Acids and Bases: Theories and pH Scale

Arrhenius Theory

• Acids: substances that donate a proton (H+)
• Bases: substances that accept a proton (OH-)

Bronsted-Lowry Theory

• Acids: substances that donate a proton (H+)
• Bases: substances that accept a proton
• Conjugate acid: the species formed when a base accepts a proton
• Conjugate base: the species formed when an acid donates a proton

pH Scale

• Measures the concentration of hydrogen ions (H+) in a solution
• pH = -log[H+]
• pH 7: neutral (neither acidic nor basic)
• pH < 7: acidic
• pH > 7: basic

Strong and Weak Acids and Bases

• Strong acids: completely dissociate in water, releasing all H+ ions
  • Examples: HCl, HNO3, H2SO4
• Weak acids: partially dissociate in water, releasing some H+ ions
  • Examples: CH3COOH, HCN, HF
• Strong bases: completely dissociate in water, releasing all OH- ions
  • Examples: NaOH, KOH, Ca(OH)2
• Weak bases: partially dissociate in water, releasing some OH- ions
  • Examples: NH3, CO3^2-, PO4^3-

Acid-Base Reactions

• Neutralization: reaction between an acid and a base to form a salt and water
  • Example: HCl + NaOH → NaCl + H2O
• Acid-base equilibrium: balance between the forward and reverse reactions
  • Example: HCl + H2O ⇌ H3O+ + Cl-

Acid-Base Indicators

• Substances that change color in response to changes in pH
• Used to determine the pH of a solution
• Examples: litmus, phenolphthalein, methyl orange

Arrhenius Theory

• Acids are defined as substances that donate a proton (H+)
• Bases are defined as substances that accept a proton (OH-)

Bronsted-Lowry Theory

• Acids are defined as substances that donate a proton (H+)
• Bases are defined as substances that accept a proton
• Conjugate acid is the species formed when a base accepts a proton
• Conjugate base is the species formed when an acid donates a proton

pH Scale

• Measures the concentration of hydrogen ions (H+) in a solution
• Calculated using the formula: pH = -log[H+]
• pH 7 is neutral, meaning neither acidic nor basic
• Solutions with pH < 7 are acidic
• Solutions with pH > 7 are basic

Strong and Weak Acids and Bases

• Strong acids completely dissociate in water, releasing all H+ ions
  • Examples: HCl, HNO3, H2SO4
• Weak acids partially dissociate in water, releasing some H+ ions
  • Examples: CH3COOH, HCN, HF
• Strong bases completely dissociate in water, releasing all OH- ions
  • Examples: NaOH, KOH, Ca(OH)2
• Weak bases partially dissociate in water, releasing some OH- ions
  • Examples: NH3, CO3^2-, PO4^3-

Acid-Base Reactions

• Neutralization reactions occur between an acid and a base to form a salt and water
  • Example: HCl + NaOH → NaCl + H2O
• Acid-base equilibrium is the balance between the forward and reverse reactions
  • Example: HCl + H2O ⇌ H3O+ + Cl-

Acid-Base Indicators

• Are substances that change color in response to changes in pH
• Used to determine the pH of a solution
• Examples: litmus, phenolphthalein, methyl orange

Understand the concepts of acids and bases according to Arrhenius and Bronsted-Lowry theories, and learn about the pH scale which measures the concentration of hydrogen ions in a solution.