Which of the following would you characterize as a pure or nearly pure substance?
a. baking powder
b. lemon juice
c. propane gas, used in outdoor gas grills
d. aluminum foil
e. ibuprofen
f. bourbon whiskey
g. helium gas
h. clear water pumped from a deep aquifer

Key Concepts

Pure Substances

A pure substance consists of only one type of particle, which can be either an element or a compound. Pure substances have consistent properties and composition throughout, making them distinct from mixtures. For example, elements like helium or compounds like water are considered pure substances, while mixtures like baking powder or lemon juice contain multiple components.

Mixtures

Mixtures are combinations of two or more substances that retain their individual properties and can be separated by physical means. They can be homogeneous (uniform composition) or heterogeneous (distinct phases). For instance, baking powder and lemon juice are mixtures, as they contain various ingredients that do not chemically bond together.

Chemical Composition

Chemical composition refers to the types and amounts of elements that make up a substance. Understanding the chemical composition helps in identifying whether a substance is pure or a mixture. For example, propane gas (C3H8) has a specific chemical formula indicating it is a pure compound, while substances like bourbon whiskey have complex compositions with various organic compounds.