Study Notes
Acids and bases are fundamental concepts in chemistry, involving the transfer of protons between species. Understanding their behavior is crucial for predicting the outcomes of chemical reactions.
- Conjugate Acid — A species formed when a base accepts a proton (H⁺). Example: NH₄⁺ is the conjugate acid of NH₃.
- Conjugate Base — A species formed when an acid donates a proton (H⁺). Example: Cl⁻ is the conjugate base of HCl.
- Conjugate Acid-Base Pair — Two species that transform into each other by gain or loss of a proton. Example: CH₃COOH and CH₃COO⁻.
- pH — A measure of acidity or basicity of a solution, calculated as pH = -log₁₀ [H⁺]. Example: A solution with [H⁺] = 1 x 10⁻⁷ mol dm⁻³ has a pH of 7.
- Ka — The acid dissociation constant, indicating the strength of a weak acid. Example: Acetic acid has a Ka value of 1.8 x 10⁻⁵.
- pKa — The negative logarithm of the Ka value, used to compare acid strengths. Example: Acetic acid has a pKa of 4.74.
- Kw — The ionic product of water, equal to 1.00 x 10⁻¹⁴ mol² dm⁻⁶ at 298 K. Example: Kw = [H⁺][OH⁻].
- Buffer Solution — A solution that resists changes in pH upon addition of small amounts of acid or base. Example: A mixture of acetic acid and sodium acetate.
Exam Tips
Key Definitions to Remember
- Conjugate acid
- Conjugate base
- pH
- Ka and pKa
- Buffer solution
Common Confusions
- Mixing up conjugate acids and bases
- Misunderstanding the pH scale
- Confusing Ka and pKa values
Typical Exam Questions
- What is a conjugate acid-base pair? A pair of species that differ by a proton.
- How do you calculate the pH of a solution? Use the formula pH = -log₁₀ [H⁺].
- What happens to the pH of a buffer when acid is added? It remains relatively constant due to the buffer action.
What Examiners Usually Test
- Understanding of conjugate acid-base pairs
- Ability to calculate pH from [H⁺]
- Application of buffer solutions in real-world scenarios