INTRODUCTION: Acids and bases are a significant class of chemicals whose chemistry pervades our human existence. Sulfuric acid is the most produced and utilized chemical in the US. Hydrofluoric acid is used to etch silicon computer chips, and the base, lime (CaO), is a major component of concrete and mortar. Several organic acids are common vitamins, e.g. vitamin C, folic acid and pantothenic acid. Acids and bases have the ability to turn vegetable dyes different colors. Such pH sensitive dyes are used as acid/base indicators. When acids and bases react in stoichiometrically equivalent amounts, they neutralize one another; they can negate each other’s properties. So in some sense acids and bases are opposite of one another. This type of reaction is called the neutralization reaction. When such a reaction is carefully monitored by an indicator, and the quantities measured, a titration is performed. The products of an acid base reaction are always water and a salt. This salt produced may have acidic or basic properties of its own depending of the acid and base that reacted to form it. Finally, in keeping with a biological focus, our blood has a carefully controlled acid / base balance. This balance is maintained by a buffer. This buffer system carefully maintains the right pH of our blood. Acids and bases are essential not only in our bodies but also in industry as well. In this unit we will examine the properties of acids and bases, and how their chemistry is described and measured. We will learn about titration experiments and buffer systems and their application to our lives.
OBJECTIVES: As you study this unit, you should be able to do the following:
Identify common physical and chemical properties of acids and bases. (19.1)
State the Bronsted-Lowry definition of acids and bases, and identify conjugate acid-base pairs in acid-base reactions using the Bronsted-Lowry theory. (19.1)
Describe the auto-ionization equilibrium of water with a chemical equation and a Keq expression. (19.2)
Describe the pH scale. (19.2)
Inter-convert between the pH of a solution and the hydronium-ion or hydroxide-ion concentration. (19.2)
Explain how equilibrium constants are related to the dissociation constants of acids and bases. (19.3)
Describe an acid-base titration, including how indicators are used and how they are chosen. Point out key elements of various titration curves. (19.4)
Explain what dissociation constants indicate about an acid’s or base’s strength. (19.3)
Demonstrate how certain salts can exhibit acidic or basic properties. (19.5)
Identify a buffer, and with chemical equations explain how buffers work. (19.5)
LEARNING ACTIVITIES:
To learn about objectives 1-10:
[ READ Chapter 19, pp. 587-623.
[ WRITE "ChemActivity 42: Acids and Bases" (handout)
[ WRITE GIA 10-1: Acid Base Reactions
[ READ, PERFORM and WRITE-UP experiment "Exploring Acid-Base Properties of Ammonium Salts."
[ WRITE GIA 10-2: Acid / Base Equilibrium and Ka.
[ READ, PERFORM and WRITE-UP experiment "Investigating Benzoic Acid."
[ WRITE GIA 10-3: pH and Logarithms.
[ WRITE "ChemActivity 43: Strong and Weak Acids" (Handout)
[ READ, PERFORM and WRITE-UP experiment "Turn It Pink."
[ WRITE GIA 10-4: Ka and Buffers.
[ WRITE answers to end of chapter questions: 48, 49, 51-59, 61, 66-69, 73-76, 80, 82 found on pp. 625-626.
[For May 2008 quiz 19B: Answer the following end-of-chapter questions for chapter 19: 48, 49, 54, 58, 59, 61, 65, 67, 69, 73, 76, 80, 82. These can be found on pages 625 and 626. These are due the day of the quiz.]
To make sure you understand the objectives for this unit:
[ ASK me, the teacher, any lingering QUESTIONS
