 So, what is volumetric analysis? Well, volumetric analysis I guess is easiest to contrast with gravimetric analysis, which is another method that we've used in order to determine the composition or the nature of particular types of mixtures in particular. The technique of volumetric analysis is what we apply to the solutions of different acids, bases or salts in order to determine something about their constituency. So, in simple terms, what we use volumetric analysis for is to determine the concentration of an unknown solution. So, that's pretty much what we're trying to do with pretty much the rest of this section of the acid and base reaction topic. So, in order to do that, the first thing we need is a standard and we talked about standards in the Year 11 course. A standard is a solution which has a known concentration and there are two ways to know a concentration. You can either use what we call a primary standard and a primary standard is a substance that has certain characteristics such as large molar mass, it's stable, it doesn't absorb moisture from the atmosphere and it remains consistent and pure over time. So, its concentration is not going to be constantly changing. One substance that's used very commonly in acid base titrations is sodium hydroxide. Now, sodium hydroxide does come in pellet form but its molar mass is just 40 and it's very, very unstable. The pellets themselves will absorb moisture from the atmosphere and this will change the concentration of the solution and continue to do so even after you've made the solution. So, this is not a primary standard but it could be standardized. That is, it could be a secondary standard and in fact often we will use a primary standard, often an organic acid such as tartaric, potassium hydrant phthalate or oxalic acid, something like that in order to standardize a solution of sodium hydroxide and then of course if we then use that solution to titrate against an unknown acid solution we will know the concentration of the sodium hydroxide and therefore we can calculate the concentration of the unknown. This is what volumetric analysis is all about and of course the most important thing about it is it's a precision technique and so therefore it requires practice. It's a precision technique and so whenever we're talking about precision techniques we need to look at accuracy, we need to look at reliability, are we getting consistent results in multiple repetitions and also validity. We need to make sure that what we're using is actually giving us the correct results and validity often relates to a very important component of a volumetric analysis which is the selection of an indicator. Now it's not a simple matter of just picking any old indicator and that will tell you what you need to know about your solutions. Different indicators can be used for different types of combinations of acids and bases and we'll explore that as we go further into this section of the module.