QUANTITATIVE ANALYSIS OF SODA ASH BY DOUBLE-INDICATOR TITRATION

Z.C. HACHERO DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING, COLLEGE OF ENGINEERING

UNIVERSITY OF THE PHILIPPINES, DILIMAN QUEZON CITY, PHILIPPINES DATE PERFORMED: SEPTEMBER 19, 2015INSTRUCTOR’S NAME: SEARLE AICHELLE DUAY

1. Discuss the use of a more dilute NaOH solution for the standardization of NaOH.

A stronger concentration would make it impossible to titrate accurately and actually see the neutralization take place. With a largely known dilution, you can calculate the same reaction but the 'color indicator' will allow you to slowly achieve the perfect amount in mL for a pale solution and not overtitrate, which will in the end make your calculations off. That and NaOH is VERY VERY bad to use concentrated.

2. Discuss the rationale behind the dilution and aliquoting of the aspirin sample.

Diluting and using only the aliquot of the aspirin sample allows an easier titration setup. Only a small amount of the titrant was needed to reach the endpoint.

3. Discuss the principle behind the use of back titration in the analysis of aspirin tablet.

Aspirin is an ester which is very easily hydrolyzed. So easily that during a normal titration with NaOH, the alkaline conditions break it down leading to errors in analysis. In addition its water solubility is low. To overcome these problems, Aspirin is completely hydrolyzed to salicylic acid and acetic acid with hot, excess NaOH. The NaOH in excess is then titrated with standardized

acid (HCL or H2SO4) to calculate the amount used in the reaction with Aspirin and thereby the amount of drug in the flask.

4. Discuss the importance of simmering the tablet in NaOH solution for 20 minutes.

The simmering process is a crucial part of this experiment to ensure that the aspirin sample which is a monoprotic acid will completely dissociate into acetic acid and salicylic acid during the hydrolysis.

5. Discuss the possible sources of errors and their effect on calculated parameters.

Possible sources of error in the experiment include the faulty titration and standardization of solutions, faulty weighing of samples that can lead to over titration and wrong computations, and incomplete hydrolysis of sample.

REFERENCES:[1] Skoog, D., West, D., Holler, F.J., Crouch, S.,

Chen, S. Introduction to Analytical Chemistry 8th ed. Cengage Learning, Singapore. 2012.

[2] Harris, D. Quantitative Chemical Analysis 8 th

ed. W.H. Freeman and Company, New York. 2010.

[3] Determination of the Carbonate Content of a Soda Ash Sample.

http://www.csudh.edu/oliver/che230/labmanual/carbnate.htm. (Accessed September 24, 2015)