Chemical Separation Techniques and Mixture Classification

Distillation: Separating Liquids by Boiling Point

Distillation is a separation process for components of a mixture that have different boiling points. The mixture is heated until it reaches the lower boiling point. One of the substances then becomes vapor and can be separated. This vapor is cooled until it condenses and is collected in a vessel.

Crystallization: Forming Pure Solid Crystals

Crystallization is the process of forming solid crystals from a liquid solution, typically by evaporating the solvent. When all the liquid has evaporated, the solid crystals remain at the bottom of the vessel.

Paper Chromatography: Separating Organic Substances

Paper chromatography is used to separate several organic substances that travel through the chromatography paper at different speeds. A small amount of the mixture is placed at the bottom of a paper strip in contact with an organic solvent. The polar substances within the mixture bind more tightly to the paper, causing them to travel a shorter distance through the paper strip.

Understanding Solutions and Mixture Types

The term solutions refers to homogeneous liquid mixtures. Generally speaking, solutions are formed by two components: solute and solvent. The solute is the component present in the lesser amount, whereas the solvent is the component found in the greater amount. Sometimes, the distinction between homogeneous and heterogeneous mixtures is not always obvious. In fact, it depends on the size of the particles and the separation method used to isolate their components.

Distinguishing Mixture Types: Suspensions, Colloids, and Solutions

Generally speaking, we can distinguish between suspensions, colloids, and actual solutions:

• A suspension is a mixture with large particles, whose size is greater than 1 μm, making them visible to the naked eye. Suspensions are heterogeneous mixtures that can be filtered or decanted and eventually settle. Examples include a mixture of fine sand in water or dust particles floating in the air.
• Colloids are heterogeneous mixtures whose particle sizes are between 1 and 1000 nm. They cannot be completely separated by filtering, although some particles may be retained in the filter. Their particles can be detected by the scattering of light when it passes through the mixture; this property is called the Tyndall effect. Examples of colloids include milk or some juices.
• Finally, actual solutions have particles whose size is similar to atoms or molecules, less than 1 nm. They cannot be filtered or decanted and do not show the Tyndall effect.

Concentration and Solubility: Defining Solution Composition

The composition of a solution refers to the relative amount of solute in the mixture. Solutions can be prepared according to a chosen proportion, meaning they have variable composition. The properties of a solution depend directly on its composition. Consequently, to accurately describe a solution, we must know its components and its precise composition.