An Experiment to Prove the Bronsted-Lowry Theory

Discussion This experiment was able to prove the Bronsted-Lowry theory. In acid-base reaction, there is a transfer of a proton from the acid to the base. This experiment also proved the concept of mole to mole ratio, in which a solution with a known mole can be used to find characteristics such as the concentration of a reaction in a reaction. Through the experiment, the concentration of NaOH, and mystery of the unknown acid # 25 was accomplished. In both parts A and B of the experiment, a weak acid-strong base reaction occurred. Results indicate that unknown acid # 25 is oxalic acid which is a weak acid. When oxalic acid dissolves in water , a few of its molecules will ionize in water, and a small amount of hydronium ions are produced. When NaOH is added, the hydronium ions will react with the strong base. Due to the fact that oxalic acid is a weak acid, the end point is acheived much quicker than an unknown strong acid. Overall, the experimental data can be agreed with literature. Furthermore, there were a few sources of error that occurred. Firstly, bubbles that form at the nasal of the burette was not cleared in every titration trial. This would affect the volume of NaOH used to titrate the solutions by approximately 0.01ml. Moreover, it is not certain that the right amount of indicator was used for the titration of the unknown acid in trial 2. It is stated that 2 drops of indicator should be used. It was uncertain whether 1 drop or 2 drops were used. Another drop was added. Using the wrong amount of indicator, such as too much can shift the end point which tampers the results dramatically.

Conclusion The objective of this lab was to use a solution with a known concentration to establish the concentration of NaOH, and the molar mass of unknown acid # 25. The purpose of this lab was in fact achieved. In this experiment, the concentration of NaOH in part A was obtained, and the unknown acid was solved for by titrating the unknown solution with a solution of known concentration. In part A, the concentration of oxalic acid was 0.10356mol/L. When titrating a solution with known concentration (oxalic acid) with NaOH, it was discovered that NaOH had an average concentration of 0.1038 mol/L. There were three titrations completed. ( Titration #1 - 0.1050 mol/L, #2 - 0.1024 mol/L, #3 - 0.1040 mol/l .) In part B, an unknown acid was titrated with NaOH which has a known concentration. It is concluded that unknown acid #25 is diprotic, and has an average molar mass of 127.6 g/mol. Three titrations where completed. ( Titration #1 - 130.8 g/mol, #2 - 123.9 g/mol, #3 - 127.6 g/mol). Referring to the chart of possible unknown acids in the Fall 2013 Chem. Lab Manual on page 29, the unknown acid is oxalic acid which has a molar mass of 126.07 g/mol. Therefore the molar mass obtained, 127.6 g/mol is an acceptable value. Furthermore, correct measurement tools were identified and information about how to titrate accurately was given. The reliability of experimental methods is up to par, and can lead other experimenters wishing to complete this lab to attain accurate results. Although for even more accurate results, titrations should be done with 5-10 trials.