A primary amino group reacts with nitrous acid: R-NH₂ + HNO₂ → R-OH + N₂ + H₂O…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A primary amino group reacts with nitrous acid: . A sample of of glycine () reacts completely. Take the molar volume of a gas as . Find the amount of glycine and the volume of nitrogen gas. Say whether proline would give the same volume per gram.
Need a reminder? The key ideaShow
The isoelectric point is the pH at which the average charge is zero. For a neutral side chain, . For other amino acids, average the two pK values on either side of the neutral form. The fraction of a group that is still protonated is for a group that is positive when protonated.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Plan. One amino group gives one .
Step 1. Moles. .
Step 2. Nitrogen. .
Step 3. Proline. Proline has a secondary amine group, which does not give off nitrogen in this test. It would give no gas.
Answer: and of nitrogen. Proline would not give the same volume.
Check. One mole of nitrogen occupies , so a few millimoles give a fraction of a litre.
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