The titration curve for glycine is shown below. The key points are designated I to V.

Select the the point on the titration curve where the average net charge of glycine is zero

Question

The titration curve for glycine is shown below. The key points are designated I to V.

Select the the point on the titration curve where the average net charge of glycine is zero

BlackTom AI · Accepted Answer

To determine where the average net charge of glycine is zero, we should consider glycine's amino and carboxyl groups and their pKa values. As the molecule is titrated, the net charge passes through zero at its isoelectric point (pI).

Option I: This point occurs at very low OH- equivalents and corresponds to a highly protonated species with a positive net charge, not zero.

Option II: This location aligns with the first deprotonation step (carboxyl group losing a proton), giving glycine a negative charge but not yet neutral overall; the net charge is still not zero here.

Option III: This point sits around pH 5.97, which is the pI of glycine. At this pH, the average net charge of glycine is zero because the molecule has equal populations of positively and negatively charged forms when the two ionizable groups balance each other.

Option IV: This region corresponds to a higher pH where the amino group begins to deprotonate and the molecule carries a negative charge, so the net charge is not zero.

Option V: At very high pH, both groups are deprotonated, giving a strongly negative net charge, far from zero.

In summary, the net charge is zero at the isoelectric point, which for glycine occurs near pH 6 and corresponds to point III on the curve.

AGRI20043_2025_SM1 Workshop 2 Quiz

The titration curve for glycine is shown below. The key points are designated I to V. Select the the point on the titration curve where the average net charge of glycine is zero

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The titration curve for glycine is shown below. The key points are designated I to V. Click on the region of the titration curve that represents the isoelectric point (pI) of glycine

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