why we use phenolphthalein indicator in the determination of the strenght of NAOH by using standard oxalic acid why not the others indicator?
What others specifically. The general answer is that phenolphthalein changes color more nearly at the equivalence point for your titration than the other indicators you might have available.
In this titration the end point will occur at a pH hihger then 7 since it involves a strong base and weak acid.(therefore the salt CH3COONA will be basic in nature).The point is 8,5-9.00 and therefore the most suitable indicator will be phenolphtalein since the end points range is contained along the pH in which the indicator(phenolphtalein) is active.
Phenolphthalein indicator is commonly used in the determination of the strength of sodium hydroxide (NaOH) with standard oxalic acid because it undergoes a clear color change at a pH range between 8.2 and 10. The color transition occurs when NaOH reacts with oxalic acid to form sodium oxalate, which is neutral. Here's why phenolphthalein is preferred over other indicators:
1. pH range: Phenolphthalein has a pH range that matches the equivalence point of the NaOH-oxalic acid reaction. Other indicators may not exhibit a sharp color change within this pH range, leading to less accurate results.
2. Sensitivity: Phenolphthalein is highly sensitive to changes in pH. It starts as colorless in an acidic solution and turns pink as the pH becomes more basic. This sensitivity ensures that a small volume of oxalic acid can be used to neutralize a given volume of NaOH.
3. Clear endpoint: Phenolphthalein provides a distinct endpoint, where the color change is easily observed. The appearance of pink color indicates the completion of the reaction and helps in determining the amount of NaOH present in the solution.
It's important to note that different indicators may be used for other titrations depending on the reaction being studied and the desired pH range for color change. Phenolphthalein is specifically chosen for NaOH-oxalic acid titrations due to its appropriate pH range and clear color change.
Phenolphthalein is commonly used as an indicator in the determination of the strength of sodium hydroxide (NaOH) using standard oxalic acid. The choice of indicator depends on several factors, such as the pH range over which the indicator undergoes a color change.
Phenolphthalein is particularly useful in acid-base titrations because it changes color within a suitable pH range for this specific titration. In the case of NaOH and oxalic acid, the reaction is a strong base (NaOH) reacting with a strong acid (oxalic acid).
To determine the strength of NaOH, we titrate a known volume of NaOH solution with a standard solution of oxalic acid that has a known concentration. The reaction between NaOH and oxalic acid is:
2 NaOH + H2C2O4 → Na2C2O4 + 2 H2O
During the titration, the phenolphthalein indicator is added to the NaOH solution. Phenolphthalein is colorless in acidic solutions and turns pink when the pH of the solution becomes slightly basic, around pH 8.2 to 10.0.
At the beginning of the titration, the oxalic acid is slowly added to the NaOH solution while continuously stirring. The pink color will initially disappear due to the acidic nature of the oxalic acid.
As the titration proceeds, the oxalic acid solution becomes gradually neutralized by the NaOH until the equivalence point is reached. The equivalence point is when the number of moles of oxalic acid is equal to the number of moles of NaOH in the solution.
At the equivalence point, all the NaOH has reacted with the oxalic acid, and the solution becomes slightly basic due to the presence of excess NaOH. This basic environment causes the phenolphthalein to turn pink, indicating that the reaction is complete.
Other indicators may also be suitable for this titration, but phenolphthalein is commonly preferred due to its distinct color change within the required pH range. However, if you have another indicator in mind, it is worth checking its pH range to determine if it is appropriate for this specific reaction.