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 write the Henderson-Hasselbalch equation with the base on top of the ratio, and say what each term means. (Guide: “From K_a to a buffer equation”)
- I can explain that the equation is the K_a expression in log form, so it only applies at equilibrium. (Guide: “From K_a to a buffer equation”)
- I can say whether a buffer’s pH is above, below or equal to its pKa just from the ratio [A⁻]/[HA]. (Guide: “Reading the equation”; Practice Q6(d))
- I can explain why the amounts mixed can be used in place of equilibrium amounts in a buffer. (Guide: “Why the starting amounts work”)
Calculation
- I can calculate the pH of a buffer from the pKa (or K_a) and the concentrations of the pair. (Guide: Worked example 1; Practice Q1)
- I can calculate buffer pH after mixing two solutions, working in moles. (Guide: Worked example 2; Practice Q5)
- I can use the pKa of NH₄⁺ (or 14.00 − pKb) for a weak-base buffer. (Practice Q3)
- I can find the ratio of components needed for a target pH, and the amount of one component. (Guide: Worked example 3; Practice Q2, Q7(b))
- I can find a buffer’s composition after a weak acid is partly neutralised by a strong base, then find its pH. (Practice Q6)
- I can find a pKa from a measured buffer pH and a known ratio. (Guide: Worked example 4)
Reasoning
- I can choose the best conjugate pair for a target pH and justify it using pKa and the ratio range. (Guide: Worked example 3; Practice Q7)
- I can explain, in words, why adding a little acid or base changes a buffer’s pH only slightly. (Guide: “Why a small addition barely changes the pH”; Practice Q4)
- I can explain why diluting a buffer with water does not change its pH. (Guide: “Moles or concentrations?”)
All ticked? Move on to Topic 8.10, Buffer Capacity, or return to the course roadmap.