Quantitative analysis is applied to a sample known to contain an atom or compound, but the concentration or amount is unknown. There are two key types of analytical chemistry that are quantitative: volumetric and gravimetric. Volumetric analysis is done primarily through titrations of a standard solution into the sample with an indicator (usually involving a color change) to determine the concentration of the sample. This is commonly used for pH testing as many common indicators are pH sensitive.
Gravimetric analysis involves weight in order to reverse engineer the amount. An example of this is applying an excess of a standard solution into a known volume of a sample solution in order to precipitate out a solid. The solid is then filtered and dried so that it may be weighted in order to calculate the moles of ions in the solution. Another example of gravimetric analysis is using dehydration to calculate the percentage of water in a compound. By taking the weight before and after placing a hydrated compound in an oven to dry, a ratio of weights can determine the percentage of water and the molecule makeup.