Glossary
Distillation
A separation technique used to separate components of a liquid mixture based on differences in their boiling points.
Example:
To purify water, it can undergo distillation, where water evaporates and then condenses, leaving impurities behind.
Filtration
A separation technique that separates insoluble solid particles from a liquid or gas by passing the mixture through a filter medium.
Example:
When brewing coffee, the coffee grounds are separated from the liquid coffee by filtration.
Formula Units
The empirical formula of an ionic or covalent compound representing the simplest ratio of ions or atoms. In mixtures, different types of formula units or molecules are present.
Example:
In a solution of salt water, both H₂O molecules and NaCl formula units are present.
Heterogeneous Mixture
A mixture in which the components are not uniformly distributed and can be visibly distinguished as separate phases.
Example:
A bowl of cereal with milk is a heterogeneous mixture because you can clearly see the individual cereal pieces and the milk.
Homogeneous Mixture
A mixture in which the components are uniformly distributed throughout and appear as a single phase, making individual components indistinguishable.
Example:
A perfectly mixed cup of coffee is a homogeneous mixture because you cannot distinguish the coffee from the water or sugar.
Matter
Anything that has mass and occupies space. It exists in various states and can be classified by its composition.
Example:
The air we breathe and the water we drink are both forms of matter.
Mixture
A material system made up of two or more different substances that are physically combined but not chemically bonded.
Example:
Lemonade is a mixture of water, lemon juice, and sugar, which can be combined in varying proportions.
Mobile Phase
The solvent that moves through the stationary phase in chromatography, carrying the components of the mixture at different rates.
Example:
The solvent used to develop a TLC plate, such as hexane or ethyl acetate, is the mobile phase.
Polarity
A property of a molecule describing the uneven distribution of electron density, leading to partial positive and negative charges, which influences solubility and intermolecular forces.
Example:
Water is a polar molecule, which is why it can dissolve many ionic compounds and other polar substances.
Pure Substance
A form of matter that has a uniform and definite composition, consisting of only one type of atom or molecule.
Example:
A sample of pure gold (Au) is a pure substance because it consists only of gold atoms.
Retention Factor (Rf)
A ratio in chromatography that quantifies the distance a component travels relative to the distance the solvent front travels, used to identify substances.
Example:
An Rf value of 0.5 means a compound traveled half the distance of the solvent front on a TLC plate.
Stationary Phase
The immobile phase in chromatography, typically a solid adsorbent material coated on a plate, which selectively interacts with components of the mixture.
Example:
In TLC, the silica gel on the plate acts as the stationary phase, attracting more polar compounds.
Thin-Layer Chromatography (TLC)
A chromatographic technique used to separate non-volatile mixtures based on differences in polarity and differential partitioning between a stationary phase and a mobile phase.
Example:
Forensic scientists might use Thin-Layer Chromatography to separate and identify components of ink from a ransom note.