Understanding Acidity: Pka and pH

[babbagee]

I have a question about pka and pH say that the pka of Acetic acid is 4.7 and the ph of the solution is 3.5, that means that the solution is acidic so it wants to donate protons, would that mean that Acetic acid in this solution would be in the protonated form, that means it will not donate it H. Say if pH was no 5.0 which is still acidic but its larger than the pka so that means that Acetic acid is going to be in the deprotonated form. Am i getting this right, if not can someone please clear this up for me. I've always had a hard time with this concept.

Thanks

 

[GCT]

well assuming a pure acetic acid solution, at a pH of 3.5, you'll have mostly the acidic form of acetic acid. Think of it in terms of rate dynamics.

 

[Blueshift5]

for your question. Your understanding is mostly correct. The pka and pH values are both measures of acidity, but they represent different things. The pka is a measure of the strength of an acid, while the pH is a measure of the concentration of hydrogen ions (H+) in a solution. In your example, the pka of Acetic acid is 4.7, meaning that at this pH, half of the acid molecules will be in the protonated form (HAc) and half will be in the deprotonated form (Ac-). This is known as the acid's "half-equivalence point."

Now, let's consider the pH of the solution. At a pH of 3.5, the solution is indeed acidic and will have a higher concentration of H+ ions. This means that there will be more H+ ions available for the Acetic acid molecules to donate, so it will tend to stay in the protonated form. However, as you mentioned, if the pH were to increase to 5.0, the concentration of H+ ions would decrease, and the equilibrium would shift towards the deprotonated form of Acetic acid.

So, in summary, the pka and pH values are related but represent different aspects of acidity. The pka tells us about the strength of an acid, while the pH tells us about the concentration of H+ ions in a solution. I hope this helps clarify the concept for you. Keep asking questions and exploring, that's how we continue to learn and deepen our understanding of scientific concepts.