Titration-Acetic Acid in Vinegar
Intro: Some commercial vinegars, such as white vinegar, are obtained by diluting 100% acetic acid. The usual percentage of acetic acid in vinegar is between 4.0% and 5.5%. The quantity of acetic acid in a sample of vinegar may be found by titrating the sample against a standard basic solution. You will titrate with burets to determine what volume of 1.00M sodium hydroxide solution is needed to neutralize a measured quantity of vinegar. The molarity of vinegar can be calculated from volume and molarity of sodium hydroxide and volume of vinegar.
CH3COOH + NaOH à NaCH3COO + H2O
Purpose: Determine end point of titration, calculate molarity and % acetic acid in vinegar.
Safety: goggles, apron
Procedure:
1. Fill buret to zero mark with 1.00M NaOH solution. Use note card with black horizontal line to accurately measure bottom of the meniscus. Record as initial volume (vi) to nearest 0.01mL.
2. Measure 20.0mL vinegar and pour into 125mL Erlenmeyer flask. Add 2 drops phenolphthalein, an indicator. Place white paper below flask to aid in color detection.
3. Dispense NaOH solution, swirling constantly, until faint pink color persists. SLOW DOWN TO A DROPWISE RATE AS COLOR FADES MORE SLOWLY OR YOU WILL MISS THE ENDPOINT.
4. Record final volume as Vf. Rinse flask. Repeat titration.
Data Table: Include units. Measure each volume to nearest 0.01 mL.
Trial / Concentration (M) NaOH / Vi NaOH / Vf NaOH / Volume (Vf-Vi) NaOH / Volume Vinegar1
2
Analysis: Show work, include units and substance. Circle answers. MacidVacid=MbaseVbase
1. Determine molarity of vinegar in each trial. Convert mLàL.
Trial1:______Trial2: ______
2. Calculate the average molarity of the vinegar (add 2 answers above and divide by 2).
______
3. Use Molarity from #2 to determine mass CH3COOH in 1.00L. (M=mol/L, then molesàgrams).
______
4. Convert 1.00L of vinegar to grams using density. Dvinegar=1000.g/1L
______
5. Calculate percentage of acetic acid in vinegar sample.
mass of acetic acid x100%;______
mass of vinegar ______