why NaOH must be standardized?
It is not possible to purchase NaOH that is 100% NaOH. Although pure NaOH can be manufactured, it picks up CO2 and H2O from the atmosphere immediately so the stability as pure 100% is fleeting. Therefore, we must standardize it to know the concentration of the solution we prepare.
NaOH, which stands for sodium hydroxide, is a strong base commonly used in various chemical processes and applications. It is also frequently used in laboratory work, particularly in titrations and analytical chemistry. The process of standardization involves determining the exact concentration or molarity of a given solution, in this case NaOH.
Here's why NaOH needs to be standardized:
1. Variation in purity: Commercially available NaOH may not be of uniform purity, meaning it can contain impurities or water, which can affect its concentration. Standardization helps determine the actual concentration of NaOH, accounting for any impurities present.
2. Hygroscopic nature: NaOH is highly hygroscopic, which means it easily absorbs moisture from the surrounding air, leading to changes in its concentration. Standardizing NaOH involves weighing the solution accurately to account for any water absorbed, ensuring precise measurements.
3. Accurate titration: NaOH is commonly used as a titrant in acid-base titrations. In order to accurately determine the unknown concentration of an acid (or any other substance in an acid-base reaction), it is essential to have a precise and known concentration of NaOH. This is achieved through standardization.
Now, let's discuss how the standardization of NaOH is carried out:
The standardization process involves titrating a known quantity of a primary standard acid against a freshly prepared NaOH solution. A primary standard is a highly pure compound with a known molar mass that can be used to determine the concentration of other substances.
The steps for standardizing NaOH are as follows:
1. Weigh a known amount of a primary standard acid, such as potassium hydrogen phthalate (KHP), and dissolve it in distilled water to create a solution.
2. Pipette a measured volume of the prepared primary standard acid solution into a flask or beaker.
3. Add a suitable indicator, such as phenolphthalein, to the acid solution. It changes color when the acid is completely neutralized.
4. Titrate the acid solution by adding NaOH solution from a burette until the indicator changes color permanently. This indicates that the acid has been completely neutralized.
5. Record the volume of NaOH required for titration. This volume, along with the molar mass of the primary standard acid, allows the calculation of the concentration of the NaOH solution.
By standardizing NaOH, you can eliminate potential errors due to impurities or fluctuations in concentration, ensuring accurate and reliable results in various laboratory applications.