Acids and Bases Chapter 3 Section 2 p Vocabulary: 1. acid 2. indicator 3. base

The pH scale is used to decide if substances are: Neutral = 7: example – pure water Acidic = 6 -0: The lower the number, the higher the acidity, examples: banana (5), vinegar (3), hydrochloric acid (0). Basic = 8 – 14: The higher the number, the more basic the substance, examples: soap (10), ammonia (10.5), drain cleaner (14).

Acids and Their Properties p Acid – any compound that increases the number of hydronium ions when dissolved in water. One property of acids is a sour taste. Acids cause some substances to change color. An acid is any compound that increases the number of hydronium ions, H 3 O +, when dissolved in water. Hydronium ions form when a hydrogen ion, H +, separated from the acid and bonds with a water molecule, H 2 O, to form a hydronium ion H 3 O +. Many acids are corrosive which means they can destroy body tissue or clothing. Many acids are also poisonous.

2. indicator – a compound that can reversibly change color depending on conditions such as pH. A substance that changes color in the presence of an acid or base is an indicator. One commonly used indicator in the lab is litmus. Paper strips containing litmus are available in both red and blue. When an acid is added to blue litmus paper, the color of the litmus changes to red.

Acids react with some metals to produce hydrogen gas. For example, hydrochloric acid reacts with zinc metal to produce hydrogen gas as shown in this picture. When acids are dissolved in water, they may break apart and form ions in the solution. The ions make it possible to conduct an electric current. A car battery is one example of how an acid can be used to produce an electric current. The sulfuric acid in the battery conducts electricity to help start the car’s engine.

Uses of Acids Acids are used in many areas of industry and in homes. Sulfuric acid is the most widely made industrial chemical in the world. It is used to make paper, paint, detergents, and fertilizers. Nitric acid is used to fertilizers, rubber, and plastics. Hydrochloric acid is used in swimming pools to help keep them free from algae. Citric acid and ascorbic acid are found in orange juice.

3. base – any compound that increases the number of hydroxide ions when dissolved in water. Bases and Their Properties p Bases taste bitter Bases have a soapy, slippery feel Bases can be corrosive. Bases are compounds that increase the number of hydroxide ions, OH -, when dissolved in water. For example, sodium hydroxide breaks apart to form sodium ions and hydroxide ions as shown below. NaOH → Na + + OH -

Example of Bases

Bases Change Color in Indicators Like acids, bases change the color of an indicator. Bases change the color of red litmus paper to blue.

Uses of Bases Like acids, bases have many uses. Sodium hydroxide is a base used to make soap and paper. It is also used in oven cleaners and in products that unclog drains. Calcium hydroxide is used to make cement and plaster. Ammonia is found in many household cleaners and is used to make fertilizer. Magnesium hydroxide and aluminum hydroxide are used in antacids to treat heartburn.

Quiz Time Classify each of the following compounds as acidic or basic: 1. soap basic 2. vinegaracidic 3. bleach basic 4. baking soda basic 5. ammonia basic 6. lemonade acidic 7. magnesium hydroxidebasic

8. A base is a substance that A. feels slippery B. tastes sour C. reacts with metals to produce hydrogen gas D. turn blue litmus paper red A 9. Acids are important in A. making antacids B. preparing detergents C. keeping algae out of swimming pools D. manufacturing cement C 10. What happens to red litmus paper when it touches a base? It turns blue.