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 equation for the autoionization of water and the expression for K_w, and explain why water is left out of it. (Guide: “Water’s own equilibrium”; Practice Q7(c))
- I can state that K_w = 1.0 × 10⁻¹⁴ at 25 °C and that it applies to every aqueous solution, not only pure water. (Guide; Practice Q1)
- I can explain that H⁺(aq) and H₃O⁺(aq) stand for the same ion. (Guide: “A note on notation”)
- I can define acidic, basic and neutral solutions by comparing [H₃O⁺] with [OH⁻]. (Guide: “Neutral means equal”; Practice Q4)
Calculation
- I can calculate pH and pOH from [H₃O⁺] or [OH⁻], and give the pH to the right number of decimal places. (Guide: “pH and pOH: a log scale for tiny numbers”; Practice Q3, Q6(a))
- I can convert a pH or pOH back into a concentration. (Guide: Worked example 1; Practice Q5)
- I can find [OH⁻] from [H₃O⁺] (or the reverse) using K_w. (Practice Q1, Q7(a))
- I can use pH + pOH = pK_w, including at temperatures other than 25 °C. (Guide: Worked example 2; Practice Q3)
- I can turn a difference in pH into a factor change in [H₃O⁺] or [OH⁻]. (Guide: Worked example 3; Practice Q2)
- I can calculate the pH of pure water from a given K_w at any temperature. (Practice Q3, Q6(a))
Reasoning
- I can explain why pure water above 25 °C has pH below 7 but is still neutral. (Guide: “Neutral means equal”; Practice Q6(b))
- I can use the change of K_w with temperature to decide that autoionization is endothermic. (Practice Q6(c))
- I can use Q and K_w, or Le Châtelier’s principle, to explain why adding acid lowers [OH⁻]. (Guide: “The K_w relationship holds in every aqueous solution”; Practice Q7(b))
All ticked? Move on to Topic 8.2, pH and pOH of Strong Acids and Bases, or return to the course roadmap.