Water and Solutions 2.2

1. Water and Solutions 2.2 Water and Living Things

2. Water and Solutions 2.2 Water in Living Things • All living things have a percentage of water in their makeup • The human body contains about 72%, or two thirds, of it’s makeup in water.

3. Water and Solutions 2.2 Water in Living Things • Cellsin the body are in large part made up of water. • Waterhelps move nutrients and other substances in and out of your cells.

4. Storage of Energy • Water absorbs heat more slowly and retains this energy longer than many other substances. • Many organism release excess heat through water evaporation. • Humans cool themselves by sweating. • The water vapor lost through evaporation of sweat carries away heat from the body.

5. Storage of Energy • In organisms, this ability to control temperature enables cells to maintain a constant internal temperature when the external temperatures are varying drastically. • This is called homeostasis and is how organisms help regulate their body temperature.

6. Cohesion and Adhesion • The hydrogen bonds between water molecules cause the cohesion of liquid water. • Cohesion is an attraction between substances of the same kind.

7. Cohesion and Adhesion • Because of cohesion, water and other liquids form thin films and drops. • Molecules at the surface of the water link together by hydrogen bonds like a crowd of people linked holding hands.

8. Cohesion and Adhesion • This attraction between water molecules causes a condition know as surface tension • Surface tension prevents the surface of water from stretching or breaking easily.

9. Cohesion and Adhesion • Water molecules are also attracted to many other “similarly polarized” substances. • Adhesion is an attraction between different substances.

10. Cohesion and Adhesion • Adhesionpowers a process called capillary action in which water molecules move upward through the stem of a plant. • The attraction of water to the walls of the tube sucks the water up more strongly than gravity pulls it down.

11. Cohesion and Adhesion • Water moves upward through a plant from roots to leaves through a combination of capillary action, cohesion and other factors. • Putting a paper towel into water is a good demonstration of capillary action as the paper towel draws the water up.

12. Aqueous Solutions • Many substances dissolve in water. • For example, when you add salt to water, the resulting mixture is a saltwater solution. • A solution is a mixture in which one or more substances are evenly distributed in another substance. • When you drop food coloring into water and it changes the color, you have created a solution.

13. Acids and Bases • While the bonds in water molecules are strong, at any time a certain amount of these bonds will break, forming a hydrogen ion (H+) and a hydroxide ion (OH-). Water molecule

14. Acids and Bases • Hydrogen ions (H+) are ions with a positive charge and make water acidic. • We say that acidic water with a positive charge has a positive polarity. Water molecule

15. Acids and Bases • Hydroxide ions (H-) are ions that have a negative charge and make water more base. • We say that water with a negative charge has a negative polarity. Water molecule

16. Acids and Bases • As a result, pure water always has a low amount of hydrogen ions and hydroxide ions in equal numbers =

17. Acids and Bases • Compounds that form hydrogen ions (H+) when dissolved in water are called acids. • When an acid is added to water, the concentration of hydrogen ions (H+)in the solution is increased above that of pure water. (greater than 7.0pH)

18. Acids and Bases • In contrast, compounds that reduce the concentration of hydrogen ions in a solution are called bases. (OH-) • Many bases lower the concentration of hydrogen ions because hydroxide ions react with hydrogen ions to form water molecules.

19. Acids and Bases • A pH scaleis based upon the concentration of hydrogen ions in a solution. • Pure water is balanced at a pH of 7.0 and is neutral pH.

20. Acids and Bases • The more hydrogen ions (+), the more acidic the solution. • An acidic solution has a pH lower than 7.0 • Lemon juice or vinegar are both very acidic.

21. Acids and Bases • The more hydroxide ions a solution has, the less acidic and more base the solution. • A base solution has a pH reading higher than 7.0 (neutral) and is considered more alkaline. • Lye is a compound that is very alkaline.