Quantitative Analysis of Soda Ash by Double-Indicator Titration Keywords: Soda ash, double-indicator, neutralization
RESULTS AND DISCUSSION
Titration is a method of chemical analysis that can be used to determine the amount of analyte present in the solution through the determination of the endpoint of the reaction (Dartmouth College, 2000). In the experiment, the percent composition of soda ash was determined. Soda ash could be composed of NaOH, Na2CO3, NaHCO3, or a mixture of NaOH and Na2CO3, and NaHCO3 and Na2CO3. A mixture of NaOH and NaHCO3 is impossible because OH- and HCO3- will react to form CO3- and H2O. This reaction could cause errors in the analysis because it could change the concentration of the HCl standard. To be able to determine the composition, acid-base titration, which uses the concept of a neutralization reaction, was used. Also, double-indicator titration was used since soda ash could contain two bases. This means that there could be two endpoints in the titration process. Phenolphthalein and methyl orange indicators were used. Bromocresol green indicator could also be used in place of methyl orange indicator as it is also an acid-range indicator and actually encompasses a better and more suitable pH range for the experiment. The primary standard that was used to standardize HCl (titrant) was Na2CO3 which has 99% purity. CO32- + H3O- HCO3- + H2O 
HCO3- + H3O+ H2CO3 + H2O CO2 + 2H2O 
According to the University of Adelaide, primary standards must be extremely pure, stable, has no waters of hydration, and has a high molecular weight. These characteristics qualify Na2CO3 to be a valid primary standard for HCl. However, NaOH cannot be used as a primary standard for HCl. Obviously, NaOH has a relatively low molecular weight. Moreover, it easily absorbs water from the air, and it cannot be weighed and diluted so getting its exact concentration would be not so accurate (Spurlock, 2012). Soda ash was weighed and diluted...
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