So in our previous lesson video, we talked about the acid dissociation constant, or the K A, which we know is a quantitative measure of the strength of an acid. And the greater the K A value is, the stronger the acid will be. But the thing about the K A values is that sometimes they are inconveniently large or small numbers that need to be expressed with scientific notation because of how large and small they could be. And that can make calculations unnecessarily mawr complicated. But the good thing is, is that the K A values can be expressed on a longer rhythmic scale with PK A values. And so the PK A values are also a quantitative measure of the strength of an acid, just like the K A. Value is, however, the relationship is different. And so again, recall with the K A values, the greater the K a, the stronger the acid. But with the PK, it's different. And so the greater the PKK, the weaker the acid is, and so it's actually an inverse relationship. And so, in our example, down below, we have an equation for the P K A. And just like from our previous lesson of pH. We know that the P here is really just representing the negative log. And so the P K is just the negative log of the K A value. And that's exactly what we have over here. The negative log of the K A. Now the rules of logarithms say that the negative log is equal to the positive log of the reciprocal. So we have both equations shown here, just in case your professors leaning one way or the other. So now we'll be able to get a little bit of practice utilizing this equation as we take a look at our chart over here on the right, which has an example of a weak acid of acetic acid, and this yellow column and an example of a strong acid HDL or hydrochloric acid in the Blue column, and were given the K A values for both of these acids and noticed that the K a value of the weak acid is an incredibly incredibly small. And we know that it's small because it's expressed in scientific notation with a negative exponents, and the strong acid, on the other hand over here, has an incredibly large K a value. And again we know it's large because it's expressed in scientific notation with a positive exponent. And so these numbers that are inconveniently large and small again can be unnecessarily over complicating calculations. But we can pretty easily convert them into PK a values. And so we can use this equation over here for the PKK. And so, for the PKK, we know that we can take just the negative log of the K A values. So for the weak acid, it will be the negative log of 1.76 times 10 to the negative fifth, which is equal to 4.76 So that's the PK for the weak acid. And then, if we do the same for the strong acid over here, essentially we'll take the negative log of the K A, which is 1.3 times 10 to the sixth, and that is equal to negative 6.3. And this is the PKK for the strong acid. And so what you'll notice is that the PKK for the weak ass is actually larger, then the PKK for the strong acid. And so that's because again it's an inverse relationship. The greater the PK, the weaker the acid is, and so moving forward, we'll be able to get a little bit of practice utilizing these concepts, so I'll see you guys in those videos.
