 All right, turning to the solubility of alcohols in water, it's again the polarity of the OH group that's important. If something is to be soluble in water, it must be able to bond favourably with water molecules. This either means the substance must be able to form hydrogen bonds, or it must be ionic, such that the ions can attract the partial charges on the water molecules. In the case of alcohols, there are two competing factors. The OH group can hydrogen bond, so this increases the solubility of alcohols in water. But they are still hydrocarbons, and the presence of a carbon chain in the molecule disrupts the hydrogen bonding of the water, which decreases their solubility. So the result of these competing factors is that short chain alcohols are completely soluble, or we say missable, since we're talking about two liquids mixing rather than a solid dissolving in a liquid. The short chain alcohols are completely missable in water. By short chain, I mean methanol, ethanol, propanol, so they've only got one, two, and three carbons in their carbon chain. This is because since the hydrocarbon chains are short, it's the polarity of the OH group that dominates the interactions with water. However, once we get up to butanol with a four carbon chain, the effect of that non-polar carbon chain begins to dominate, and the solubility decreases pretty quickly. So you can see that butanol has a solubility of 1.1 moles per litre. Then we add an extra carbon and get to pentanol, and it decreases down to 0.3 and so on. Now, I've written out a slightly more detailed description of how this solubility works here in red, so that you have a record of it, but you don't need to know this much detail for the exam. It's just if you're interested in understanding better how it works. You do need to know, however, and understand the black text on this slide. Incidentally, I think the last line of the red text is missing on this video, but if you go and look at the PowerPoint slides that are on the shared drive, you'll see there's just a few missing words at the end. Okay, so finally, there's the effectiveness of alcohols as solvents for other substances. So let's go through what we know about solvents in general. So the first solvent you met many years ago was water. It's the most polar solvent we know of. Its end to molecular forces are strongly dominated by hydrogen bonding, and it's used to dissolve other highly polar molecules or ionic substances. At the other end of the scale, we got alkanes, which are completely non-polar, because they can only interact with van der Waals forces. They cannot attract the molecules of a polar substance sufficiently to separate them from one another, and so they cannot dissolve them. They can only dissolve other non-polar substances. Okay, at intermediate polarity, we've got the halogenolkanes or haloalkanes. They interact using a combination of van der Waals forces and dipole-dipole attractions. So they are good solvents for a variety of molecules that are also of intermediate polarity. And this is where the alcohols fit in. They're similar to the haloalkanes in that they lie in between the two extremes of polarity, but they are able to form hydrogen bonds, which makes them better solvents for other molecules that can also hydrogen bond. Now, since most organic reactions take place in solution, the choice of solvent is crucial. It must dissolve the reactants, but it must not take part in the reaction. You must be able to remove it easily later without destroying the product, and ideally it should be low in toxicity, although that's not always possible. So an understanding of solvents is an important skill for an organic chemist.