The Chemistry of Acids and Bases

Objectives Define the following: Acids Bases The pH scale compare/ contrast properties of acids and bases Describe common uses of acids and bases Explain and write equations for the chemical reactions that occur between acids and bases

Acids Acid – a chemical which easily “donates” (loses) a hydrogen ion (H+) when placed in an aqueous solution Examples: Carbonic Acid Hydrochloric Acid Stomach Acid Battery Acid

Properties of Acids Cause foods to taste tart or sour (vinegar – contains acetic acid) React with metals to produce hydrogen gas React with a base to produce an ionic salt and water Found in many citrus foods Form electrolytes when placed into water

Dissociation of an acid in water An acid will dissociate (break apart) into H+ ions and negative ions when placed into water Example: HCl (g) H+ (aq) + Cl- (aq) H2O

When the acid dissociates into H+ ions and negative ions, some of the water molecules will bond with the H+ ions and form a Hydronium ion (H3O+) The strength of Acids are actually measured by the amount of Hydronium ions they form when placed in water

Bases Base – a chemical which easily “accepts” (gains) a hydrogen ion (H+) when placed in an aqueous solution Examples: Potassium Hydroxide Magnesium Hydroxide Ammonia

Properties of Bases Taste bitter Feel slippery Will form electrolytes when placed in aqueous solutions Found in many soaps and household cleaners

Dissociation of a base in water A base will dissociate (break apart) into OH- ions and positive ions when placed into water The OH- ions will then “accept” Hydrogen ions Example: NaOH (s) Na+ (aq) + OH- (aq) H2O

Acid – Base Chemical Reactions A neutralization reaction will occur when an acid and a base are mixed in an aqueous solution: Acid + Base Salt + Water HCl (aq) + NaOH (aq) NaCl (s) + H2O HNO3 (aq) + Mg(OH)2 (aq) Mg(NO3)2 (s) + H2O

The pH Scale Measures the relative strength of acids and bases Range is from 0 – 14 0 = strongest acids 7 = neutral 14 = strongest bases

The pH scale is logarithmic A solution with a pH value of 4 has 10 times as many H+ ions as a solution with a pH value of 5 A solution with a pH value of 3 has 100 times as many H+ ions as a solution with a pH value of 5

What is a buffer? A buffer solution is a solution that will resist extreme changes in pH when mixed with a strong acid or a strong base A buffer is usually a mixture of a weak acid and a weak base

Societal Issue: Acid Rain Acid rain is rain that is acidic (has a pH between 5 and 6.5) Is caused by air pollutants such as Sulfur dioxide and Nitrogen oxides These pollutants react with the atmosphere, causing precipitation to be acidic Societal Issue: Acid Rain

Effects of Acid Rain Run- off from acid precipitation causes lakes and streams to become acidic kills fish, plants, and other aquatic organisms pollutes ground water Destroys trees (forests) Damages statues, buildings, etc.

Summary Acids = donate H+ ions Bases = accept H+ ions Taste tart/ sour, found in many foods Bases = accept H+ ions Found in soaps/ cleaning products Acid + Base = salt + water The pH scale measures the strength of acids and bases