Acids and Bases: Foundations for GOB Chemistry (CHE 1120)

Acids and Bases

Introduction to Acids and Bases

Acids and bases are fundamental concepts in general, organic, and biological chemistry. Understanding their properties, definitions, and reactions is essential for studying chemical processes in both laboratory and biological contexts.

• Acids are substances that can donate hydrogen ions (H+) in aqueous solutions.

• Bases are substances that can accept hydrogen ions or produce hydroxide ions (OH-) in aqueous solutions.

• Acids typically taste sour, while bases taste bitter or chalky and feel slippery.

Arrhenius Definition of Acids and Bases

The Arrhenius definition is one of the earliest and simplest ways to classify acids and bases based on their behavior in water.

• Arrhenius Acid: A substance that produces H+ ions when dissolved in water.

• Arrhenius Base: A substance that produces OH- ions when dissolved in water.

• Example: Hydrochloric acid (HCl) dissociates in water to form H+ and Cl- ions: $\mathrm{HCl}(aq) \rightarrow \mathrm{H}^+(aq) + \mathrm{Cl}^-(aq)$

• Example: Sodium hydroxide (NaOH) dissociates in water to form Na+ and OH- ions: $\mathrm{NaOH}(s) \rightarrow \mathrm{Na}^+(aq) + \mathrm{OH}^-(aq)$

Properties of Acids and Bases

Acids and bases can be distinguished by their physical and chemical properties.

• Acids:

  • Produce H+ ions in water

  • Taste sour

  • Turn litmus paper red

  • React with metals

  • Are electrolytes (conduct electricity in solution)

• Bases:

  • Produce OH- ions in water

  • Taste bitter or chalky

  • Feel slippery

  • Turn litmus paper blue

  • Are electrolytes

Characteristic	Acid	Base
Produces H+ in water	Yes	No
Produces OH- in water	No	Yes
Taste	Sour	Bitter, chalky
Touch	May sting	Soapy, slippery
Litmus paper	Red	Blue
Electrolyte	Yes	Yes

Bronsted-Lowry Theory of Acids and Bases

The Bronsted-Lowry theory expands the definition of acids and bases beyond aqueous solutions.

• Bronsted-Lowry Acid: A substance that donates a proton (H+).

• Bronsted-Lowry Base: A substance that accepts a proton (H+).

• Example: In the reaction between hydrochloric acid and water: $\mathrm{HCl} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{Cl}^- + \mathrm{H}_3\mathrm{O}^+$ HCl is the acid (proton donor), H2O is the base (proton acceptor).

Conjugate Acid-Base Pairs

Every acid-base reaction involves conjugate acid-base pairs, which are related by the gain or loss of a proton.

• Conjugate Acid: The species formed when a base gains a proton.

• Conjugate Base: The species formed when an acid loses a proton.

• General Reaction: $\mathrm{HA} + \mathrm{B} \rightleftharpoons \mathrm{A}^- + \mathrm{HB}^+$

• Example: Ammonia and water: $\mathrm{NH}_3 + \mathrm{H}_2\mathrm{O} \rightleftharpoons \mathrm{NH}_4^+ + \mathrm{OH}^-$ NH3 is the base, NH4+ is its conjugate acid; H2O is the acid, OH- is its conjugate base.

Acid	Conjugate Base	Base	Conjugate Acid
HCl	Cl-	NH3	NH4+
HNO3	NO3-	HCO3-	H2CO3
HS-	S2-	OH-	H2O

Counting Atoms: Avogadro's Number

Avogadro's number is a fundamental constant used to count atoms, molecules, or ions in chemistry.

• Definition: One mole of any substance contains $6.022 \times 10^{23}$ entities (atoms, molecules, ions).

• Application: Used to relate macroscopic amounts of substances to the number of particles present.

• Example: One mole of carbon atoms contains $6.022 \times 10^{23}$ carbon atoms.

Chemical Concepts: Atomic Structure and Bonding

Understanding atomic structure and bonding is essential for grasping acid-base behavior and chemical reactivity.

• Atoms: The basic units of matter, composed of protons, neutrons, and electrons.

• Atomic Number: Number of protons in the nucleus; determines the element.

• Atomic Mass: Sum of protons and neutrons in the nucleus.

• Electron Shells: Electrons occupy energy levels around the nucleus.

• Covalent Bonds: Atoms share electrons to achieve stable electron configurations.

• Valence Rules: Atoms tend to have 2 or 8 electrons in their outer shell (octet rule).

• Electronegativity: The tendency of an atom to attract electrons in a bond.

• Ions: Atoms or molecules with a net positive or negative charge due to loss or gain of electrons.

Summary Table: Key Acid-Base Concepts

Concept	Definition	Example
Arrhenius Acid	Produces H+ in water	HCl
Arrhenius Base	Produces OH- in water	NaOH
Bronsted-Lowry Acid	Proton donor	HNO3
Bronsted-Lowry Base	Proton acceptor	NH3
Conjugate Acid	Base + H+	NH4+
Conjugate Base	Acid - H+	Cl-
Avogadro's Number	Number of entities in a mole	$6.022 \times 10^{23}$

Additional info:

• Some content inferred from context and standard GOB Chemistry curriculum, including the summary tables and expanded explanations.

• Periodic table references are foundational for understanding atomic structure and chemical reactivity.