What are the factors that can cause titration of 25 mL mixture of sodium bicarbonate and sodium carbonate with HCL not to reach the end point especially after addition of two 25 mL aliquots of NAOH and 10ml BACO3? And why is it that 25ml aliquots of NAOH is used rather than 50 ml aliquot?

The factors that can cause titration of a mixture of sodium bicarbonate and sodium carbonate with HCl not to reach the end point can include:

1. Insufficient mixing: If the reaction mixture is not adequately mixed, it can affect the rate at which the reaction occurs, leading to a slow or delayed endpoint.

2. Presence of impurities: Impurities in the sodium bicarbonate and sodium carbonate mixture can interfere with the reaction and affect the endpoint. These impurities can react with HCl, consuming it before it reaches the target compounds.

3. Incorrect pH indicator: The choice of pH indicator can impact the detection of the endpoint in a titration. An inappropriate or weak indicator may not exhibit a clear color change at the equivalence point, making it difficult to determine the endpoint accurately.

4. Titration errors: Human errors during the titration process, such as inaccurate measurements or miscalculations, can also lead to a failure in reaching the endpoint.

Regarding the use of 25 mL aliquots of NaOH rather than 50 mL aliquots, there could be a few reasons:

1. Reaction rate: A larger volume of NaOH may react too quickly with the mixture, making it difficult to accurately observe the endpoint. Using smaller aliquots allows for finer control of the reaction rate, making it easier to detect the endpoint.

2. Precision: Using smaller aliquots allows for more precise measurements of volume, concentration, and stoichiometry, leading to more accurate results.

It's important to note that the choice of aliquot size can depend on the specific reaction conditions, concentration of the reagents, and desired precision in the titration process.