 Now that you have been introduced to coordination compounds, let's quickly discuss an important topic here that students usually get confused with, which is double salt versus coordination compounds. And in this video, we will see what these two are and how exactly they are different from each other. Both double salts and coordination compounds are actually addition compounds. That is, they both are formed when stoichiometric amounts of two or more stable compounds join together. For example, when k-sale, mgCl2 and water are mixed together, we get carnalite which is widely used in fertilizers. Here we have potash alum which is again widely used in medicines and also in water purification processes. Both these are examples of double salts. On the other hand, here we have a typical coordination compound, which is potassium ferrocyanate. The familiar format of this would be K4, Fe, CN6. Now the difference between a double salt and a coordination compound is that double salts are those that lose their identity in solutions, whereas coordination compounds retain their identity in solutions. What do I mean by that? When crystals of carnalite are dissolved in water, the resulting solution exhibits properties of potassium, magnesium as well as chloride ions. Similarly, potash alum in solution shows properties of potassium, aluminium as well as sulphate ions. As we know, both these are double salts and they exist only in crystalline state and completely dissociate into simple ions in solutions, which is why we say that they lose their identity in solutions. On the other hand, coordination compounds like potassium ferrocyanate and tetramine copper sulphate monohydrate do not form simple ions or show properties of let's say copper or iron or cyanide ions in their solutions. Instead, their complexes remain completely intact. Whereas, Cupra ammonium ion and ferrocyanate ion exist as distinct entities both in solid as well as in their solutions. Now it's especially important to understand the behaviour of these ions in solutions because we know that the chemistry of metal ions in their solutions is essentially the chemistry of their complexes and transition metal ions form plenty of stable complexes. In a solution, a free metal ion is usually coordinated either with water molecules or with other ligands. For example, copper ions exist as a pale blue complex CuH2O62 plus in aqua solutions as well as in hydrated crystalline solids. And if we add ammonia to the solution, then the pale blue colour transitions to deep blue colour corresponding to the formation of Cupra ammonium ions as shown here. Here we can see that ammonia replaces the water molecules. Now why does this happen? Why ammonia replaces water is something that we will discuss in the upcoming videos.