Testing for water hardness using EDTA as a titrant:
Suggest a reason why the buffer is good for only a week. The buffer contains disodiumEDTAdihydrate, MgSO47H20 and distilled water. NH4Cl and NH4OH is also added then diluted.
I know that after a week, the buffer will be bad and no longer be possible to achieve a sharp endpoint, but I don't understand the reason behind it.
The reason why the buffer used in testing for water hardness using EDTA as a titrant is only good for a week is due to a process known as hydrolysis. Hydrolysis refers to the reaction between water molecules and the buffer components, which can change the pH of the solution over time.
The buffer solution in this case contains disodium EDTA dihydrate, MgSO4 7H2O, and distilled water, along with NH4Cl and NH4OH (ammonium chloride and ammonium hydroxide), which are added and then diluted. The purpose of the buffer is to maintain a stable pH during the titration process.
However, over time, the NH4Cl and NH4OH in the buffer undergo hydrolysis. In the presence of water, ammonium chloride (NH4Cl) can react with water to produce ammonium hydroxide (NH4OH) and hydrogen chloride (HCl). On the other hand, ammonium hydroxide can react with water to produce ammonia (NH3) and water. These reactions can shift the pH of the buffer solution, making it less effective in maintaining a stable pH.
As the pH of the buffer solution changes, the accuracy and precision of the titration are compromised. This can make it difficult to achieve a sharp endpoint, which is the point at which the indicator used in the titration changes color, indicating the completion of the reaction between EDTA and the metal ions responsible for water hardness.
Therefore, to ensure accurate and reliable results, it is recommended to prepare a fresh buffer solution whenever performing the water hardness test using EDTA as a titrant. This will help maintain the stability of the pH and optimize the accuracy of the titration.