The nitrite ion has Kb = 2.17 x 10^-11. What is Ka for nitrous acid, its conjugate acid?

1. For a conjugate pair the two constants multiply to give the ion product for water. 2. So the acid constant is the ion product divided by the base constant. 3. Substitute: 1.0 x 10^-14 divided by 2.17 x 10^-11. 4. Divide the coefficients: 1.0 divided by 2.17 is 0.46. 5. Subtract the exponents: minus 14 minus minus 11 gives minus 3. 6. Combine: 0.46 x 10^-3, which is written as 4.6 x 10^-4. 7. Multiplying the two constants instead of dividing gives the trap value near 10^-25. 8. This route is how a missing acid constant is obtained when only the base value is tabulated. _Source: OpenStax Chemistry (CC BY 4.0), Ch 14 "Acid-Base Equilibria", section 14.3 Relative Strengths of Acids and Bases_