 In this module, we will discuss about classical analytical methods. Nowadays, there are many instrumental techniques available, but at the same time, classical analytical methods are still in use. Acid-based titration, redox titrations, complexometric titrations, and gravimetric analysis are some of these methods. The main requirement of instrumental techniques is that we can make it more effective. We can also know about very little concentration and light. But the places where it can still be used, we take support of acid-based titrations or redox titrations. The reason for this is that these are cheap techniques and are not expensive. And compared to instrumental techniques, where they can be used, it is definitely performed there. In USP, BP, i.e. British Pharmacopoeia, aspirin is a common drug that we use as a painkiller. For this, the acid-based titrations are also present at this time. Although most of the analytical methods are now available on HPLC, but for this basic drug, the acid-based titrations are performed only with acid-based titrations. Complexometric titrations, in which we make complexes with ligands. And this technique is mostly used if in light our metal ions, calcium, magnesium, or other metal are present. Redox titration, the basic technique where reduction is being oxidized. Because of this, we observe color change. Redox, to play a lot of functions in our body, the products that can oxidize are beneficial to us. For example, you hear advertisements about tea leaves that they have anti-oxidant, which are beneficial to us. So, for this evaluation, we use a lot of things like redox titrations. Such as gravimetric analysis, where the precipitate can be out, to find out the concentration of any analyte, we use gravimetric analysis. Acid-based titrations, this is our first technique that we will discuss here. Chemical equilibrium, a small equation is written in front of you, that A plus B gives us C plus D, or X plus Y. This is a reversible reaction, that is, your reactant is converting into a product, the product is converting into a reactant. It takes some time to come to this reaction on equilibrium. And on equilibrium, the way we take out its equilibrium constant, which we have discussed in our primary classes in matriculation, that K is equal to concentration of X and Y, multiply product of X and Y divided by product of A and B. That is, product key concentration divided by reactant concentration is our K equilibrium constant. In acid-based titrations, the equilibrium constant is not established. Acid-based acids will direct the foreign bases and after titrating, they will make salts and water. But water itself, H2O, if there is no electrolyte in it, then we can consider that it is present in an equilibrium position with its ions. H2O gives us H positive ion and OH negative ion. Different theories can be discussed, in which acids and bases are defined, from which Arrhenius theory, Bronsted, Lawry Bronsted theory is called and Lewis theory. First of all, Arrhenius described this and he gave an understanding. But before this, it was necessary to use acids and bases. A Muslim scientist also worked in his era to make acids. And before this, some classical theories were also present. In some understanding, the compounds that keep oxygen are called acids. Or in acids, oxygen is definitely present. Or in some cases, they are correlated with their taste. Or in other cases, they are correlated with their taste. So Arrhenius first of all, scientifically, when we read the notations, that we replace all the products that are H positive ion, we will call them acids. And we will call the hydroxyl ion, which is negative ion, as the bases. In this theory, some loopholes are present. They are not able to explain that ammonia, which does not have hydroxyl ion, but it shows basic character. So Lawry Bronsted theory explains this. That all the things that give H positive ion, we will call them acids. And we will call the H positive ion, except it. And in this form, he explained to Ammonia that why it is a base. Because after taking H positive ion, it becomes ammonium. Now here, water. Is this acid or base? So we can understand that water is amphoteric. This is acidic and basic. H2O accepts H positive ion and becomes hydronium. And hydroxyl ion also replaces it. That is why it has basic character. So we can see its conjugate bases and assume that water has amphoteric properties. Acidic and bases are also present. Livis, who defined Octatrugl, explained this in another way. That all the things that donate to the electron will be called bases. And those who accept will call them acids. And according to this theory, the first things that Lawry Bronsted considered bases, or what Arhenis had considered before, all those things also sustain their place. Ammonia, because the electron is donating, it is a base. At this time, there is another notation in front of you. Water's dissociation constant is written. This is HOH negative H positive ion concentration. And the reactant or starting material is H2O. The concentration of water remains constant. And if we take this to the other side of the equation, it is called ionic product of water. Calculated is that the dissociation constant of water is very low. E1 multiplied by 10 to the power of minus 4 moles square decimetre cube. Cubes square. If we want to take out the concentration of H positive ion in acidic solutions, then mainly H positive ion concentration, if we make a solution of HCl, 1 gram, 1 mole per decimetre cube, then the main concentration will be present in only H cubes. pH is called a negative log of hydrogen ion concentration. And to take it out, we commonly use pH at this time to know the hydrogen ion concentration. pH meters are available. Acid-based titations are also done with indicators. Acid-based titations are also potentially metric, where we use this pH meter of any product. We observe the change in pH and we know the end point on its basis.