The purpose of melting and boiling points in a lab experiment is to use them to help identifiy unknown substances. By taking a melting point of an unknown solid, you can compare it to a list of potential solids and their melting points and make a match to identify the solid. Likewise, you can take a boiling point of an unknown liquid and compare it to other boiling points to make a match and identify the liquid. Another purpose of a melting point experiment is to use the melting point range of a substance to help determine its general purity. The smaller the melting point range, the more pure the substance is. The larger the melting point range, the less pure the substance is.