Hanna Instruments HI 904, Быстрый старт

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5
TITRATION THEORY
1 GENERAL REVIEW OF TITRATION THEORY
1.1 Introduction to Titrations
A titration is a quantitative, volumetric procedure used in analytical chemistry to determine
the concentration of an analyte (the species being measured) in solution. The concentration
of the analyte is determined by slowly adding a titrant (reagent) to the solution. As the titrant
is added, a chemical reaction occurs between the titrant and the analyte.
Titration reactions are relatively fast, simple reactions that can be expressed using a chemical
equation. The titration reaction continues as the titrant is added until all of the analyte is
consumed and the analyte reacts completely and quantitatively with the titrant.
The point at which all of the analyte has been reacted is called the equivalence point, also
known as the theoretical or stoichiometric endpoint. This point is accompanied by an abrupt
physical change in the solution, which sharply defines the endpoint of the reaction. The
physical change associated with the titration endpoint can be produced by the titrant or an
indicator and can be detected either visually or by some other physical measurement.
Titrations cannot be used to determine the quantity of all analytes. The chemical reaction
between the titrant and analyte must fulfill four requirements:
• The reaction must be fast and occur within approximately one second after the
titrant is added;
• The reaction must go to completion;
• The reaction must have well-known stoichiometry (reaction ratios);
• A convenient endpoint or inflection point.
Titrations are highly precise and can provide many advantages over alternative methods.
Titrations are quickly performed and require relatively simple apparatus and instrumentation.
1.2 Uses of Titrations
Titrations can be used in many applications, including:
• Acid content of plant effluents, food (i.e. cheese and wine), plating and etching
baths, petroleum products, drugs;
• Base content of fertilizer (containing ammonia), bleach, minerals;
• Hardness in water;
• Metal content of alloys, minerals, ores, clays, waters, plating baths, paints,
paper, plant materials, biological fluids, petroleum products;
• Moisture content in butter, dairy cream, food grade oil, honey, margarine,
mayonnaise, milk, powdered milk, sugar;
• Redox reagent concentrations such as available chlorine in potable water,
peroxide, traces of oxidants and reductants in food, reductants in high
temperature or high pressure boiler water, vitamin analysis.