Determining whether the predominant species in a reaction is charged or neutral
Moderators: Chem_Mod, Chem_Admin
-
- Posts: 103
- Joined: Wed Sep 30, 2020 10:00 pm
Determining whether the predominant species in a reaction is charged or neutral
For week 10 sapling questions #13 and #14, how do we determine whether the predominant species is neutral or charged. For both of the questions, the reactions were neutral, but both questions had different conditions such as when the ph was greater than the pka for #14 and where the pka was greater than the pH for #13. Why is the answer neutral for both? I thought when the ph was greater than the pka, the reaction was neutral and deprotonated (basic), while if the pH was less than the pka, the reaction was charged and protonated (acidic).
-
- Posts: 116
- Joined: Wed Sep 30, 2020 9:40 pm
- Been upvoted: 1 time
Re: Determining whether the predominant species in a reaction is charged or neutral
For an Acid if pH<pKa then its neutral (HA). if pH>pKa its negatively charged (A-)
For Base if pH <pKa then its positive (BH+) if pH>pKa then its neutral (B).
For Base if pH <pKa then its positive (BH+) if pH>pKa then its neutral (B).
-
- Posts: 105
- Joined: Wed Sep 30, 2020 9:52 pm
Re: Determining whether the predominant species in a reaction is charged or neutral
I remember one of the answers being charged and the other being neutral? Not sure though, I don't have it pulled up. For a general explanation, the way I thought of it was that pKa refers to the acidity of the species you're putting into the solution, and pH is the acidity of the solution itself. If the pKa of the acid you're putting in is higher than the pH of the solution, this means the solution is already more acidic than the species; therefore the species will not be likely to dissociate and donate its H+ ions. Conversely, if you have a base where the pKa is higher than the pH of the solution, then the base will be more likely to dissociate and donate its OH- ions because the solution is more acidic --> less basic than the species. Hope this helps!
-
- Posts: 143
- Joined: Wed Sep 30, 2020 9:37 pm
- Been upvoted: 2 times
Re: Determining whether the predominant species in a reaction is charged or neutral
My #13 and #14 were both charged, so I think I might have a different problem than you do. I'll try my best to help anyway!
If the pH is greater than the pKa, the predominant species will be charged because the species will donate its proton.
If the pH is less than the pKa, the predominant species will be neutral because the species does not donate its proton.
For your #14, where the pH is greater than the pKa, it should be charged if it's a weak acid. I think there might be something you're missing in the problem. Maybe it's a strong acid in your problem? If not, it might be worth it to just see the solution that Dr. Lavelle gave.
If the pH is greater than the pKa, the predominant species will be charged because the species will donate its proton.
If the pH is less than the pKa, the predominant species will be neutral because the species does not donate its proton.
For your #14, where the pH is greater than the pKa, it should be charged if it's a weak acid. I think there might be something you're missing in the problem. Maybe it's a strong acid in your problem? If not, it might be worth it to just see the solution that Dr. Lavelle gave.
Return to “Conjugate Acids & Bases”
Who is online
Users browsing this forum: No registered users and 5 guests