1. Section 2 Water and Solutions
Chapter 2
Section 2
Water and Solutions
Grade 10 Biology
Fall 2010

2. Bell Ringer http://www.youtube.com/watch?v=orW7CEwcAW8
List some common acids and bases
Why do you think water is such an essential compound?

3. Objectives Analyze the properties of water
Describe how water dissolves substances
Distinguish between acids and bases

4. Water in Living Things 70 percent of your body is made of water
About two-thirds of the molecules in your body are water molecules
Water is the medium in which most cellular events take place

5. Storage of Energy
Water absorbs heat more slowly and retains this energy longer than many other substances do
Many organisms release excess heat through water evaporation
Ex. Sweating
In organisms, the ability to control temp. enables cells to maintain a constant internal temp. when the external temp. changes
Homeostasis

6. Cohesion and Adhesion
Hydrogen bonds between molecules cause the cohesion of liquid water
Cohesion: an attraction between substances of the same kind
Molecules at the surface of water are linked together by hydrogen bonds
This attraction between water molecules causes a condition known as surface tension

7. Cohesion and Adhesion
Water molecules are attracted to similarly polar substances
Adhesion: an attraction between different substances
Adhesion powers process called capillary action

8. Cohesion and Adhesion

9. Aqueous Solutions
Solution: a mixture in which one or more substances are evenly distributed in another substance
Many important substances in the body have been dissolved in blood or other aqueous fluids
Because these substances can dissolve in water, they can more easily move within and between cells

10. Polarity
The polarity of water enables many substances to dissolve in water
Water is a polar substance

11. Polarity Ionic compounds and polar molecules dissolve best in water
Why?
When dissolved in water ions become surrounded by polar water molecules
Ions are attracted to the ends of water molecules with the opposite charge, solution is mixture of water molecules and ions
Similar attraction results with polar molecules
Ions or molecules become evenly distributed in water

12. Polarity Non-polar molecules do not dissolve well in water
Why?
When non-polar substances are placed in water, the water molecules are more attracted to themselves than the non-polar molecules
Result is the non-polar molecules are shoved together

13. Acids Acids: compounds that form hydrogen ions when dissolved in water
When an acid is added to water, the concentration of hydrogen ions in the solution is increased above that of pure water
Hydrogen ion = H+
Acidic compounds have a pH value less than 7

14. Bases
Base: compounds that reduce the concentration of hydrogen ions in a solution
Many bases form hydroxide ions when dissolved in water
Hydroxide ion = OH-
Basic compounds have a pH value greater than 7

15. pH pH scale: based on the concentration of hydrogen ions in solution
All solutions have a pH value between 0 and 14
Each whole number represents a factor of 10
A solution with a pH value of 5, has 10 times as many hydrogen ions as one with a pH value of 6

16. Review T/F Non-polar molecules dissolve very easily in water.
T/F Cohesion and adhesion of water molecules help a plant move water from its roots to its leaves.
T/F When a base is added to water, the concentration of hydrogen ions increases.
T/F A substance has a pH value of 11 therefore it is basic.

17. Answer F: Non-polar molecules dissolve very easily in water.
T: Cohesion and adhesion of water molecules help a plant move water from its roots to its leaves.
F: When a base is added to water, the concentration of hydrogen ions increases.
T: A substance has a pH value of 11 therefore it is basic.