Identification of Unknown Organic Acid

Identification of an Unknown Organic Acid

November 15,2007

John A. Doe

Partner: Julie Jones TA: Michael Smith Lab Sec # 22, Tuesdays 9-12

Abstract The purpose of this experiment is to determine the molar mass and identity of an unknown acid (#79) by means of titration. Analysis of the data obtained from the titration reveals that the unknown acid has a molar mass of 1.40 x lo2glmol with a percent error of 1.45%. This value is most closely associated with salicylic acid (molecular mass of 138.1 glmol). Therefore it has been determined (within reasonable error limits) that acid #79 is salicylic acid. Theory The purpose of this experiment was to determine the molar mass of an unknown acid via titration. In a titration a solution with a known concentration, or standard solution, is used to neutralize an amount of solution with an unknown concentration. By adding an acid-base indicator (phenolphthalein) to the solution, one can observe a color change which marks the point at which the neutralization reaction comes to completion, called the equivalence point. Finally, by measuring the volume of standard solution required to completely neutralize the acid, the molecular mass of the acid can be calculated using stoichiometry. In this case the acid was assumed to be monoprotic which means that for every mole of base that reacted one mole of acid reacted also. In other words, the stoichiometric ratio between the acid and base was assumed to be one-to-one. This particular experiment used a solution of known concentration of sodium hydroxide as the standard solution; so by measuring the volume of sodium hydroxide required to neutralize the acid and combining the knowledge that the acid is monoprotic, the molar mass of the acid (# 79) could be determined.

Procedure

.V

All procedural information is tabulated in the CH 224H Laboratory Manual, pp. 20-21

1

Data

For each trial, the following mass measurements of the acid were taken prior to titration...