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Annabel Lapuz Carungin,MD, RMT, PT, RN, RM, MAN
VOLUMETRIC ANALYSIS It is a general term for a method in quantitative chemical
analysis in which the amount of a substance is determined by the measurement of the volume that the substance occupies.
It is commonly used to determine the unknown concentration of a known reactant.
Volumetric analysis is often referred to as titration, a laboratory technique in which one substance of known concentration and volume is used to react with another substance of unknown concentration.
Volumetric analysis was first introduced by Jean Baptiste Andre Dumas, a French chemist.
He used it to determine the proportion of nitrogen combined with other elements in organic compounds.
Dumas burned a sample of a compound with known weight in a furnace under conditions that ensured the conversion of all nitrogen into elemental nitrogen gas or N2.
In Dumas' experiment, the nitrogen from the furnace was then carried in a stream of carbon dioxide and passed into a strong alkali solution.
The solution absorbed the carbon dioxide and allowed the nitrogen to accumulate in the tube.
The mass of the nitrogen was then calculated from the volume that it occupied under the known conditions of pressure and temperature.
As a result, the proportion of nitrogen in the sample was determined.
It is the process of obtaining quantitative information from a given sample, according to the University of Waterloo, that involves a fast chemical reaction.
When the reaction involves an acid and a base, the method is referred to as an acid-base titration.
When the reaction involves oxidation and reduction, the method is referred to as a redox titration.
Volumetric analysis is used in high school and college chemistry labs to determine concentrations of unknown substances.
The titrant (the known solution) is added to a known quantity of analyte (unknown solution) and a reaction takes place. Knowing the volume of the titrant allows the student to determine the concentration of the unknown substance.
Medical labs and hospitals use automated titration equipment for basically the same purpose.
Examples Volumetric analysis and titration are used by the
biodiesel industry to determine the acidity of a sample of vegetable oil. By knowing the precise amount of base that is needed to
neutralize a sample of vegetable oil, scientists know how much base to add to neutralize the entire amount.
Titration has similar uses in petrochemical and food industries. For example, an acid-titration may be used to determine free
fatty acid content of an oil; a redox titration may be used to determine the amount of unsaturated fatty acids.
Glass apparatus used to measure the volume of a liquid or gas is called volumetric glassware.
Examples: pipetsvolumetric flasksburets
Three types of containers used in lab to contain or deliver liquids:
1. Volumetric glasswareAre containers that have been calibrated at a
specific temperature to deliver or contain VERY PRECISE amounts of liquid.
2. Ordinary glassware Has less precise volume calibrations and are
used whenever the volumes do not have to be measured as accurately.
3. Disposable glasswareIt is used to transfer or hold liquids
temporarily and may not contain any volume markings.
Volumetric glassware :
volumetric flasks Ordinary glassware:
graduated cylinders Disposable glassware (or plastic ware)
How to read the level of liquid in glassware:
• The “meniscus” of a liquid refers to the curvature of the liquid surface in a narrow container.
• If the surface of the liquid is concave (as in water), the liquid level is measured using the bottom of the meniscus.
• If the surface is convex (upward curving) as in mercury, the liquid level is read from the top of the meniscus.
• It is important to position the eye at the same level as the meniscus to avoid a parallax error.
Care of glassware: Glassware should be washed with a mild soap solution,
rinsed with tap water, and then rinsed with distilled water. If beads of water stick to the inside walls, it be should be cleaned again.
If glassware is to be dried, allow it to drain or use paper towels. NEVER SLING GLASSWARE TO REMOVE WATER.
NEVER TAP GLASSWARE AGAINST THE SIDE OF THE SINK.
A buret or pipet should be rinsed with a small amount of the solution to be used to remove any water droplets from the glass walls.
Burets: Burets must be read to the hundredths of a milliliter.
Note that the liquid level markings begin at the top or open end. This is because the buret is designed to deliver liquids.
All volumes are measured as the DIFFERENCE between an initial and final reading.
Changes affecting the orifice will affect reproducibility; a buret with a chipped or fire-polished tip should not be employed for accurate work. Drainage errors are usually minimized if the tip is constricted so that the meniscus falls at a rate not exceeding 0.5 cm/sec.
Volumetric flasks are designed to contain a specified volume of liquid.
Rather than technique, the principal source of error is variation in temperature, which causes enough expansion or contraction of aqueous solutions to give errors on the order of 0.1% per 5 degrees C.
Volumetric pipets are used to deliver precisely a single, definite volume of liquid.
The tip must meet stringent requirements because drainage time is controlled by the diameter of the tip.
The amount of liquid delivered depends on how a pipet is used; accuracies of 1 part per 1000 can be attained readily, provided the pipets are used in a reproducible manner.
Burets Burets are designed to accurately deliver measurable
volumes of liquid, particularly for titrations.
A 50-mL buret, the most common size, has 0.1-mL graduations along its length and can be read by interpolation to the nearest 0.01 mL.
Changes affecting the orifice will affect reproducibility; a buret with a chipped or fire-polished tip should not be employed for accurate work.
Drainage errors are usually minimized if the tip is constricted so that the meniscus falls at a rate not exceeding 0.5 cm/sec.