Organic Isoelectric point pH

[txchexmex]

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Topscore mentions that above the isoelectric point pH, a molecule should have a negative charge. So if the isoelectric point is pH=5.91, at pH of 10, the molecule should be overall negative.

Does this mean that if it asks me at pH of 4, the molecule would have an overall positive charge?

TIA

 

[bryantje]

Exactly, because if pH<pI, the carboxyl group will be protonated, whereas when pH>pI, the carboxyl group is actually a carboxylate. Just think "protonation" when you see "low pH" because low pH means that there are a ton of H+ ions floating around.