● The expression for the dissociation constant of a weak acid (Ka) and a weak base (Kb).
● For a conjugate acid–base pair, Ka Å~ Kb = Kw.
Guidance
● The value Kw depends on the temperature.
● Only examples involving the transfer of one proton will be assessed.
● Calculations of pH at temperatures other than 298 K can be assessed.
● The relationship between Ka and pKa is pKa = –logKa and between Kb and pKb is pKb = –logKb.

● Solution of problems involving [H+(aq)], [OH–(aq)], pH, pOH, Ka, pKa, Kb, and pKb.
Guidance
● Students should state when approximations are used in equilibrium calculations.
● The use of quadratic equations will not be assessed.
● Discussion of the relative strengths of acids and bases using values of Ka, pKa, Kb, and pKb.
Guidance
The calculation of pH in buffer solutions will only be assessed in options B.7 and D.4.

18.2 What are the dissociation constant for weak acids and bases 
​18.2 What is the relationship between Ka and pKa is pKa = –logKa and between Kb and pKb is pKb = –logKb?

18.2 How can [H + (aq)], [OH – (aq)], pH, pOH, Ka , pKa , Kb , and pKb  be identified in different acid base problems?
​18.2 How can you calculate the pH in a buffer solution?

18.2 To what extent are buffer solution used in industry?

Explanation how pH and Kw are linked 
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Follow the exercise that explains how you can determine Kw
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Explanation on Acid Strength
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