Acids and Bases (10th Class)

Acids and Bases

• Non-metal oxides react with water to produce acids, which have a sour taste (acidus means "sour" in Latin).
• Acids have the following properties:
  • Can cause indicators to change color.
  • Produce hydrogen gas when reacting with metals.
  • Produce carbon dioxide with carbonate compounds.
  • Conduct electricity as they ionize in water.

Arrhenius Theory of Acids and Bases (1887)

• Acids dissociate in water to produce one or more hydrogen ions (H+).
• Bases dissociate in water to form one or more hydroxide ions (OH-).

Limitations of Arrhenius Theory

• Hydrogen ions (H+) are always hydrated, forming hydronium ions (H3O+).
• Not all bases contain hydroxide ions (e.g., ammonia).
• Not all acid-base reactions occur in water.

Other Acid-Base Theories

• Bronsted-Lowery:
  • Acids: substances that donate a proton (H+).
  • Bases: substances that accept a proton.
  • Conjugate acid-base pairs differ by a proton.
• Lewis:
  • Acids: accept an electron pair.
  • Bases: donate an electron pair.
  • Allows for a broader definition of acid-base reactions.

Strong and Weak Acids

• Strong acids: completely dissociate in water, producing hydronium ions (H3O+).
• Weak acids: partially ionize, with only a fraction of molecules producing hydronium ions.

Strong and Weak Bases

• Strong bases: completely dissociate in water, producing hydroxide ions (OH-).
• Weak bases: partially dissociate, with only a fraction of molecules producing hydroxide ions.

pH and pOH

• pH: measures the concentration of hydronium ions (H3O+).
• pOH: measures the concentration of hydroxide ions (OH-).
• pH + pOH = 14.

Calculating pH

• pH = -log[H3O+].
• If the concentration of [H3O+] is known, the pH can be calculated.