Most, but not all, chemicals are labeled with a grade. The grade indicates how pure the chemical is. The greater the quantity of other chemicals, metals, water, or other impurities in the chemical, the lower the grade. There are many different grading standards, but the three you are most likely to encounter are: reagent grade, laboratory grade, and technical grade. Of these, reagent grade is the most pure and technical grade is the least pure. See the table below for more details. Manufacturing pure chemicals can be time-consuming and expensive; for this reason, higher-grade chemicals cost more than lower-grade chemicals. For the purposes of most science fair projects, laboratory- or technical-grade chemicals are of sufficient purity. When in doubt, purchase laboratory-grade. If a Science Buddies project requires reagent-grade chemicals this will always be specifically stated in the Materials and Equipment section of the project. If you are ordering chemicals from an online distributor and do not know which grade to purchase, consult the customer-service representative or your chemistry teacher.