What happens to the ammonium cation (NH4+) when the pH is much lower than its pKa of about 9.3?

When the pH is much lower than the pKa of ammonium cation (NH4+), it indicates an acidic environment. In this scenario, we can expect the ammonium cation to remain in its protonated form (NH4+), as the pH is not high enough to favor the deprotonation process.

So, among the options provided:

  • A: None of the molecules have a charge – This statement is incorrect because the ammonium ion (NH4+) carries a positive charge.
  • B: It is deprotonated and negatively charged – This statement is also incorrect since the low pH prevents the deprotonation of NH4+. Instead, it stays as NH4+ and does not become negatively charged.

In summary, at a pH much lower than the pKa, the ammonium cation exists predominantly in its charged form (NH4+), and therefore, the correct answer is neither of the provided statements accurately describes the behavior of ammonium at these pH levels.

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