HW Week 10 Achieve #13

[Alyssa Ly 2G]

Hello!

Can someone explain to me how to work through this problem? What exactly is a predominant species?

"A monoprotic weak acid, HA , is ionized according to the reaction

HA(aq)+H2O(l)↽−−⇀A−(aq)+H3O+(aq) pKa=3.61

where A− is the conjugate base to HA.
For this weak monoprotic acid, the predominant species present at pH 6.47 is unknown, charged, or neutral?"

Thank you!

[N Kanuri 2E]

When the pH = pK_a of a weak acid, there are equal amounts of the neutral species (HA) and the charged, deprotonated species (A^-) in the solution. When pH > pK_a, A^- is more predominant, and when pH < pK_a, HA is more predominant.

[Molly McAndrew 1 1H]

If the pH of the solution is equal to the pK_a of the weak acid, there are equal amounts of HA (neutral, protonated) and A^- (charged, deprotonated). If pH value is greater than pK_a, A^- is more predominant. If pH value is lower than pK_a, HA is more predominant. In this case, pH is 2.38 and pK_a is 4.45. Therefore, pH value is lower and the HA species is more predominant (i.e. the neutral species).

[Naomi Christian 1E]

When pH is greater than pKa the acid is negatively charged. A- is more predominant so it is charged.

[MaiVyDang2I]

When pH > pKa, that means [H+] is low (pH is inversely proportional to [H+]) so [HA] is low and [A-] is high, so [A-] would be the predominant species. And A- is negatively charged.