Acids, Bases, Salts, and Related Chemical Concepts: Study Guide

Objectives of the Unit: Acids, Bases, and Salts

Overview

This unit covers essential concepts related to acids, bases, salts, and their chemical properties. Students will learn to define key terms, understand physical and chemical characteristics, and apply these concepts to chemical reactions and solution chemistry.

Oxidation Number

Definition and Calculation

• Oxidation number (or oxidation state) is the hypothetical charge an atom would have if all bonds to atoms of different elements were 100% ionic.

• It is used to track electron transfer in chemical reactions, especially in redox (oxidation-reduction) reactions.

• Rules for assigning oxidation numbers:

  • Elemental form: Oxidation number is 0 (e.g., O2, N2).

  • Monatomic ion: Equal to the ion's charge (e.g., Na+ is +1).

  • Oxygen: Usually -2 (except in peroxides, where it is -1).

  • Hydrogen: +1 when bonded to nonmetals, -1 when bonded to metals.

  • Sum of oxidation numbers in a neutral compound is 0; in a polyatomic ion, it equals the ion's charge.

• Example: In H2SO4, H is +1, O is -2, S is +6.

Acids, Bases, and Salts

Definitions

• Acid: A substance that donates protons (H+) in aqueous solution. Example: HCl.

• Base: A substance that accepts protons or donates hydroxide ions (OH-). Example: NaOH.

• Salt: An ionic compound formed from the neutralization reaction of an acid and a base. Example: NaCl.

Physical and Chemical Characteristics of Acids and Bases

Properties

• Acids:

  • Taste sour

  • Turn blue litmus paper red

  • React with metals to produce hydrogen gas

  • pH less than 7

• Bases:

  • Taste bitter

  • Feel slippery

  • Turn red litmus paper blue

  • pH greater than 7

• Chemical characteristics: Acids and bases react in neutralization reactions to form salts and water.

pH, Neutralization, and Related Terms

Definitions and Applications

• pH: A measure of the hydrogen ion concentration in a solution. Defined as $pH = -\log[H^+]$.

• Neutralization: The reaction between an acid and a base to produce a salt and water. Example: $HCl + NaOH \rightarrow NaCl + H_2O$.

• Example: Mixing vinegar (acetic acid) and baking soda (sodium bicarbonate) results in neutralization.

Types of Salts

Classification and Differentiation

• Normal salts: Formed by complete replacement of hydrogen ions of an acid by a metal or ammonium ion. Example: NaCl.

• Acidic salts: Formed when not all hydrogen ions are replaced. Example: NaHSO4.

• Basic salts: Formed when a base is not completely neutralized. Example: Mg(OH)Cl.

• Double salts: Contain more than one cation or anion. Example: alum (KAl(SO4)2·12H2O).

Methods of Salt Preparation

Common Laboratory Methods

• Neutralization: Reacting an acid with a base.

• Direct combination: Reacting elements directly (e.g., Na + Cl2).

• Reaction of acid with metal: Produces salt and hydrogen gas.

• Reaction of acid with carbonate: Produces salt, water, and carbon dioxide.

• Example: $2HCl + Na_2CO_3 \rightarrow 2NaCl + H_2O + CO_2$

Electrolytes and Nonelectrolytes

Definitions and Differences

• Electrolytes: Substances that conduct electricity when dissolved in water due to the presence of ions. Example: NaCl.

• Nonelectrolytes: Substances that do not conduct electricity in solution because they do not produce ions. Example: sugar (C12H22O11).

• Applications: Electrolytes are important in biological systems for nerve conduction and muscle contraction.

Comparison Table: Electrolytes vs. Nonelectrolytes

Property	Electrolytes	Nonelectrolytes
Conductivity	Conducts electricity in solution	Does not conduct electricity
Ion formation	Forms ions in solution	No ions formed
Examples	NaCl, HCl, KNO3	Sugar, ethanol