Organic Chemistry

Learn the toughest concepts covered in Organic Chemistry with step-by-step video tutorials and practice problems by world-class tutors.

3. Acids and Bases

Equilibrium Constant

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Now that we understand what an acid is, we need a method of quantifying which acids are stronger and which are weaker. pH doesn’t work for this, let me explain why:

pH vs. pKa

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Why we use pKa instead of pH.

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The Ka (dissociation constant) describes the tendency of a molecule to break apart. In the case of acids, that specifically means donating protons, which is exactly what we are interested in knowing!

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The relationship between equilibrium constant and pKa.

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The pH scale vs. the pKa scale.

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The pH and pKa scales really are completely different. Pardon my French! pKas are obviously something I’m really passionate about. 

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Calculating pKa

This is the easiest kind of question you could get. Calculating pKa’s just takes some very simple math. 

What is the pKa of acetic acid? Hint:take the negative log of the dissociation constant.

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Calculate the pKa of acetic acid

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What is the pKa of ammonium? Hint:take the negative log of the dissociation constant.

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Calculating pKa and comparing acidity

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