Objectives l PSc –Summarize the characteristics and interactions of acids and bases.

Acids and Bases

Properties of Acids l Acids taste sour. l Lemon juice and vinegar, for example, are both aqueous solutions of acids. l Acids conduct electricity; they are electrolytes.

Properties of Acids l Acids cause certain colored dyes (indicators) to change color. (Litmus paper turns red.)

Properties of Acids l Acids react with metals to form hydrogen gas. (See the bubbles in the test tube to the right.) l This property explains why acids corrode most metals.

Properties of Acids l Acids react with carbonates to form carbon dioxide gas.

Properties of Acids l Acids react with hydroxides (bases) to form water and a salt. l This reaction is referred to as a neutralization reaction.

Household Uses of Acids l Some household uses of acids include: –Cleaning masonry –Adjusting pH in swimming pools –Car batteries –Vinegar –Soft drinks and citrus fruits

Properties of Bases l Taste bitter. l Feel slippery. l Bases also conduct electricity and are therefore electrolytes.

Properties of Bases l Bases cause certain colored dyes (indicators) to change color. (Litmus paper turns blue).

Properties of Bases l Bases react with acids to form water and a salt. l Bases do not commonly react with metals.

Properties of Bases l The reaction of a base with fat or oil results in creating soap.

Household Uses of Bases l Some household uses of bases include: –Cleaning drains –Making mortar, plaster and cement –Fertilizing soil –Cleaning solutions (like ammonia)

Neutralization Reactions l When acid and base solutions are mixed in the right proportions, the positive ions from the base combine with the negative ions from the acid. l A new ionic compound forms and water is one of the products. l This is a neutralization reaction.

The pH scale l The pH scale ranges from 0 to 14. –Acids have a pH less than 7. –A base has a pH greater than 7. –Pure water has a pH equal to 7.

The pH scale l Red and blue litmus paper are pH indicators that test for acids or bases.

pH in the environment l The pH of soil directly affects the availability of nutrients for plants. l For example, blueberry plants grow best in acid soils (pH 4.0 to 5.0).

pH in the environment l The pH of water directly affects aquatic life.

Acids and bases in your body l Many reactions, such as the ones that occur in your body, work best at specific pH values.

pH and blood l The pH of your blood is normally within the range of 7.3–7.5. l Holding your breath causes blood pH to drop. l High blood pH can be caused by hyperventilating.

Arrhenius Definition l Acids will always contain one or more hydrogen ions next to an anion. l The simplest definition is that an acid is a substance that produces hydronium ions when it dissolves in water. l A hydronium ion, H 3 O +, consists of a hydrogen ion attached to a water molecule.

Arrhenius Definitions l A hydronium ion, H 3 O +, is equivalent to H +. l HCl and H 3 PO 4 are acids according to Arrhenius.

Arrhenius Definitions l A base is a substance that produces hydroxide ions, OH –, when it dissolves in water. l Ca(OH) 2 and NaOH are Arrhenius bases. l NH 3, ammonia, could not be an Arrhenius base.

Common Acids l Common acids include: –Hydrochloric acid (also called muriatic acid) = HCl –HCl is found naturally in gastric acid.

Common Acids l Common acids include: –Sulfuric acid = H 2 SO 4 –H 2 SO 4 is used in car batteries.

Common Acids l Common acids include: –Acetic acid = HC 2 H 3 O 2 –HC 2 H 3 O 2 is the main component in vinegar.

Common Acids l Common acids include: –Nitric acid = HNO 3 –The main use of nitric acid is for the production of fertilizers.

Common Acids l Common acids include: –Citric acid = C 6 H 8 O 7 –The dominant use of citric acid is as a flavoring and preservative in food and beverages, especially soft drinks.

Common Bases l Common bases include: –Sodium bicarbonate = NaHCO 3 –Sodium bicarbonate, referred to as "baking soda" is primarily used in cooking (baking).

Common Bases l Common bases include: –Ammonia = NH 3 –Approximately 83% (as of 2004) of ammonia is used as fertilizers either as its salts or as solutions.

Common Bases l Common bases include: –Sodium hydroxide = NaOH –Potassium hydroxide = KOH –Magnesium hydroxide = Mg(OH) 2 –Barium hydroxide = Ba(OH) 2 –Calcium hydroxide = Ca(OH) 2

Acids and Bases Video l Give examples of acids and bases. l How does an electrolyte affect water? l What is the Arrehenius definition of an acid and a base? l Describe the pH scale. l Describe the human digestive process. l How did aspirin come to be used as a remedy?