Work through the list without notes. If you cannot do a statement, follow its link, then come back. Guide = study guide; Practice = practice questions.
Understanding
- I can explain what the acid form and the base form of a weak acid are, and what “predominant form” means. (Guide: “Two forms of the same substance”)
- I can state which form predominates when pH < pK_a, when pH = pK_a and when pH > pK_a. (Guide: “The rule: compare pH with pK_a”; Practice Q1)
- I can use the rearranged K_a expression to explain why the comparison works. (Guide: “The rule”; Revision notes)
- I can explain why an indicator changes colour, using its protonated and deprotonated forms. (Guide: “Indicators are weak acids you can see”; Practice Q4)
Calculation
- I can calculate [A⁻]/[HA] at a given pH and turn it into a percentage in each form. (Guide: Worked example 1; Practice Q5)
- I can convert a pK_b into the pK_a of the conjugate acid and use it to find the predominant form of a weak base. (Guide: Worked example 1(b); Practice Q2)
- I can find the pH range in which one form makes up at least a given percentage. (Practice Q5(c))
Reasoning and lab skills
- I can estimate an indicator’s pK_a from colour observations in buffers and state how precise the estimate is. (Practice Q6)
- I can choose an indicator for a strong acid–strong base, weak acid–strong base or weak base–strong acid titration. (Guide: Worked example 2; Practice Q3)
- I can explain how a poor indicator choice changes the measured titre and the calculated concentration. (Guide: Figure 2; Practice Q7)
- I can explain why “pH above pK_a” does not mean “fully dissociated”. (Guide: Common misconceptions)
All ticked? Move on to Topic 8.8, Properties of Buffers, or return to the course roadmap.