Acids and bases

Summary and Exam Tips for Acids and Bases

Acids and bases is a subtopic of Equilibria in A-Level Physical Chemistry, which falls under the subject Chemistry in the Cambridge International A Levels curriculum. This section covers key concepts such as conjugate acids and bases, pH calculations, buffer solutions, and the solubility product. A conjugate acid forms when a base accepts a proton, while a conjugate base forms when an acid donates a proton, as per the Bronsted-Lowry theory. The pH scale ranges from 0 to 14, with acids having a pH less than 7 and bases more than 7. The acid dissociation constant ($K_a$) and its logarithmic form ($pK_a$) help determine the strength of acids. The ionic product of water ($K_w$) is crucial for calculating pH in solutions. Buffer solutions maintain a stable pH by using a weak acid and its conjugate base, important in biological systems like blood. The solubility product ($K_{sp}$) describes the equilibrium between a solid and its ions in a saturated solution, while the common ion effect influences solubility by shifting equilibrium positions.

Exam Tips

• Understand Conjugate Pairs: Remember that conjugate acid-base pairs differ by one proton. Practice identifying these pairs in chemical reactions.
• Master pH Calculations: Be comfortable with the formula $\text{pH} = -\log_{10} [H^+]$ and its rearrangement to find $[H^+]$.
• Buffer Solutions: Know how buffers work and their importance in maintaining pH, especially in biological contexts like blood.
• Solubility Product: Familiarize yourself with $K_{sp}$ calculations and the impact of the common ion effect on solubility.
• Practice Problems: Regularly solve problems related to these concepts to reinforce your understanding and improve your calculation skills.