How is CN - a weak base if its the conjugate base of a weak acid?

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Chemistry

Yosef Harvey

27 January, 23:52

How is CN - a weak base if its the conjugate base of a weak acid?

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Leland Cortez · Answer 1

The conjugate bases of most weak acids are weak bases.

The only conjugates that are strong bases are those of extremely weak acids, like water (pKa = 14), for which OH - is the conjugate base.

"The conjugate base of a relatively weak weak acid is a relatively strong weak base, and the conjugate base of a relatively strong weak acid is a relatively weak weak base."

NH2 - is the conjugate base of an extremely weak acid, NH3 (pKa = 35). On the otehr hand, CN - is the conjugate base of a moderately weak acid, HCN (pKa = 9.2), so it's a moderately weak base.