 In this video, we'll look at characteristic chemical reactions that mark out acids. So let's begin by revising our comparison of the properties of acids and bases. Acids taste sour, whereas bases taste bitter. Acid base indicators will change colour depending on which type of chemical they come into contact with, the classic example being litmus, which turns red in an acid and blue in a base. Acids and bases also, if they're mixed, neutralise each other's properties and they can corrode materials, although the chemical reactions that occur during the corrosion are different for acids and bases. So we're going to look specifically at some of these characteristic reactions that acids undergo. So here are those reactions. I've written them out here in a generic form. I'm not going to specify what acid or what base or what metal or what carbonate at this point. The point is that as long as you know what class of substance is reacting, the reaction will always follow the same general form. The neat thing about this is that once you choose what your reactants are going to be, you can predict what the products of the reactions will be. So these are our reactions. Let me introduce them to you first, and then I'll go through and give examples. The first is dissociation. Here an acid molecule that's dissolved in water splits up, and when it does so, the result is one or more protons and whatever the remaining anion is. Remember that the protons or hydrogen ions can also join up with water to form hydronium ions. The next is a neutralisation reaction. When an acid reacts with a base, the result is a salt, an ionic compound and water. The next two reactions are kinds of corrosion. When an acid reacts with a metal, the metal is eaten away and the products are a salt and hydrogen gas. When an acid reacts with a carbonate, the carbonate is eaten away and a salt and carbon dioxide gas and water are produced. Before I go into examples, I just want to remind you of Bronsted's and Lowry's definitions of acids and bases, because we'll look at each of the reaction examples in the context of these definitions. Remember that an acid is a chemical that when it reacts, it donates a proton or a hydrogen ion to something else. That is, it will lose a proton itself. Bases are the opposite, something that accepts a proton during a chemical reaction.