Carboxylic acids containing -COOH , such as acetic and lactic acids, normally have a Ka constant of about 10 -3 to 10 Consequently, expressing acidity in terms of the Ka constant alone can be inconvenient and not very intuitive. Therefore, pKa was introduced as an index to express the acidity of weak acids, where pKa is defined as follows.
In addition, the smaller the pKa value, the stronger the acid. For example, the pKa value of lactic acid is about 3. Another important point is the relationship between pH and the pKa of an acid. Create a personalised ads profile. Select personalised ads. Apply market research to generate audience insights. Measure content performance. Develop and improve products. List of Partners vendors.
Share Flipboard Email. Anne Marie Helmenstine, Ph. Chemistry Expert. Helmenstine holds a Ph. She has taught science courses at the high school, college, and graduate levels. Facebook Facebook Twitter Twitter. While this course begins with single functional groups, we will eventually work with interesting compounds containing multiple functional groups. Recognizing which hydrogens can be ionized as acidic protons and which hydrogens can NOT, is a useful skill.
Notice in this example that we need to evaluate the potential acidity at four different locations on the molecule. Aldehyde and aromatic protons are not at all acidic pK a values are above 40 — not on our table.
The two protons on the carbon next to the carbonyl are slightly acidic, with pK a values around according to the table. The most acidic proton is on the phenol group, so if the compound were to be subjected to a single molar equivalent of strong base, this is the proton that would be donated. Because our goal is understanding dynamic chemical reactivity, we do NOT need to know the specific amount of the protonated and unprotonated forms of a compound.
We simply need to know which form is predominate. Donate Login Sign up Search for courses, skills, and videos. Science Chemistry library Buffers, titrations, and solubility equilibria Buffer solutions. Introduction to buffers. Henderson—Hasselbalch equation.
Common ion effect and buffers. Buffer solution pH calculations. Methods for preparing buffers. Next lesson. Current timeTotal duration Google Classroom Facebook Twitter. And specifically, we're going to be talking mostly about this in terms of the Henderson-Hasselbalch equation.
But before we go to the Henderson-Hasselbalch equation, which I am gonna assume you've seen before, and if not we have some other videos introducing it and also deriving it, let's do a quick review of what exactly is a buffer.
So a buffer is something that contains an aqueous solution.
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