In a laboratory, primary standard solutions are highly pure and stable solutions that are used to accurately determine the concentration of other substances through a process called titration. Primary standard solutions are typically used when high precision and accuracy are required. Some common examples of primary standard solutions include:
Sodium hydroxide (NaOH) solution: Used as a primary standard for acid-base titrations. Its concentration can be precisely determined by weighing and dissolving a known amount of pure sodium hydroxide in water.
Potassium hydrogenphthalate (KHP) solution: It is often used as a primary standard for acid-base titrations. KHP is a solid compound that can be dissolved in water to prepare a solution of known concentration.
Sodium carbonate (Na2CO3) solution: Sodium carbonate can be used as a primary standard for standardizing acids. It is prepared by accurately weighing pure anhydrous sodium carbonate and dissolving it in water.
Potassium permanganate (KMnO4) solution: KMnO4 is a primary standard for titrations involving reducing agents. Its concentration can be determined by preparing a solution of known strength and titrating it against a reducing agent.
Ferrous ammonium sulfate (FAS) solution: FAS is commonly used as a primary standard for titrations involving oxidizing agents, such as potassium permanganate. Its concentration can be accurately determined by preparing a solution of known strength and titrating it against a standard solution of the oxidizing agent.
These are just a few examples of primary standard solutions used in laboratories. The specific choice of a primary standard depends on the nature of the analysis and the substances being tested. It's important to handle and store primary standard solutions carefully to maintain their purity and accuracy.