Choose the pure substance from the list below. osea water sugar air lemonade milk Question 2 (1 point) Saved A chemical change O occurs when methane gas is burned. occurs when paper is shredded. occurs when water is vaporized. occurs when salt is dissolved in water. occurs when powdered lemonade is stirred into water.

Pure substances have definite constant compositions (reflected in formulas) and have their own chemical properties. On the other hand, mixtures are made of two or more pure substances (variable composition) and their chemical properties depend on each combination. From the list, only sugar is a pure substance (C₁₂H₂₂O₁₁), whereas seawater, air, lemonade, and milk are mixtures.

Chemical changes (chemical reactions) occur when pure substances transform into others, and therefore there are new formulas. Conversely, in physical changes, pure substances preserve their identity (formula) but have changes in their physical properties. Methane being burned is a chemical change since new substances are formed:

CH₄ + O₂ ⇄ CO₂ + H₂O

Water vaporization, paper shredding and dissolution of solids in liquids are examples of physical changes.