In
analytical chemistry
Analytical chemistry studies and uses instruments and methods to separate, identify, and quantify matter. In practice, separation, identification or quantification may constitute the entire analysis or be combined with another method. Separati ...
, a standard solution is a
solution containing a precisely known
concentration
In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', ''molar concentration'', '' number concentration'', ...
of an element or a substance. A known mass of solute is dissolved to make a specific volume. It is prepared using a standard substance, such as a
primary standard A primary standard in metrology is a standard that is sufficiently accurate such that it is not calibrated by or subordinate to other standards. Primary standards are defined via other quantities like length, mass and time. Primary standards are ...
. Standard solutions are used to determine the concentrations of other substances, such as solutions in
titration
Titration (also known as titrimetry and volumetric analysis) is a common laboratory method of quantitative chemical analysis to determine the concentration of an identified analyte (a substance to be analyzed). A reagent, termed the ''titrant'' ...
. The concentrations of standard solutions are normally expressed in units of
moles Moles can refer to:
* Moles de Xert, a mountain range in the Baix Maestrat comarca, Valencian Community, Spain
* The Moles (Australian band)
*The Moles, alter ego of Scottish band Simon Dupree and the Big Sound
People
*Abraham Moles, French engin ...
per litre (mol/L, often abbreviated to M for
molarity
Molar concentration (also called molarity, amount concentration or substance concentration) is a measure of the concentration of a chemical species, in particular of a solute in a solution, in terms of amount of substance per unit volume of solu ...
), moles per cubic decimetre (mol/dm
3), kilomoles per cubic metre (kmol/m
3) or in terms related to those used in particular titrations (such as
titre
Titer (American English) or titre (British English) is a way of expressing concentration. Titer testing employs serial dilution to obtain approximate quantitative information from an analytical procedure that inherently only evaluates as positiv ...
s). A simple standard is obtained by the dilution of a single element or a substance in a soluble solvent with which it reacts.
A primary standard is a reagent that is extremely pure, stable, has no waters of hydration, and has high molecular weight. Some primary standards of titration of acids include sodium carbonate.
Uses
A known volume of a solution of acid can be standardized by titrating it against a solution of alkali of known concentration. Standard solutions are also commonly used to determine the concentration of an
analyte species. By comparing the
absorbance
Absorbance is defined as "the logarithm of the ratio of incident to transmitted radiant power through a sample (excluding the effects on cell walls)". Alternatively, for samples which scatter light, absorbance may be defined as "the negative lo ...
of the sample solution at a specific wavelength to a series of standard solutions at differing known as concentrations of the analyse species, the concentration of the sample solution can be found via
Beer's Law. Any form of
spectroscopy can be used in this way so long as the analyte species has substantial absorbance in the spectra. The standard solution is a reference guide to discover the molarity of unknown species. Titration methods can be used to acquire the concentration of a standard solution. These involve using equipment such as a burette.
Properties
The properties of a standard solution for titrations are:
# Its concentration must remain constant all the time. This is so that there is no need for restandardization.
# Its reaction with the analyte must be rapid in order to minimize the waiting period after addition of each reagent.
# Its reaction must be reasonably complete.
# It should be possible to describe the reaction by a balanced chemical reaction.
# A method must exist for detecting the equilibrium point.
References
*
Analytical chemistry
{{Chemistry-stub