https://www.khanacademy.org/science/grade-7-science-cambridge-curriculum/x754b285620daf71e:mixtures-and-impurities/x754b285620daf71e:purity-of-a-substance/e/purity-of-a-substance 2026-07-15T08:30:45.200943224Z Purity of a substance This exercise reinforces core chemistry concepts by challenging students to classify matter into elements, compounds, and mixtures based on molecular purity. It develops quantitative fluency through percentage purity calculations of commercial metal alloys and trace gemstone lattice impurities. Finally, it builds analytical skills by requiring students to interpret complex mixture distributions and predict the purity profiles of chemical reaction products. Asma Rouf exercise