2.  You go to a grocery store to purchase lemons, milk, tomatoes, and soap.  Have you purchased any items that are acidic, neutral, or basic?  An indicator will help determine which category various items fit into.

3. Acids  Acids are compounds that release hydrogen ions (H+) when placed in water. The more hydrogen ions that are released, the greater the acidity of the compound.  Examples of strong acids : Hydrochloric acid, and Sulfuric acid.  Examples of weak acids : Vinegar, and acetylsalicylic (aspirin).

4.  Acids tend to be sour in taste and are readily soluble in water.  It is important for gardeners to know the chemical nature of the soil. They buy fertilizers that supplement soil deficiencies. Acidic soil requires fertilizer containing potash to make it less acidic.  Manufacturers of car batteries use sulfuric acid to provide the reaction required for producing an electrical current.  Stomach acid help breakdown food protein into form that can be absorbed into the blood stream.

5. Bases  Bases are compounds that release hydroxyl ions (OH-) into water.  Bases are slippery to the touch, bitter in taste, and soluble in water.  Bases are important in our lives.  Baking soda makes cakes and bread rise.  Soaps and shampoos are used for cleaning.

6. Indicators  An indicator is a chemical substance, usually obtained from plant material that changes color in the presence of an acid or base.  The most common indicator is called the universal indicator.  It comes as a special bottled solution or paper dipped in this solution (pH paper).  Several other types of acid-base indicators include litmus and red cabbage juice.

7. Indicator Examples  Litmus paper demonstrationdemonstration  Bromothymol blue demonstrationdemonstration  Rainbow Connection demonstrationdemonstration

8.  The universal indicator changes to different colors in different substances. The color is compared to a pH scale and pH number of the substance is determined.

9. The pH Scale  The pH scale is designed to indicate the concentration of hydrogen ions in a solution.  A pH scale ranges from 0 to 14.  Acids fall in a range from 0 to 6, neutral substances are 7, and bases range from 8 to 14.  A pH test paper is dipped into a solution and the color produced is compared with a commercial color scale.  A reddish color indicates a pH of 1, green indicates pH of 7, and blue indicates pH of 14.

10.  Common Substances and their pH: (Note p. 198)  Battery acid pH 0.7  Stomach acid pH 1.0  Lemon Juice pH 2.0  Distilled water pH 7.0  Baking soda pH 8.0  Drain cleaner pH 13.5

11.  A substance with pH 1 is a strong acid whereas a substance with pH 5 is a weak acid.  A substance with pH 8 is a weak base whereas a substance with a pH of 14 is a strong base.

12.  As the pH of a substance increases or decreases, the acid concentration increases or decreases.  Every number on the pH scale represents a difference in concentration by a factor of 10. A pH reading of 4 is 100 times more acidic than a pH of 6. Similarly, a pH of 11 is 1000 times more basic than a pH of 8

13. Neutralization  Strong acids and strong bases are corrosive and can be dangerous if not handled properly.  Should the need arise, a strong acid can be neutralized with a strong base.  The process of neutralization involves mixing an acid with a base to produce salt (ionic compound) and water. Acid + Base  Salt + Water

14.  Antacids, like Alka-Seltzer, are taken for stomach acidity.  When taken, an antacids starts a neutralization reaction.  The acid is converted to a type of salt.