(Solved) Indicate whether each of the compounds in the stomach would be in protonated form or as a neutral ba

Polymorphism

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13 years ago

Indicate whether each of the compounds in the stomach would be in protonated form or as a neutral ba

Technically, this is just chemistry and not biochemistry but I'm hoping someone can help me!

Many moderately large organic molecules containing basic nitrogen atoms are not very soluble in water as neutral molecules, but they are frequently much more soluble than their salts. assuming the pH of the stomach is 2.5, indicate whether each of the compounds in the stomach would be in protonated form or as a neutral base:

Compound 1: Kb = 7 x 10^-7
Compound 2: Kb = 4 x 10^-14

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bio_man

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Educator

13 years ago Edited: 13 years ago, bio_man

Both compounds are weak bases because they are less then 1. Bases with a Kb greater than 1 are considered strong bases.

pKb = -log(Kb)
pKb = -log(7 x 10^-7)
= 6.15
pKb = -log(4 x 10^-14)
= 13.39

Recall: pKa + pKb = 14

A lower pKa means a stronger acid. I haven't done chemistry in ages, so I don't know how to interpret these results.

The Kpa or pKb is the point of half neutralizaion of the proton (H+)-donating or -accepting group. This could probably explain it better: http://tiny.cc/biologyforums1.

Did your teacher mention any of these formulas?

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bio_man

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Educator

13 years ago

I updated my answer; though I still haven't reached a conclusion.

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Polymorphism Author

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13 years ago

Yes, I know all of the formulas and how to use them, but there is just no way to compare pH to pKa without being given a starting concentration. That's where I am stuck.

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bio_man

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Educator

13 years ago

I suppose that if compound 2 is the stronger acid, it will likely become protonated in an acid solution because acids are generally H+ hungry. The weaker acid, compound 1, is less like become protonated because it is a weak acid.

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karim89

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Posts: 155

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13 years ago

This verified answer contains over 130 words.

2 Votes

slinky, bio_man

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Indicate whether each of the compounds in the stomach would be in protonated form or as a neutral ba

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