Lab 14: Titration Lab

Looking happy with our titration setup even though the lab is very stressful

In this lab, my partners Meghana, Maya, Katie, and I titrated acetic acid with a strong base, sodium hydroxide, in order to determine the percent ionization of the acid in vinegar. We started off by cleaning and then filling a burette with 50 mL of NaOH (base) that had a molarity of 0.25M. We then filled a flask with 7.25mL vinegar, which is made up of a large amount of acetic acid, and added four drop of phenolphthalein. The phenolphthalein we added was an indicator that changed color from clear to pink when it turned from an acidic form to a basic form. As we added drops of base to the acid, we saw the color of the acid turn from clear to pink, and then back to clear as the acid/base solution was stirred. As the solution took longer to turn back to clear after drops of base were added, we knew it was nearing the equivalence point between H+ ions and OH- ions. We added fewer drops at a time until the solution became a light pink and there were a higher amount of OH- ions. This meant that pH increased over 7 and the solution became a base.

• Trial One:
• Molarity of Acid: ?
• Molarity of Base: 0.25 M
• Volume of Acid: 0.00725 L
• Volume of Base: 0.0250 L
• Calculations:
• M1V1=M2V2
• M(.00725) = .25(.025)
• M = 0.86
• Trial Two:
• Molarity of Acid: ?
• Molarity of Base: 0.25 M
• Volume of Acid: 0.00720 L
• Volume of Base: 0.0255 L
• Calculations:
• M1V1=M2V2
• M(.0072) = .25(.0255)
• M = 0.89

Average concentration of the vinegar (acetic acid): 0.875 M

[H3O+] = 10^-pH = 10^-2.4 = 0.0040 M

Percent ionization: 0.0040 M / 0.875 M * 100 = 0.46%

Why is this such a low number?

We know vinegar is a weak acid, which means that not all of the ions break apart/ionize,  meaning there are not many H+ and OH- ions in the solution. Therefore, the percent ionization is very low.