Standard solution

A solution of known concentration used in chemical analysis

A standard solution is a solution containing a precisely known concentration of an element or a substance. It is used in quantitative analysis to determine the concentration of other substances. Standard solutions are typically used in titrations, where they react with a solution of unknown concentration to determine its concentration.

Preparation

The preparation of a standard solution involves dissolving a known mass of solute in a solvent to achieve a desired concentration. The solute is typically a pure substance, and the solvent is usually distilled water. The concentration of the solution is expressed in terms of molarity, which is the number of moles of solute per liter of solution.

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A standard solution being prepared in a laboratory

To prepare a standard solution, the following steps are generally followed:

1. Weighing the Solute: A precise mass of the solute is weighed using an analytical balance. 2. Dissolving the Solute: The solute is dissolved in a small volume of solvent. 3. Diluting to Volume: The solution is transferred to a volumetric flask, and more solvent is added until the total volume reaches the desired level. 4. Mixing: The solution is thoroughly mixed to ensure uniform concentration throughout.

Applications

Standard solutions are essential in various fields of chemistry and biochemistry. They are used in:

• Titrations: To determine the concentration of an unknown solution by reacting it with a standard solution.
• Calibration: To calibrate instruments such as spectrophotometers and chromatographs.
• Quality Control: In industrial processes to ensure the consistency and quality of products.

Types of Standard Solutions

Standard solutions can be classified based on their use and preparation:

• Primary Standard Solutions: These are prepared from primary standards, which are highly pure, stable, and have a known formula weight. Examples include sodium carbonate and potassium dichromate.
• Secondary Standard Solutions: These are solutions whose concentration is determined by titration against a primary standard solution. They are used when a primary standard is not available.

Series of Dilutions

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A series of dilutions prepared from a standard solution

A series of dilutions is often prepared from a standard solution to create a range of concentrations for analysis. This is particularly useful in spectrophotometry and other analytical techniques where a calibration curve is needed.

Related pages

• Titration
• Molarity
• Volumetric analysis
• Analytical chemistry