7.3 Properties of Acids and Bases

Acids and bases are key players in chemistry, affecting everything from our body's pH to industrial processes. They're defined by their ability to donate or accept protons, with different definitions expanding their scope beyond just water-based reactions.

Strong acids and bases fully break apart in water, while weak ones only partially dissociate. This affects their behavior in solutions and reactions. Understanding acid-base strength and reactions is crucial for predicting chemical outcomes and balancing pH in various applications.

Acids and Bases Definitions

Fundamental Acid and Base Concepts

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• Acid donates protons (H+ ions) in aqueous solutions
• Base accepts protons (H+ ions) in aqueous solutions
• Arrhenius definition classifies acids as substances that increase H+ ion concentration in water
• Arrhenius definition identifies bases as substances that increase OH- ion concentration in water
• Brønsted-Lowry definition expands acid concept to proton donors in any solution
• Brønsted-Lowry definition broadens base concept to proton acceptors in any solution

Comparative Analysis of Acid-Base Definitions

• Arrhenius definition limits acids and bases to aqueous solutions
• Brønsted-Lowry definition applies to non-aqueous solutions and gas-phase reactions
• Arrhenius acids produce H+ ions when dissolved in water (HCl, H2SO4)
• Arrhenius bases produce OH- ions when dissolved in water (NaOH, KOH)
• Brønsted-Lowry acids transfer protons to other molecules or ions (NH4+, H3O+)
• Brønsted-Lowry bases accept protons from other molecules or ions (NH3, CO32-)

Acid and Base Strength

Characteristics of Strong and Weak Acids

• Strong acid completely dissociates in aqueous solutions
• Strong acids have a high degree of ionization (HCl, HNO3, H2SO4)
• Weak acid partially dissociates in aqueous solutions
• Weak acids have a low degree of ionization (CH3COOH, HF, H2CO3)
• Strong acids have lower pKa values than weak acids
• Weak acids establish equilibrium between molecular and ionic forms in solution

Properties of Strong and Weak Bases

• Strong base completely dissociates in aqueous solutions
• Strong bases have a high degree of ionization (NaOH, KOH, Ca(OH)2)
• Weak base partially dissociates in aqueous solutions
• Weak bases have a low degree of ionization (NH3, CH3NH2)
• Strong bases have higher pKb values than weak bases
• Weak bases establish equilibrium between molecular and ionic forms in solution

Factors Affecting Acid and Base Strength

• Molecular structure influences acid and base strength
• Electronegativity of atoms in the molecule affects proton donation or acceptance
• Bond strength between proton and rest of molecule impacts acid strength
• Stability of conjugate base or acid affects overall strength
• Concentration affects the apparent strength of acids and bases in solution
• Temperature can influence the degree of dissociation for weak acids and bases

Acid-Base Reactions

Conjugate Acid-Base Pairs

• Conjugate acid-base pair consists of two species differing by one proton
• Acid donates a proton to become its conjugate base
• Base accepts a proton to become its conjugate acid
• Strength of acid inversely related to strength of its conjugate base
• Strong acids have weak conjugate bases (HCl and Cl-)
• Weak acids have strong conjugate bases (CH3COOH and CH3COO-)
• Conjugate pairs play crucial role in buffer solutions

Acid-Base Indicators and Their Applications

• Indicators change color based on pH of solution
• Weak acids or bases with distinct colors in protonated and deprotonated forms
• Phenolphthalein changes from colorless in acidic solutions to pink in basic solutions
• Methyl orange transitions from red in acidic solutions to yellow in basic solutions
• Litmus paper turns red in acidic solutions and blue in basic solutions
• Universal indicator provides approximate pH measurement through color spectrum
• Indicators used in titrations to determine endpoint of acid-base reactions
• Selection of appropriate indicator depends on pH range of titration