 Now that we've had a chance to get our heads around the fact that not all acids are strong acids Some of them are weak and do not fully dissociate. We need to start looking at how we can quantify that we can work out unknown concentrations using the technique of Titration but in order for us to get a bit of more of a handle on exactly what's happening Mathematically for different types of acids. We need this mathematical relationship in order to identify it the fact that Weak acids do not fully dissociate Creates an equilibrium and we know how to deal with equilibrium situations if you want to Write this in perhaps a little bit more Precise detail then we should actually include water in our Equation and therefore the h3o plus which is aqueous and the anion which is Left in the solution as well So this is the dissociation that occur or the ionization that occurs when the proton from the acid is donated to the at the water molecules in order to form the hydronium ion and the anion now as with our previous calculations of the equilibrium constant which was products over reactants if we were to look at the products here which go on the numerator and The reactants down the bottom if I was to put the water in there, which I added in the last In the second of these equations the problem with water is that the value of the concentration of water in liquid is Irrelevant and it we just treat it as a constant and therefore it disappears And that's often why you find the first of these Often written in order to help us understand the value of the equilibrium constant as it applies to acid ionization Just because we remove that water from the equation Obviously when we're doing the calculations, whether we're thinking about the hydronium ion or the hydrogen ion Concentration these two things are interchangeable and therefore can both be used Irrespective of how we represent them in the equation The important thing about this type of an equilibrium constant is this is called the acid ionization constant Now obviously because it is products over reactants the stronger the acid the greater degree of of ionization and That's another way of saying the greater the number of products and therefore They're higher the value of k a said k is the equilibrium constant And we use the subscript a to indicate acid to k a is the acid ionization constant So what can we do with that? Well, one of the things that we can do with that is we can also draw a Relationship to what we call the p k a so we've we know that the concentration of Hydrogen ions can be related to the pH scale It's a log scale and and it gives us a way of measuring Differences in the values for each of these if we identify that the k a value is often a value That's related directly to that A hydrogen or hydronium ion concentration then we can also look at a scale which we call the p k a scale So this is another one of these little equations that is worth remembering and we'll have a look at a couple of examples for you in order to practice with it of course the problem with the the p k a value is like the value for the pH as the acid gets weaker the p k a increases so we know for example that pH of one is going to be a stronger acid solution than a pH of two and this scale works the same for the p k a's so a p k a view which is small or low Is going to be stronger Than a high p k a the alternate to that is as the acid gets weaker the p k a increases So have a look at the relationship between k a and p k a to give you an idea of how these things can actually be used to Determine the relative strength of an acid solution Of course there's a there's an equivalent for bases which we call the k b or the p k b And they are calculated in exactly the same way and we'll probably have a look at a couple of examples in class Just to mention it. So you've seen it in passing rather than spend too much time today