Lab 14: Titration

Lab Setup (Photo)  

Analyte at the Equivalence Point (Photo)  

Summary of Procedure 

Setup: We filled a burette with sodium hydroxide, a strong base, and carefully controlled its flow into an Erlenmeyer flask that was being stirred by a magnetic stir bar. This flask contained a mixture of 20 mL of water, about 7.5 mL of vinegar ( a weak acid), and several drops of the indicator phenolphthalein. We watched the impact the flow of base had on the solution in the flask, watching for the tell-tale flash of pink; we were supposed to turn the liquid a soft pink color. 

In this lab we performed two trials. 

On our first trial we added a few drops too many, causing the liquid to turn a shade of hot pink. 

Our second trial yielded slightly better results; after following the same steps, we cautiously dripped in the base, watching to see how long the pink color lingered after each drop.  This time the color produced was not as bright as the first trial's, and we believed that it would lighten with time. Thus, we decided that the second trial could be called a success. 

Data Table 

Percent Ionization of Vinegar 

Work and Concentration

Why is it so low? 
The percent ionization of vinegar is low because vinegar is classified as a weak acid; its pH is only about 2.4, which is significantly weaker than the acids with pH measures of 0. Because it is a weak acid, vinegar molecules will not all ionize when placed in water; only some will break apart while some will remain intact. Thus, not all of its molecules react, which is why it is classified as a weak acid. The percent ionization is a measurement of the rate at which the particles of a certain acid or base ionize, with the numerator being the amount of ionized substance and the numerator being the original amount of that acid or base. Strong acids such as hydrochloric acid usually has a percent ionization of 100%, meaning that all of its molecules ionize when prompted.