives At the conclusion of this lesson students will be able to: 1. describe the structure of a water molecule 2. explain what is meant by a molecule’s polarity 3. explain why hydrogen bonds form between water molecules 4. identify common properties of water that result from hydrogen bonding 5. identify the difference between solutes and solvents in solutions 6. differentiate between acids and bases 7. understand how to read and interpret the pH scale 8. define a buffer and explain their role in living systems

4. The Structure of Water  Composed of two hydrogen atoms covalently bonded to an oxygen atom. Hydrogen Oxygen

5. Polarity  However, oxygen and hydrogen do not share electrons equally. As a result… As a result… Oxygen atom has a partial negative charge ( δ -)Oxygen atom has a partial negative charge ( δ -) Hydrogen atoms have partial positive charges ( δ +)Hydrogen atoms have partial positive charges ( δ +) Total charge of the water molecule is still neutralTotal charge of the water molecule is still neutral 1 p Oxygen 8 p 8 n Oxygen 8 p 8 n δ-δ-δ-δ- δ+δ+δ+δ+ δ+δ+δ+δ+ Obj. 1 Obj. 1 Space filling model of a water molecule

6. Hydrogen Bonding  Water molecules have an uneven distribution of charge Positively charged region ( δ+ ) of one water molecule is attracted to the negatively charged region ( δ- ) of a nearby water molecule. Positively charged region ( δ+ ) of one water molecule is attracted to the negatively charged region ( δ- ) of a nearby water molecule. This attraction is called a hydrogen bond. This attraction is called a hydrogen bond. H H H H O O δ-δ-δ-δ- δ-δ-δ-δ- δ+δ+δ+δ+ δ+δ+δ+δ+ δ+δ+δ+δ+ δ+δ+δ+δ+ H H H H O O δ-δ-δ-δ- δ-δ-δ-δ- δ+δ+δ+δ+ δ+δ+δ+δ+ δ+δ+δ+δ+ δ+δ+δ+δ+

7. Hydrogen Bonds  Weak forces of attraction  Form, break, and reform frequently  Number of hydrogen bonds in water depends on its state (solid, liquid, or gas)

8. Significance of Hydrogen Bonds  Account for the unique properties of water Cohesion Cohesion Surface tension Surface tension Adhesion Adhesion Ability to absorb a relatively large amount of heat energy Ability to absorb a relatively large amount of heat energy Ability to cool surfaces through evaporation Ability to cool surfaces through evaporation Solid state is less dense than its liquid state Solid state is less dense than its liquid state Ability to dissolve many substances Ability to dissolve many substances Obj. 2 Obj. 2

9. Cohesion  Cohesion - an attractive force that holds molecules of a single substance together

10. Surface tension  Tendency of water molecules on the edges of a water droplet to attract inward toward other water molecules thus producing a “skin”

11. Adhesion  Adhesion – attractive force between two particles of different substances

12. Temperature Moderation  Temperature is a measure of heat which is a form of energy Water can absorb large amounts of energy as heat for its molecular size Water can absorb large amounts of energy as heat for its molecular size Water has the highest specific heat of any common substance. Water has the highest specific heat of any common substance. Specific heat is the heat required to raise the temperature of one gram of a substance one degree Celsius.

13. Effects of a High Specific Heat  Water can absorb/release a large quantity of heat without a large change in temperature Moderates coastal climatesModerates coastal climates Reduces dramatic day-night temperature fluctuationsReduces dramatic day-night temperature fluctuations

14. Evaporative Cooling  As water evaporates, the surface of the water that remains behind cools.  Principle behind sweating to maintain body temperature in land animals

15. Density of Ice  Angle of hydrogen bonds causes ice crystals to have lots of open space  Open space leads to low density  As a result, ice floats!  Ponds & lakes freeze from top to bottom.  Ice insulates deeper water from colder air. Ice crystal Liquid water

16. Glossary  adhesion – an attractive force between two particles of different substances  cohesion – an attractive force that holds molecules of a single substance together  hydrogen bond – force of attraction between a hydrogen molecule with a partial positive charge and another atom or molecule with a partial or full negative charge  polar compound – a compound with an uneven distribution of charge within the molecule

17. Work Cited  "Graduated cylinders." 10 mL graduated cylinder. 1995-1995. NT Curriculum Project, UW- Madison. 19 Oct 2006.  Lower, Stephen. "H 2 O: a gentle introduction to the structure of water." 16 May 2005. Dept of Chemistry, Simon Fraser University. 19 Oct 2006.  Microsoft Corporation, "Hydrogen Bonding in Water." MSN Encarta. 19 Oct 2006.  Nave, R. "Water." Hyperphysics Chemistry. 19 Oct 2006.  Saloutos, Peter. "Surface Tension in Water Droplets." MSN Encarta. 19 Oct 2006.  "Specific Heat." 1999. 19 Oct 2006.  "Sunset Island Wedding." Miami Skyline. 31 Aug 2006. 19 Oct 2006.  “Surface tension” Molecules. Retrieved on 19 Oct. 2006 from.