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Lecture 11--pKa and pKb Notes

# Lecture 11--pKa and pKb Notes - 3 COOH 1.8e-5 HClO 2 1.2e-2...

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Ch 302 Notes October 26, 2009 Conjugate Acid/Base Pairs Take Hydrofluoric Acid (HF) for example: K a for HF: K b for F - : Notice that for this conjugate acid/base pair, K a * K b = K W . This is true for any conjugate acid/base pair. As the strength of the acid increases, the strength of the conjugate base will decrease, and vice versa. Look at the relationship between K a and K b for a given acid/base pair. As K a increases, K b must decrease!

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As K a increases, the acid gets stronger. As K b increases, the base gets stronger. Example: Rank the following acids in order of increasing strength. Tank the conjugate bases in terms of increasing strengths. Acid K a HF 7.2e-4 CH
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Unformatted text preview: 3 COOH 1.8e-5 HClO 2 1.2e-2 HCl Very Large pKs Just as the [H + ] concentration can be a small number that is difficult to deal with, so can K a /K b values. Hence, we introduce the concept of the pK: pK a = -log(K a ) and pK b = -log(K b ) Rule: 14 = pK a + pK b for any conjugate acid/base pair at 25 o C. Example: Given the following K a values, compute the pK a of the acid and the K b and pK b of the conjugate bases: K a : 1e-10 1e-3 1 1000 1e10 pK a : K b : pK b : Note that as acid strength increases, the pK a will decrease. As base strength increases, the pK b will decrease. Example:...
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Lecture 11--pKa and pKb Notes - 3 COOH 1.8e-5 HClO 2 1.2e-2...

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