pH and pKa - Definition, Values, Calculations | [email protected]
So although the pH of a buffer is determined by only the ratio conjugate base and acid, the ability of the buffer to absorb strong acid or base is. Similar to pH, the value of Ka can also be represented as pKa. •. pKa = -log Ka. Note: (The difference between a weak acid and its conjugate base differ is one. We can help you get the relationship between pH and pKa for acid A buffer is a solution of a weak acid and its conjugate base or a weak base and its.
So what we're gonna do, is we're gonna rearrange this equation to solve for this ratio that we might be interested in. And I don't know about you, but I actually find, well, laughs I find logs not super-intuitive sometimes.
So I'm actually going to get rid of the log by raising both sides to the 10th power. So what does this tell us?
It may not look like it tells us a whole lot more, but actually, it tells us a lot. It tells us about the relative relationship and size between A minus and HA concentration.
pH and pKa relationship for buffers (video) | Khan Academy
So if we look at this, we can derive a couple relationships. So let's go ahead and look at all the possible scenarios for these three things. So anything to the zeroth power is equal to one.
Which tells us that this ratio is equal to one. And if A minus concentration over HA concentration is equal to one, that means that they have the same concentration. I forgot a minus sign there. This is a really helpful thing to remember.
And this comes up a lot not just when you're talking about buffers by themselves, but also when you're doing titrations. And the point in your titration where the HA is equal to A minus is called the half-equivalence point.
And if you haven't learnt about buffers, that's okay. Oh, sorry, if you haven't learn about titrations yet, that's fully fine.
pKa and Dissociation Equilibrium
Just ignore what I just said laughsbut if you have, the moral is just that, this is a really, really important relationship that is really helpful to remember. 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. This relationship is described by the following equation. This equation can be rearranged as follows. If the pH changes by 1 near the pKa value, the dissociation status of the acid changes by an extremely large amount.
When the pH is 3.
Predicting the pH of a Buffer
Conversely, to change the pH level near the pKa value of an acid, the dissociation status of the acid must be changed significantly, which requires using an extremely large amount of acid or base. The ability of a substance to maintain the pH of such solutions is referred to as its buffer capacity, where the closer the pKa and pH are, the higher the buffer capacity.
Therefore, when selecting a buffer solutionwhich are used widely in liquid chromatography, an acid or base buffer solution with a pKa value close to the target pH level is selected to maximize this buffer capacity.