Section 16.1 Properties of Acids and Bases 1. To learn about two models of acids and bases 2. To...

Section 16.1

Properties of Acids and Bases

1. To learn about two models of acids and bases

2. To understand the relationship of conjugate acid-base pairs

3. To understand the concept of acid strength

4. To understand the relationship between acid strength and the strength of the conjugate base

5. To learn about the ionization of water

Objectives

Section 16.1


A. Acids and Bases

• Acid – produces hydrogen ions in aqueous solution • Base – produces hydroxide ions in aqueous solution

The Arrhenius Model

Section 16.1


A. Acids and Bases

• Acid – proton donor • Base – proton acceptor • The general reaction for an acid dissolving in water is

The Bronsted-Lowry Model

Section 16.1


A. Acids and Bases


• Conjugate acid-base pair

Section 16.1


A. Acids and Bases


• Water acts as a base accepting a proton from the acid.

• Forms hydronium ion (H3O+)

Section 16.1


B. Acid Strength

• Strong acid – completely ionized or completely dissociated

Section 16.1


B. Acid Strength

• Weak acid – most of the acid molecules remain intact

Section 16.1


B. Acid Strength

• A strong acid contains a relatively weak conjugate base.

Section 16.1


B. Acid Strength

• Common strong acids are

– Sulfuric acid, H2SO4

– Hydrochloric acid, HCl

– Nitric acid, HNO3

– Perchloric acid, HClO4

Section 16.1


B. Acid Strength

• Oxyacid – acidic proton is attached to an oxygen atom

– Typically a weak acid

• Organic acid – have a carbon atom backbone and commonly contain the carboxyl group

Section 16.1


B. Acid Strength

Section 16.1


C. Water as an Acid and a Base

• Water is amphoteric – it can behave as either an acid or as a base

• Ionization of water

– Concentration of hydronium and hydroxide are equal

Section 16.1



– Product of [H3O+] and [OH] is always constant.

Section 16.1



Section 16.2

Determining the Acidity of a Solution

1. To understand pH and pOH

2. To learn to find pH and pOH for various solutions

3. To use a calculator to find pH

4. To learn methods for measuring pH of a solution

5. To learn to calculate the pH of strong acids

Objectives

Section 16.2


A. The pH Scale

• The “p scale” is used to express small numbers.• pH = log [H+]

Section 16.2


A. The pH Scale

Section 16.2


A. The pH Scale

• Because the pH scale is a log scale based on 10, the pH changes by 1 for every power of 10 change in the [H+].

Section 16.2


A. The pH Scale

Section 16.2


A. The pH Scale

• pOH scale

pOH = log [OH]

• pH + pOH = 14.00

Section 16.2


A. The pH Scale

Section 16.2


B. Measuring pH

• Indicators – substances that exhibit different colors in acidic and basic solutions

– In an acid solution the indicator will be in the HIn form. – In a basic solution the indicator will be in the In form.

Section 16.2


B. Measuring pH

• Other methods

– Indicator paper – pH meter

Section 16.2


C. Calculating the pH of Strong Acid Solutions

• Determine the [H+]. • pH = log[H+]

Section 16.3

Titrations and Buffers

1. To learn about acid-base titrations

2. To understand the general characteristics of buffered solutions

Objectives

Section 16.3


A. Acid-Base Titrations

• Titration – delivering a measured volume of a solution of known concentration into the solution being analyzed

• Titrant – a standard solution • Buret – device used for accurate measurement of the

delivery of a liquid • Stoichiometric point (equivalence point) – when just

enough titrant has been added to react with all of the solution being analyzed

Section 16.3


A. Acid-Base Titrations

• Titration curve (pH curve) – plot of the data (pH vs volume) for a titration

Section 16.3


B. Buffered Solutions

• Buffered solution – resists a change in its pH when either and acid or a base has been added– Presence of a weak acid and its conjugate base

buffers the solution

Section 16.3


B. Buffered Solutions

Section 16.1 Properties of Acids and Bases 1. To learn about two models of acids and bases 2. To...

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