Acids, Bases and Salts

Chapter 19

Bracken Cave, near San Antonio, Texas, is home to twenty to forty million bats. Visitors to the cave must protect themselves from the dangerous levels of ammonia in the cave. Ammonia is a byproduct of the bats’ urine. You will learn why ammonia is considered a base.

Acid-Base Theories19.1

Taste sour Are electrolytes Neutralize bases to form water and a salt React with some metals to produce hydrogen gas Change acid-base indicator colors

Properties of Acids19.1

Common Acids19.1

Citrus fruits contain citric acid. Tea contains tannic acid.

Common Acids19.1

Taste bitter Feel slippery Are electrolytes Neutralize acids to produce water and a salt Change acid-base indicator colors

Properties of Bases19.1

Common Bases19.1

Antacids use bases to neutralize excess stomach acid. The base calcium hydroxide is a component of mortar.

Common Bases19.1

Arrhenius said that acids yield hydrogen ions (H+) as the only positive ion in solution.

HCl H+ + Cl-

H2SO4

H3PO4

Note: Arrhenius acid formulas start with H

Arrhenius Theory19.1

Arrhenius said that bases yield hydroxide ions (OH–) as the only negative ion in solution.

NaOH Na+ + OH-

Ca(OH)2

Note: Arrhenius bases end in -OH

Arrhenius Bases19.1

◦ Which of the following acids and bases do not fit the definition of an Arrhenius acid or base?

NH3

Ca(OH)2

HCl H2SO4

CO2

NaOH

Arrhenius acids and bases

◦ The Brønsted-Lowry theory defines an acid as a proton donor, and a base as a proton acceptor.

The Regents refers to this theory as “the other theory”

Brønsted-Lowry Theory19.1

◦ Ammonia is a Base

Brønsted-Lowry Acids and Bases

19.1

Identify the Bronsted-Lowry acids and bases in the following equations:

NH3 + H2O NH4+ + OH-

HCl + H2O H3O+ + Cl-

A Lewis acid is a substance that can accept a pair of electrons to form a covalent bond.

A Lewis base is a substance that can donate a pair of electrons to form a covalent bond.

Lewis Theory19.1

Lewis Acids and Bases19.1

To test a diagnosis of diabetic coma, a doctor orders several tests, including the acidity of the patient’s blood. Results from this test will be expressed in units of pH. You will learn how the pH scale is used to indicate the acidity of a solution and why the pH scale is used.

Hydrogen Ions and Acidity19.2

◦ The reaction in which water molecules produce ions is called the self-ionization of water.

Hydrogen Ions from Water19.2

In the self-ionization of water, a proton (hydrogen ion) transfers from one water molecule to another water molecule.

Hydrogen Ions from Water19.2

The product of the concentrations of the hydrogen ions and hydroxide ions in water is called the ion-product constant for water (Kw) and equals 10-14

Ion Product Constant for Water

19.2

Any aqueous solution in which [H+] and [OH-] are equal is neutral.

An acidic solution is one in which [H+] is greater than [OH-].

Ion Product Constant for Water

19.2

Unrefined hydrochloric acid, commonly called muriatic acid, is used to clean stone buildings and swimming pools.

Ion Product Constant for Water

19.2

A basic solution is one in which [H+] is less than [OH]. Basic solutions are also known as alkaline solutions.

Ion Product Constant for Water

19.2

Sodium hydroxide, or lye, is commonly used as a drain cleaner.

Ion Product Constant for Water

19.2

◦ The pH of a solution is the negative logarithm of the hydrogen-ion concentration.

The pH Concept19.2

The pH Concept19.2

A solution with a [H+] greater than 1 10–7 M has a pH less than 7.0 and is acidic.

A solution with a [H+] = [OH-] is neutral and has a pH of 7.

A solution with a [H+] less than 1 10–7 M has a pH greater than 7 and is basic.

The pH Concept19.2

19.2

The pH Concept

The pH Concept19.2

◦ An indicator is a valuable tool for measuring pH because its acid form and base form have different colors in solution. Acid-Base Indicators shift at different pH’s resulting

in color changes.

Measuring pH19.2

Measuring pH19.2

Phenolphthalein changes from colorless to pink at pH 7–9.

Measuring pH19.2

Measuring pH19.2

Universal Indicators

Measuring pH19.2

◦ pH MetersMeasuring pH19.2

Lemons and grapefruits have a sour taste because they contain citric acid. Sulfuric acid is a widely used industrial chemical that can quickly cause severe burns if it comes into contact with skin. You will learn why some acids are weak and some acids are strong.

Strengths of Acids and Bases19.3

Strong acids are completely ionized in aqueous solution.

Weak acids ionize only slightly in aqueous solution.

Strong and Weak Acids and Bases

19.3

Strong bases dissociate completely into metal ions and hydroxide ions in aqueous solution.

NaOH (aq) Na+ (aq) + OH- (aq)

Weak bases partially react with water to form the hydroxide ion.

Strong and Weak Acids and Bases

19.3

H2O

Strong and Weak Acids and Bases

19.3

Excess hydrochloric acid in the stomach can cause heartburn and a feeling of nausea. Antacids neutralize the stomach acid and relieve the pain of acid indigestion. You will learn what a neutralization reaction is.

Neutralization Reactions19.4

The reaction of an acid with a base produces water and a salt.

A salt is an ionic compound whose (+) ion is not H+ and whose (–) ion is not OH-

These double replacement reactions are called neutralization reactions.

Acid-Base Reactions19.4

KOH + HCl

H2SO4 + NaOH

H3PO4 + Ca(OH)2

Net neutralization:

Neutralization Reactions

Acid-Base Reactions19.4

◦ Adding a solution of known concentration to determine the concentration of another solution is called titration.

The solution of known concentration is called the standard solution.

Indicators are used to determine when enough of the standard solution has been added to neutralize the acid or base (end point).

A simple calculation can then find the unknown concentration

Titration19.4

Titration

Acid solution with

indicator

Added base is measured with

a buret.

Color change shows

neutralization.

19.4

Titration To solve titration problems the following

equation is used: (ref table T)

Be sure to use the molarity of the hydrogen and hydroxide ions and the not solutions!

Titration calculation◦ In solving titration problems, the concentrations of

the hydrogen ions (H+) and hydroxide ions (OH-) must be used. These are not necessarily the same as the solution concentration!

What is the concentration of hydrogen or hydroxide ions in the following solutions? 1.5 M HCl

2.0 M H2SO4

0.5 M Ca(OH)2

O.1 M NaOH

◦ Calculate the molarity of an HCl solution if 15.0 mL of it is neutralized by 30.0 mL 0f 0.1 M NaOH.

Titration