why is using phenophthalin in determination of acetic acid in vinegar.
Phenolphthalein is commonly used in the determination of acetic acid in vinegar because it acts as an indicator that changes color depending on the pH of the solution. When phenolphthalein is added to a solution, it remains colorless in acidic conditions (pH less than 7) and turns pink or red in alkaline conditions (pH greater than 7).
To determine the concentration of acetic acid in vinegar, an acid-base titration is often performed. In this titration, a base solution (such as sodium hydroxide, NaOH) is slowly added to a known volume of vinegar until the solution reaches the equivalence point, where all of the acetic acid has reacted with the base.
Here's how the determination of acetic acid in vinegar with phenolphthalein works:
1. Measure a known volume of vinegar (typically around 10 mL) using a pipette.
2. Add a few drops of phenolphthalein to the vinegar solution. The solution will remain colorless at this stage since vinegar is acidic.
3. Fill a burette with a standardized solution of sodium hydroxide (or any other base) of known concentration.
4. Slowly add the sodium hydroxide solution from the burette into the vinegar solution, while continuously swirling the mixture. The base will react with the acetic acid in the vinegar.
5. As the sodium hydroxide solution is added, the pH of the solution increases. Once all the acetic acid has reacted with the sodium hydroxide, the solution becomes slightly alkaline, causing the phenolphthalein to turn pink or red.
6. The point at which the phenolphthalein changes color indicates that the equivalence point has been reached. At this stage, the moles of sodium hydroxide added equals the moles of acetic acid in the vinegar.
7. Record the volume of sodium hydroxide solution required to reach the equivalence point, which can be read from the burette.
8. Finally, using stoichiometry, you can calculate the concentration of acetic acid in the vinegar solution based on the volume and concentration of the sodium hydroxide solution used.
Overall, phenolphthalein is a suitable indicator for this titration because its color change occurs around the pH range of acetic acid (around pH 4-6), making it easy to detect the endpoint of the reaction.