Purity in chemistry refers to the extent to which a substance is free from impurities or contaminants. It indicates the proportion of the desired substance present in a mixture, and can impact properties such as melting point, boiling point, and reactivity. High purity substances are crucial for accurate experimental results, as impurities can interfere with chemical reactions and measurements. Purity is often expressed as a percentage, with pure substances being 100% free of impurities. Techniques such as chromatography and distillation are commonly used to analyze and achieve high levels of purity in chemical compounds.