How to Make Standard Solutions and What Are Their Uses? One of the most critical tasks in chemistry, especially in analytical chemistry, is determining the concentration of substances in an unknown solution. Standard solutions are tools that chemists use to quickly and accurately determine the concentration of unknown substances. The concentration of standard solutions is usually expressed in moles per liter (mol/L or molarity) and moles per cubic decimeter (mol/dm3).
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What Are Primary Standards & Standard Solutions? Standard solutions are prepared by dissolving the primary standard in a solvent. The prepared standard solution has a known, accurate concentration. This solution is then used in the laboratory to determine the concentration of a solution of interest. The primary standard has specific properties: 1- It is solid. Substances used as the primary standard are usually inexpensive and readily available. 2- It is very pure. The substance is prepared in analytical grade, with a purity of 99.9%. 3- It has a consistent formula, and its hydration degree remains constant.
4- It does not react with substances in its environment and atmosphere. The substances used as primary standards do not absorb moisture or carbon dioxide from the air and are not oxidized in the air. 5- It has a relatively high molar mass. This helps minimize errors in weighing. 6- It is soluble in the solvent used to prepare the secondary standard solution. One of the main differences between primary and standard solutions is that the primary standard has high purity (99.9%) but lower reactivity. In contrast, standard solutions have lower purity and higher reactivity. Primary standards are rarely contaminated because of their low reactivity, while secondary standard solutions are highly reactive and can be easily contaminated. Therefore, before using secondary solutions, you should standardize them.
Preparation of Standard Solutions To prepare a standard solution, a certain amount of the primary standard is carefully weighed on a scale and then transferred to a volumetric flask. The solvent is added, and after dissolving the primary standard substance, the volume is increased. Basically, a standard solution is obtained by diluting a primary element or substance in the solvent. In standard solutions, the ratio between the amount of solute and solution or the amount of solute and solvent is known. By knowing the amount of solute and the amount of solvent in the solution, the concentration of the standard solution can be determined. Note that different methods are used to express the concentration. As an example, let’s see how a standard solution of sodium carbonate is prepared. Anhydrous sodium carbonate is used as the primary standard for this purpose; briefly: 1- Place some distilled water into a volumetric flask. 2- Add 1.300 grams of anhydrous sodium carbonate. 3- Bring the total volume up to 250 mL by adding distilled water. Now, you can calculate the concentration of this standard solution using the following formula: C= (m/M)/V Where C is the concentration of the standard solution (in mol/L), m is the amount of the primary standard used as solute (in grams), M is the molar mass of the primary standard, and V is the volume of the solution (in liters). The molar mass of anhydrous sodium carbonate (Na2CO3) is 105.9888 g/mol. Thus, you can calculate the concentration of the prepared standard solution as 0.04906 mol/L.
Application of Standard Solutions Standard solutions are usually used to determine the concentration of other substances. For example, standard titration solutions are widely used to determine the concentration of an unknown substance. In addition, standard solutions are used to determine concentrations in spectroscopic analysis. For spectroscopic analysis, first, standard solutions of different concentrations are prepared. A standard curve is plotted using these solutions. Using the plotted curve, the concentration of the unknown substance can be easily determined based on the intensity of its absorption in spectroscopy.
Standard Solutions from Loba Chemie Loba Chemie offers high-quality standard solutions for atomic absorption spectroscopy (AAS) measurements. AAS is the most sensitive technique for determining and measuring metal impurities. Loba Chemie’s standard solutions are prepared by dissolving a primary standard with a purity of 99.9% in the solvent acid. Usually, hydrochloric or nitric acids are used as the solvent. These standard solutions meet strict criteria, including the National Institute of Standards and Technology (NIST) standard.