Seawater is classified as a mixture rather than a pure substance. This is because it contains a variety of different components, including water, salts, minerals, and organic matter. While pure water is made up solely of H2O molecules, seawater’s composition varies greatly depending on its location and depth.
The main constituents of seawater are dissolved salts, primarily sodium chloride (common salt), but there are also other salts like magnesium sulfate, calcium carbonate, and potassium chloride. Alongside these, it contains trace elements and a variety of dissolved gases such as oxygen and carbon dioxide, making it a complex solution. This mixture does not have a uniform composition, which is characteristic of mixtures.
In contrast, a pure substance has a consistent and definite composition, with distinct chemical properties. For example, distilled water is a pure substance because it contains only water molecules. In summary, seawater is a mixture due to its diverse and varying components, and the presence of multiple substances distinguishes it from pure materials.