1. Chapter 2 Section 2 Properties of Water
Objectives:
Explain why water molecules are polar.
Differentiate between solutions and suspensions
Explain what acidic solutions and basic solutions are.

2. Vocabulary
cohesion: attraction between molecules of the same substance
adhesion: attraction between molecules of different substances
mixture: material composed of two or more elements or compounds that are physically mixed together but not chemically combined

3. Vocabulary
solution: mixture of two or more substances in which the molecules of the substances are evenly distributed
solute: substance that is dissolved in a solvent to make a solution
solvent: substance in which a solute is dissolved to form a solution

4. Vocabulary suspension: mixture of water and nondissolved materials
pH scale: measurement system used to indicate the concentration of hydrogen ions (H+) in solution
acid: compound that forms hydrogen ions (H+) in solution

5. Vocabulary
base: compound that produces hydroxide ions (OH-) in solution
buffer: weak acid or base that can react with strong acids or bases to help prevent sharp, sudden changes in pH

6. The Water Molecule
A water molecule (H2O) is neutral. The positive charges on its 10 protons balance out the negative charges on its 10 electrons.

7. The Water Molecule: Polarity
The water molecule has a bent shape, the oxygen atom is on one end of the molecule and the hydrogen atoms are on the other. As a result, the oxygen molecule has a slight negative charge and the hydrogen end of the molecule has a slight positive charge.

8. The Water Molecule: Polarity
A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms.

9. The Water Molecule: Hydrogen Bonds
The attraction between the hydrogen atom on one water molecule and the oxygen atom on another water molecule is an example of a hydrogen bond. Hydrogen bonds are not as strong as covalent or ionic bonds, but water’s ability to form multiple hydrogen bonds is responsible for many of its special properties.

11. The Water Molecule: Hydrogen Bonds
A single water molecule may be involved in as many as four hydrogen bonds at the same time. Because of hydrogen bonding, water is extremely cohesive.

12. The Water Molecule: Hydrogen Bonds
Adhesion between water and glass causes a dip in the center of water in a graduated cylinder and water to rise in a narrow tube against the force of gravity.

13. Solutions and Suspensions
Examples of mixtures:
salt and pepper
sugar and sand
Earth’s atmosphere

14. Solutions and Suspensions
All the components of a solution are evenly distributed throughout the solution.
ex. table salt and water
table salt is the solute
water is the solvent
salty water is the solution

15. Solutions and Suspensions
Some materials do not dissolve when placed in water but separate into pieces so small that they do not settle out.
The movement of water molecules keeps the small particles suspended.

16. Acids, Bases, and pH The pH scale: ranges from 0 to 14
pH of 7 = H+ ions and OH- ions are equal
(ex. pure water)
pH below 7 = acidic
more H+ ions than OH- ions
pH above 7 = basic
more OH- ions than H+ ions
Each step on the pH scale represents a factor of 10.

18. Acids, Bases, and pH Acids:
Acidic solutions contain higher concentrations of H+ ions than pure water and have pH values below 7.

19. Acids, Bases, and pH Bases:
Basic, or alkaline, solutions contain lower concentrations of H+ ions than pure water and have pH values above 7.

20. Acids, Bases, and pH Buffers:
Controlling pH is important for maintaining homeostasis. One of the ways that the body controls pH is through dissolved compounds called buffers.