Physical Properties: The Starting Point

Physical properties can often be measured without altering a substance’s chemical identity, making them a natural first step in characterization:

• Melting and boiling points — sharp, well-defined transition points that serve as a quick purity check, since impurities typically broaden or shift these values

• Density — mass per unit volume, useful for identifying substances and detecting contamination or concentration changes

• Solubility — how a substance behaves in different solvents, which informs everything from purification methods to drug formulation

 • Refractive index — how light bends passing through a substance, a fast, non-destructive way to check purity in liquids

Chemical Properties: How a Substance Reacts

Where physical properties describe what a substance is, chemical properties describe what it does:

• Reactivity — how readily a substance participates in chemical reactions, including with common reagents like acids, bases, or oxidizers

• pH and acidity/basicity — measured with pH meters or indicator methods, central to everything from environmental testing to biochemistry

• Oxidation states — determined through titration or electrochemical methods, important for understanding redox behavior

 • Stability — how a substance behaves under heat, light, or prolonged storage, often measured through accelerated aging studies

Thermal Analysis

Thermal properties reveal how a substance responds to changing temperature, which matters for both characterization and practical handling:

• Differential Scanning Calorimetry (DSC) measures heat flow into or out of a sample, detecting melting points, crystallization, and phase transitions

 • Thermogravimetric Analysis (TGA) tracks weight changes as a sample heats, revealing decomposition points or trapped solvent and moisture content

Spectroscopic Measurement

Spectroscopy measures how a substance interacts with light or radiation, translating that interaction into structural and compositional information:

• UV-Vis measures absorbance, useful for concentration and certain structural features

• IR spectroscopy identifies functional groups through vibrational absorption

• NMR reveals detailed atomic connectivity

 • Each technique measures a different physical interaction, which is why combining them gives a far more complete property profile than any single method alone

Measuring Concentration and Purity

Determining how much of a substance is present, and how pure it is, relies on a mix of techniques: chromatography separates a mixture into components and quantifies each by peak area, while titration determines concentration through a controlled chemical reaction with a known reagent. Elemental analysis compares measured atomic ratios against theoretical values to confirm both identity and purity.

Why Precision Matters Here

Chemical property measurements often feed directly into decisions with real consequences a drug’s stability profile determines its shelf life, a material’s melting point determines its manufacturing process, a compound’s reactivity determines how it must be safely stored and transported. An imprecise measurement doesn’t just create an inaccurate data point; it can lead to a product that fails in the field or a hazard that wasn’t anticipated.