Science, Tech, Math › Science Pure Substance Definition Share Flipboard Email Print ThoughtCo / Hilary Allison Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated January 12, 2019 In chemistry, a pure substance is a sample of matter with both definite and constant composition and distinct chemical properties. To avoid confusion, a pure substance is often referred to as a "chemical substance." Examples of Pure Substances Examples of pure substances include chemical elements and compounds. Alloys and other solutions may also be considered pure if they have a constant composition. WaterDiamondGoldTable salt (sodium chloride)EthanolBrassBronzeSaline solution Examples of Substances That Are Not Pure In general, any heterogeneous mixture is not a pure substance. If you can see differences in the composition of a material, it's impure, at least as far as chemistry is concerned. RocksOrangesWheatLight bulbsShoesSandwiches Common Definition of a Pure Substance To a non-chemist, a pure substance is anything composed of a single type of material. In other words, it is free of contaminants. So, in addition to elements, compounds, and alloys, a pure substance might include honey, even though it consists of many different types of molecules. If you add corn syrup to the honey, you no longer have pure honey. Pure alcohol could be ethanol, methanol, or a mixture of different alcohols, but as soon as you add water (which is not an alcohol), you no longer have a pure substance. Which Definition to Use For the most part, it does not matter which definition you use, but if you are asked to give examples of pure substances as part of a homework assignment, go with examples that meet the narrow chemical definition: gold, silver, water, salt, etc.