Quantitative Analysis of Soda Ash by Double-Indicator Titration

1 January 2017

This experiment aims to analyze the percent composition of a substance mixture by using double indicator titration. The analyte used is the soda ash which is titrated with an HCl titrant, standardized by 1o Na2CO3. The indicators used are phenolphthalein for basicity and methyl orange for acidity. The two volumes of the titrant are then used to calculate percent composition of soda ash analyte. Statistical parameters such as relative standard deviation and confidence limits are also calculated.

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At the end of the experiment, the calculate percent /calculated average percent by mass of Na2CO3 is 27. 6% with a relative standard deviation of 64. 1 ppt and confidence intervals of 43. 5% – 11. 7% and the average percent by mass of NaHCO3 is 5. 23% with a relative standard deviation of 128 ppt and confidence intervals of 11. 3% – -0. 8%. With these results and the fulfilled objectives, the experiment was a success Introduction This experiment focuses in the analysis of soda ash, a widespread industrially used substance in petroleum refining, glass making, detergent anufacture, water treatment etc. It can be a pure compound of sodium carbonate, sodium bicarbonate or sodium hydroxide or the mixture of the three with compatible percent compositions.

These compositions are determined by acid-base titrations, a volumetric process in determining the concentration of a substance in a certain solution which uses a base or acid as the titrant. The reaction between sodium carbonate and hydrochloric acid occurs in 2 stages, with the formation of bicarbonate ion as the intermediate product. (1) (2) Equation 1 shows the production of the bicarbonate on in the first titration and equation 2 shows that the bicarbonate is consumed in the second titration. Graph 1. Endpoints of HCl with Na2CO3 and NaHCO3 Graph 1 shows that sodium carbonate has two endpoints, the phenolphthalein endpoint which indicates neutralization of the carbonate ion and the methyl orange endpoint which indicates neutralization of the bicarbonate ion. Some terms concerning titration are: analyte, titrant, standard, equivalence point, end point, indicators. Analytes are the unknown substances to be analyzed. Standards are the substances with known oncentrations and they provide a reference to determine unknown concentrations or to calibrate analytical instruments.

Primary standards, reagents that are extremely pure, stable, have no waters of 1 hydration, and have high molecular weights, are used to determine the accurate concentration of the standard solution. Titrant is the reagent inside the burette that would be dropped in the analyte. The volume of the titrant that is used to completely neutralize the base or acid component of the analyte will be used to calculate for the concentration of the unknown substance in the analyte.

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