The Chemistry of Life

1. The Chemistry of Life Properties of Water

2. Water Molecules • Havean Equal number of p+ and e- but… • Charges aren’t evenly distributed so… • What does that mean?

3. Water Molecules • Have Polarity • A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms. (-) (+)

4. Hydrogen Bonds • Polar water molecules act like magnets and attract each other • Hydrogen Bonds • The attraction of the Hydrogen end (+) of one molecule for the Oxygen end (-) of another water molecule. • They are strong bonds that form between molecules (CO2, H2O, …)

5. Hydrogen Bonds

6. Properties related to Hydrogen Bonds • High Specific Heat • Cohesion, Surface tension • Adhesion

7. High Specific Heat • This means water resists changes in temperature – water must absorb more energy to increase in temperature • How is this useful in cells? Remember - Homeostasis

8. Cohesion • The attraction between molecules of the same substance (e.g. water). • H2O attracting other H2O molecules • Allows some insects and spiders to walk on water – surface tension • Basilisk lizard

9. Adhesion & Capillarity • Adhesion - Attraction between H2O molecules and different molecules • Cohesion & adhesion produceCapillary action(upward movement against gravity of water through small tubes) Question: How do plants make use of Capillary action?

10. Penny Lab

11. Density of Water • Water is one of few substances that are less dense as a solid – Demo ice floats • As it freezes it becomes locked into a crystalline structure with molecules farther apart – have 6 students visually represent more space between water molecules making water less dense (about 10%) • Why is this property an important factor in the fitness of the environment? Think frozen lake

12. Many Compounds Dissolve in Water • When compounds dissolve in water a solution is formed. • The solvent is the substance that dissolves another substance • The solute is the substance that dissolves into the solvent • Water is called “the solvent of life” – why?

13. Substances can be ….. • Hydrophilic – an affinity for water Examples: • Hydrophobic – no affinity for water Examples:

14. Properties of Water • Polarity, Cohesion/ Adhesion • High Specific Heat • Less Dense as a Solid • Universal Solvent Changes occur when substances are dissolved in water….

15. Acids and Bases Some compounds form acids when they dissolve in water Some compounds form bases when they dissolve in water Greater concentration of OH¯ ions Lower concentration of H+ ions • Greater concentration of H+ ions • Lower concentration of OH¯ ions

16. pH Scale

17. The pH Scale • Indicates the concentration of H+ ions • Ranges from 0 – 14 • pH of 7 is neutral • pH 0 up to 7 acid … H+ • pH above 7 to 14 base… OH- • Each pH unit represents a factor of 10X change in concentration How much stronger is a pH3 than a pH of 5?

18. Acids • Strong Acid = pH 1-3 • High in H+ions • Lower number of OH- ions

19. Bases • Strong Base = pH 11 – 14 • High in OH-ions • Lower in number of H+ ions

20. Buffers • Weak acids or bases that react with strong acids or bases • Made by the body • Prevent sharp, sudden changes in pH (keep pH neutral) Maintains Homeostasis

21. pH Lab • Vinegar • OJ • Cola • Milk • Distilled Water • Soapy Water • Alka-seltzer • Fertilizer • Lime • Cleaning Fluid

22. Lab Questions • What is pH? • Temperature and pH are important in Biology. These two abiotic factors are for homeostasis in cells. How do cells maintain pH?

23. Review Water Lizard running on water • Hydrogen Bonds • Properties of Water Polarity, High Specific Heat, Adhesion/ Cohesion, Density, Universal solvent • pH

24. Word Bank Polar Cohesion Solvent Acids Hydrogen Adhesion Solute Bases Buffer Homeostasis Density Predator pH High Specific Heat Oxygen Temperature Hydrophilic Hydrophobic Covalent bonds Ionic bonds Solution Capillary action