Paper is not a chemical compound. Understanding the definitions of chemical compounds and mixtures clarifies its classification.
What Defines a Chemical Compound?
A chemical compound forms when two or more elements chemically bond together in fixed proportions. This chemical combination results in a new substance with properties often entirely different from its original constituent elements. For instance, water (H₂O) is a compound where two hydrogen atoms chemically join to one oxygen atom, forming a liquid with unique characteristics, unlike gaseous hydrogen or oxygen.
Compounds always possess a constant composition; the ratio of elements within them remains the same, regardless of how the compound was formed. For example, table salt (sodium chloride, NaCl) consistently has one sodium atom for every chlorine atom. Compounds cannot be separated into their individual elements through simple physical methods like filtration or distillation. Breaking down a compound requires a chemical reaction, which involves breaking existing bonds and forming new ones.
Understanding Mixtures
In contrast to compounds, a mixture consists of two or more substances physically combined rather than chemically bonded. The individual components within a mixture retain their original chemical identities and properties. For example, mixing sand and water creates a mixture where both the sand and water keep their distinct characteristics.
The proportions of substances in a mixture can vary widely. A mixture can have different amounts of its components. Components of a mixture can be separated by physical means, such as filtration, evaporation, or magnetic separation, because no new chemical bonds were formed. Mixtures are categorized into two types: homogeneous and heterogeneous. A homogeneous mixture appears uniform throughout, like salt dissolved in water, while a heterogeneous mixture has a non-uniform composition where individual components can often be visually distinguished, such as a salad or sand and water.
The Composition of Paper and Its Classification
Paper is primarily composed of cellulose fibers, a complex organic compound, but paper itself is not a single compound. Cellulose forms the main structural component, making up 90-99% of a paper product. These fibers are derived from plant sources, most commonly wood, and are long chains of carbon, hydrogen, and oxygen units.
Beyond cellulose, paper often includes other components like hemicellulose and lignin. Various additives are also incorporated during manufacturing to impart specific properties, such as sizing agents (like starch or rosin) to control ink absorption, and fillers (like calcium carbonate or clay) to improve opacity and smoothness. These components, including the cellulose fibers and additives, are physically intertwined and pressed together to form a sheet. They are not chemically bonded in fixed proportions to create a new, single chemical substance. Therefore, paper is classified as a heterogeneous mixture because its components retain their individual properties, are not uniformly distributed at a microscopic level, and their proportions can vary depending on the paper type.