Analytical Chemistry Overview

Study Notes

Analytical chemistry is the science of characterizing and measuring chemicals, including separating, identifying, and determining the relative amounts of components in a sample.
Chemical analysis is categorized into two types: qualitative and quantitative analysis.

Qualitative analysis determines the chemical identity of species within a sample.

Quantitative analysis establishes the relative amounts of one or more species (analytes) in a sample numerically.
- Gravimetric Analysis: Determines the mass of the analyte (sample).
- Volumetric Analysis: Measures the volume of a solution required for complete reaction with the analyte.
- Instrumental Analysis: Measures optical, electrical, or thermal properties.

Gravimetric analysis is the most accurate analytical technique and is an absolute method.
It involves precise methods for macro-quantitative analysis, and possible errors are verifiable.
Precipitation Gravimetry: An insoluble compound forms when a precipitating reagent (precipitant) is added to a solution containing the analyte. Any reaction creating a precipitate can be used.
Most precipitation gravimetric methods developed in the 19th century were for ore analysis.
For accurate results, a precipitate's solubility must be minimal. The accuracy of the techniques is typically better than ±0.1%, meaning the precipitate accounts for at least 99.9% of the analyte.
Solubility losses can be minimized by controlling precipitate formation conditions. Accounting for all equilibrium reactions affecting the solubility is crucial.
For example, to determine silver gravimetrically, adding NaCl forms AgCl precipitate. The solubility, S, of the precipitate relates to the solubility product (Ksp) and the chloride ion concentration. Increasing the Cl⁻ concentration increases AgCl solubility.

Gravimetric analysis calculations use the formal weight of the analyte and precipitate, along with the amount of analyte per mole to determine the gravimetric factor (Gf). This allows the calculation of the analyte's percentage in a sample from the experimentally known weight of the precipitate.

Volume: Solution volume during precipitation needs adjusting to a low solubility condition. Excessive volume leads to precipitate coagulation.
pH: Influences the solubility of the analytical precipitate and can cause interference from other substances.
Temperature: Higher temperatures increase precipitate solubility, which can make filtration difficult.

Various elements and compounds can be precipitated by specific reagents to allow their determination.
8-hydroxyquinoline, for instance, is a precipitating agent used to determine several elements, such as Aluminum, where pH 4 condition is ideal and magnesium necessitates a higher pH.

Volumetric analysis, also known as titration, is used to determine unknown reactant concentrations.
A reagent with a known concentration (titrant) is used to react with a solution of unknown concentration (analyte). The volume of titrant is measured precisely to determine analyte concentration.
Titration involves accurately measuring the volume of titrant solution required for complete reaction with the analyte. Key terms relate to this are the equivalence point and the endpoint.

The equivalence point is the theoretical point where the added titrant is equivalent to the analyte in terms of moles.
The endpoint is where an indicator, signaling complete reaction, reveals the observed color change . End point occurs after the equivalence point.

Various indicators and measuring tools exist to reveal the endpoint, including color changes from specific reactions, such as those with redox titrations, as well as indicators that operate by measured conductivity or pH changes.