Sodium benzoate is a common preservative used in food, medications, and cosmetics.
Its estimation is important to ensure product safety and compliance with regulations.
The quantitative determination of sodium benzoate can be conducted using various methods, including UV spectroscopy, high-performance liquid chromatography (HPLC), and titration.
Here's an overview of a typical titration method for estimating sodium benzoate in a sample:
Materials:
Sodium benzoate sample
Distilled water
0.1M Hydrochloric acid (HCl)
0.1M Sodium hydroxide (NaOH)
Phenolphthalein indicator
Procedure:
1. Preparation of Sample:
Dissolve a known weight of the sample containing sodium benzoate in distilled water.
Make sure the solution volume is known for concentration calculations.
2. Acidification:
Add a few drops of phenolphthalein indicator to the sodium benzoate solution.
Titrate with 0.1M HCl until the pink color disappears.
This step ensures that all the benzoate is converted to its acidic form (benzoic acid).
3. Back Titration:
After acidification, add a known excess amount of 0.1M NaOH to the mixture.
The solution will turn pink again.
Now, titrate this solution with 0.1M HCl until the pink color just disappears. Record the volume of HCl used.
4. Calculation:
The amount of NaOH that reacted with the sodium benzoate can be calculated by the total amount of NaOH added minus the amount of HCl used in the back titration.
From the moles of NaOH reacted, determine the moles of sodium benzoate (since they react in a 1:1 ratio).
Finally, calculate the concentration of sodium benzoate in the sample based on the initial volume of the sample solution.