1. Lesson Overview Lesson Overview Properties of Water Unit 2 - Biochemistry Properties of Water

2. Lesson Overview Lesson Overview Properties of Water THINK ABOUT IT Looking back at Earth from space, an astronaut called it “the blue planet,” referring to the oceans of water that cover nearly three fourths of Earth’s surface. The very presence of liquid water tells a scientist that life may also be present on such a planet. Why should life itself be connected so strongly to something so ordinary that we often take it for granted?

3. Lesson Overview Lesson Overview Properties of Water A. Polarity A water molecule is made of two atoms of H and one atom of O covalently bonded together. The oxygen end has a slight negative charge and the hydrogen end of has a slight positive charge.

4. Lesson Overview Lesson Overview Properties of Water Polarity (cont.) A molecule in which the charges are uneven is said to be “polar,” similar to poles of a magnet.

5. Lesson Overview Lesson Overview Properties of Water B. Hydrogen Bonding Because of their partial + and - charges, polar molecules can attract to each other. Weak attraction between a H atom on one water molecule and the O atom on another is called a hydrogen bond.

6. Lesson Overview Lesson Overview Properties of Water Hydrogen Bonding Multiple hydrogen bonds account for many of water’s special properties!

7. Lesson Overview Lesson Overview Properties of Water C. Cohesion Cohesion is an attraction between molecules of the same substance.

8. Lesson Overview Lesson Overview Properties of Water Cohesion Causes water molecules to be drawn together, which is why drops of water form “beads” on a smooth surface. Also produces surface tension, explaining why some insects can walk on water!

9. Lesson Overview Lesson Overview Properties of Water D. Adhesion Adhesion is an attraction between molecules of different substances. Surface of water in a graduated cylinder dips slightly in center, forming a curve called a meniscus, because of adhesion between water and glass molecules.

10. Lesson Overview Lesson Overview Properties of Water Adhesion Also causes water to rise in a narrow tube against the force of gravity. This effect is called capillary action. This draws water from the roots of a plant and up into its stems and leaves. NASA water video clip - Let's check it out!

11. Lesson Overview Lesson Overview Properties of Water E. High Heat Capacity It takes a large amount of heat energy to cause water molecules to move faster and raise its temperature. Oceans and lakes can absorb large amounts of heat with only small changes in temperature. Why would this be important? Protects organisms living from drastic changes in temperature.

12. Lesson Overview Lesson Overview Properties of Water F. Universal Solvent Water is capable of dissolving a variety of different substances Water in our bodies can dissolve the food we eat & transport necessary chemicals throughout our body

13. Lesson Overview Lesson Overview Properties of Water EX: table salt (NaCl) dissolving in water Ions are formed, creating a type of mixture called a solution.

14. Lesson Overview Lesson Overview Properties of Water Solubility Compare water and oil in beaker when pinch of salt is added Which is better solvent, polar water or non- polar oil?

15. Lesson Overview Lesson Overview Properties of Water G. Acids, Bases, and pH Water molecules sometimes split apart to form hydrogen ions and hydroxide ions. Because the number of H+ produced is equal to the number of OH- produced, pure water is neutral.

16. Lesson Overview Lesson Overview Properties of Water H. The pH Scale Chemists devised a measurement system called the pH scale to indicate the concentration of H + ions in solution. The pH scale ranges from 0 to 14. At a pH of 7, the concentration of H + ions and OH – ions is equal. Pure water has a pH of 7.

17. Lesson Overview Lesson Overview Properties of Water The pH Scale Solutions with a pH below 7 are called acidic because they have more H + ions. The lower the pH, the greater the acidity. Solutions with a pH above 7 are called basic because they have less H + ions. The higher the pH, the more basic.

18. Lesson Overview Lesson Overview Properties of Water I. Buffers The pH of the fluids within most human cells must generally be kept between 6.5 and 7.5 in order to maintain homeostasis. One way that organisms control pH is through buffers, which are weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes in pH.