What is a primary standard in analytical chemistry?

A primary standard in analytical chemistry refers to a highly pure chemical that is used to determine the concentration of solutions. This characteristic is crucial because the accuracy of quantitative analysis relies on the purity of the standard being used. When using a primary standard, it is essential that the substance has a known and stable composition. This allows for precise calculations during titrations or other analytical procedures, as the reactions can be directly correlated with the amounts of the primary standard.

The correct use of primary standards involves dissolving a known mass of the standard in a specific volume of solvent to create a solution of known concentration. This solution can then be used to calibrate other solutions or for quantitative analysis, making it a fundamental concept in analytical chemistry.

Other provided options describe related concepts but do not meet the definition of a primary standard. A solution with a known concentration is derived from a primary standard but does not itself represent a primary standard. A reagent that reacts with all other substances can refer to various chemicals but is not specific to the characteristics of a primary standard. Similarly, referring to a temperature-dependent reaction standard does not align with the definition of primary standards, which focus on purity and stability rather than temperature effects.