Class Starter

1. Class Starter Write what you think an acid and a base are and why. Guess if the following substances are acids or bases, and give a reason for your choice: lemon juice water household ammonia blood soda pop milk antacid shampoo Can you find any similar characteristics between acids and bases? • Acids are usually sour and corrosive, and bases are usually bitter. Acid Neutral Base Neutral Acid Neutral Base Base

2. Objectives • What makes water a unique substance? • How does the presence of substances dissolved in water affect the properties of water?

3. Section 3.2: Water and Solutions

4. Properties of Water • Water has many unique properties that make it an important substance for life. • Most of the unique properties of water result because water molecules form hydrogen bonds with each other. • When water freezes, the crystal structure formed due to hydrogen bonding makes ice less dense than liquid water.

5. Properties of Water • Water can absorb a large amount of heat without changing temperature. This property can help organisms maintain a constant internal temperature. Cohesion • The attraction of particles of the same substance, such as water. • keeps water from evaporating easily; thus, water is a liquid at ordinary temperatures. Adhesion • The attraction between particles of different substances. • Water molecules also stick to other polar molecules.

6. COHESION ADHESION Water compounds attract To glass molecules And form a meniscus Water compounds attract To one another- causes water to “bead”

7. Solutions • A solution is a mixture in which ions or molecules of one or more substances are evenly distributed in another substance. • Many substances are transported throughout living things as solutions of water. Dissolved substances can move more easily within and between cells. • Water dissolves many ionic and polar substances but does not dissolve nonpolar substances.

8. Checkpoint • What type of bond forms between water molecules? • What is the difference between cohesion and adhesion? • What is a solution? • What type of substances can water dissolve? • What type of substances can’t water dissolve?

9. Class Starter • What makes sour candy taste so sour?

10. Answer • Sour candy is coated with a mixture of sugar, citric acid and tartaric acid. • Acids produce a sour taste.

11. Solutions Acids and Bases • Some water molecules break apart to form hydrogen and hydroxide ions. • In pure water, hydrogen and hydroxide ions are present in equal numbers. • Acids and bases are compounds that change the balance of these ions.

13. Acids and Bases Water can react to form individual ions: H2O H+ + OH- • In pure water this occurs naturally but the amount of H+ is always = to the amount of OH- so water remains neutral

14. Solutions Acids and Bases Acids • are compounds that form extra hydrogen ions when dissolved in water. Bases • are compounds that form extra hydroxide ions when dissolved in water. • When acids and bases are mixed, the extra hydrogen and hydroxide ions react to form water.

15. Solutions pH and Buffers • pH is a measure of how acidic or basic a solution is. • Each one-point increase in pH represents a 10-fold decrease in hydronium ion concentration. • Pure water has a pH of 7. • Acidic solutions have a pH below 7 • Basic solutions have a pH above 7.

16. pH Scale

18. Solutions pH and Buffers • The pH of solutions in living things must be stable. • For a stable pH to be maintained, the solutions in living things contain buffers. Buffer • a substance that reacts to prevent pH changes in a solution.

19. Checkpoint • What is the difference between an acid and a base? • What is the pH scale? • What is the range of pH for: • Acid • Base • Neutral • What is the function of a buffer?

20. Summary • The hydrogen bonding between water molecules explains many of the unique properties that make water an important substance for life. • Acids and bases change the concentration of hydronium ions in aqueous solutions. The pH of solutions in living things must be stable.