alleryStart learning →What is the product of Ka for an acid and Kb for its conjugate base?
AIt equals one, whatever the pair chosen
BIt equals the acid constant of pure water
CIt equals the sum of the two constants used
DIt equals Kw, the ion product for water
Answer & Solution
Correct answer: D. It equals Kw, the ion product for water
1. Write the acid ionisation equation and the base ionisation equation of its conjugate.
2. Adding the two equations together leaves the autoionisation of water.
3. When equations are added, their equilibrium expressions are multiplied together.
4. Multiplying the two expressions cancels the acid and conjugate base terms.
5. What remains is the hydronium concentration times the hydroxide concentration, which is Kw.
6. So the product of the pair is 1.0 x 10^-14 at 25 degrees Celsius.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 14 "Acid-Base Equilibria", section 14.3 Relative Strengths of Acids and Bases_
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