why should samples be weighed rather than measured volumetrically when determining the percent acetic acid in vineger
Mass does not change with temperature but volume does.
Samples should be weighed rather than measured volumetrically when determining the percent acetic acid in vinegar because acetic acid is a liquid and its concentration can be affected by factors such as temperature, pressure, and evaporation. Weighing the samples is a more accurate and reliable method for determining the concentration.
To determine the percent acetic acid in vinegar, you can follow these steps:
1. Weigh a sample of vinegar: Start by weighing a specific amount of vinegar using an analytical balance. The exact amount will depend on the desired precision and the equipment you have available.
2. Dilute the vinegar: If the vinegar is concentrated, it may need to be diluted with distilled water to ensure accurate measurements. This step is necessary because concentrated vinegar can have higher percentages of acetic acid, which can affect the precision of the analysis.
3. Titrate the sample: Prepare a standardized sodium hydroxide (NaOH) solution of known concentration. The sodium hydroxide will react with the acetic acid in the vinegar through a process called titration. The reaction between acetic acid and sodium hydroxide is as follows:
CH3COOH + NaOH → CH3COONa + H2O
The sodium hydroxide is added to the vinegar until the reaction is complete. This is typically indicated by a color change when using a suitable indicator, such as phenolphthalein. The volume of sodium hydroxide solution required to reach the end point of the reaction is recorded.
4. Calculate the percent acetic acid: By knowing the volume of the standardized sodium hydroxide solution required to neutralize the acetic acid, you can calculate the amount of acetic acid present in the vinegar sample. This information, combined with the weight of the sample, allows you to determine the percent acetic acid.
Overall, weighing the sample and performing a titration provides a more accurate way to determine the percent acetic acid in vinegar compared to a volumetric measurement alone.