Problem: The odor of fish is due primarily to amines, especially methylamine (CH3NH2). Fish is often served with a wedge of lemon, which contains citric acid. The amine and the acid react forming a product with no odor, thereby making the less-than-fresh fish more appetizing.Using data from Appendix D in the textbook, calculate the equilibrium constant for the reaction of citric acid with methylamine, if only the first proton of the citric acid (Ka1) is important in the neutralization reaction.

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We are asked to calculate the equilibrium constant for the reaction of citric acid with methylamine, if only the first proton of the citric acid (Ka1) is important in the neutralization reaction.

Recall: Weak acids possess a Ka value less than 1, while weak bases possess a Kb value less than 1. 


The equilibrium expressions of Ka and Kb are the same as other equilibrium constants we’ve seen.

Ka = productsreactants = A-H+[HA]

Kb = productsreactants = HAOH-[A-]


The relationship of Ka and Kb for an acid-base conjugate pair:

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Problem Details

The odor of fish is due primarily to amines, especially methylamine (CH3NH2). Fish is often served with a wedge of lemon, which contains citric acid. The amine and the acid react forming a product with no odor, thereby making the less-than-fresh fish more appetizing.

Using data from Appendix D in the textbook, calculate the equilibrium constant for the reaction of citric acid with methylamine, if only the first proton of the citric acid (Ka1) is important in the neutralization reaction.

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