if we tritrate weak acid(oxalic acid)with strong base(naoh).which indicator is used and why
Your School SUBJECT is CHEMISTRY.
The titration of a weak acid and strong base gives a pH at the equivalence point of between 8 and 10. The k1 for oxalic acid is fairly strong but hard to separate from k2. So you want an indicator that will change about 8-10. Phenolphthalein is suitable for that.
To determine the endpoint of a titration between a weak acid (such as oxalic acid, H2C2O4) and a strong base (such as sodium hydroxide, NaOH), we typically use a pH indicator that changes color in the vicinity of the pH at the equivalence point.
An appropriate indicator for this titration is phenolphthalein. Phenolphthalein is a weak acid itself and exists in an acidic form (HIn) and a basic form (In-). In an acidic solution, it is colorless, but as the pH increases and becomes more basic, it changes to a pink color.
The choice of phenolphthalein as the indicator is based on the pH range where the titration occurs. When a strong base is added to a weak acid, a buffering effect occurs, resulting in the solution's pH increasing gradually. At the equivalence point of this specific titration, the moles of acid will be exactly neutralized by the moles of base. At this point, the solution becomes slightly basic, causing phenolphthalein to undergo a color change from colorless to pink, indicating the endpoint of titration.
It's important to note that the choice of indicator depends on the specific acid and base being used in the titration. Phenolphthalein is commonly used for strong acid-strong base titrations and weak acid-strong base titrations, but different indicators may be employed for other titrations.