8.3 Properties of Acids and Bases

Acid • Compound that produces hydronium ions (H3O+)

when dissolved in water.

• Properties of an acid include:

– Sour taste

• Ex: different fruits, vinegar. Do not test an acid by tasting it.

– Reactivity with metals

• Reaction between an acid and a metal is a single replacement reaction.

– Ability to turn blue litmus paper red

• Proton donor

Base • Compound that produces hydroxide ions

(OH-) when dissolved in water.

• Properties of a base include:

–Bitter taste

–Slippery feel

–Ability to turn red litmus paper blue

• Proton acceptor

Neutralization and Salts • The reaction between an acid and a base is called

neutralization.

• The neutralization reaction between an acid and a base produces a salt and water.

-The negative ions in an acid combine with the positive ions in a base to produce an ionic compound called a salt.

-The hydronium ions from the acid combine with the hydroxide ions from the base to produce water.

Neutralization and Salts • Table salt is the most common example of a salt compound.

8.4 Strength of Acids and Bases

The pH Scale • Scale, numbered 0-14, used by chemists to

describe the concentration of hydronium ions in a solution.

• pH=7 is neutral

• pH < 7 is an acid

• pH > 7 is a base

• Lower pH=greater H3O+ (hydronium) ion concentration in solution

• Higher pH=lower H3O+ (hydronium) ion concentration in solution

Strong Acids and Bases • When strong acids dissolve in water,

they ionize almost completely.

–HCl

• Strong bases dissociate (separates into ions as it dissolves) almost completely in water.

–Sodium hydroxide

Weak Acids and Bases • Weak acids and bases ionize or

dissociate only slightly in water.

–Weak acid=citric acid in orange juice or acetic acid in vinegar

–Weak base=toothpaste and shampoo

Buffers • Solution that is resistant to

large changes in pH.

• Made from a weak acid and its salt or a weak base and its salt.

• pH of buffers remain relatively constant

Electrolytes • Substance that ionizes or dissociates into ions

when it dissolves in water.

– The resulting solution can conduct an electric current.

– Can be classified as strong or weak.

• Strong acids and bases are strong electrolytes because they dissociate or ionize almost completely in water.