* Mixtures: Coffee is a complex mixture of many different compounds. It contains:

* Caffeine: The stimulant that gives coffee its "kick"

* Water: The main component, extracted from the beans during brewing

* Organic acids: Like chlorogenic acid, which contributes to flavor and bitterness

* Sugars: Natural sugars present in the beans, providing sweetness

* Volatile oils: Responsible for the aroma of coffee

* Other compounds: Like tannins, proteins, and minerals

* Variable Composition: The exact composition of coffee varies depending on:

* Bean variety: Different beans have different chemical profiles

* Roasting process: Roasting affects the breakdown of compounds, influencing flavor

* Brewing method: Different methods extract different amounts of compounds

Pure substances have a fixed and definite chemical composition. They are made up of only one type of atom or molecule. Examples include water (H₂O), gold (Au), and table salt (NaCl). Coffee, on the other hand, is a combination of many different molecules, making it a mixture.