Analysis of Soda Ash and Volumetric Analysis of a Carbonate-Bicarbonate Mixture

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Analysis of Soda Ash and Volumetric Analysis of a
Carbonate-Bicarbonate Mixture
Manalo, Ma. Cristina Joyce B.
Department of Chemical Engineering, Faculty of Engineering
University of Santo Tomas
Espana, Manila

A. Abstract

Crude sodium bicarbonate or commonly known as soda ash may contain amounts of impurities like chlorides and hydroxides. The total acid neutralizing capacity of a soda ash sample, its alkalinity value, was stated in terms of mass of sodium carbonate. In doing so, any sodium hydrogen carbonate present in the sample was converted to its equivalent neutralizing capacity in terms of sodium carbonate. A mass of the impure sample was dissolved and diluted in distilled water. 3 drops of indicator was mixed and the solution was titrated with the standard acid (HCl) to the endpoint. Volumetric analysis is a quantitative analytical technique which employs a titration in comparing an unknown with a standard. A titration reaction may use two indicators, as in the analysis of carbonate-bicarbonate mixture. The two methods involved in this experiment were the classical method and the potentiometric method. In classical method, the endpoints of the two indicators (phenolphthalein and methyl orange) were determined using titration method. In the potentiometric method, the progress of the titration was monitored using a pH meter. B. Introduction

Sodium carbonate is an important industrial chemical. It is used in the manufacture of soap, glass, paper and as a source of alkalinity, that is, as a base. Glass, paper and as a source of alkalinity, that is, as a base. Soda ash, which is primarily sodium carbonate, contains unreacted sodium hydrogen carbonate and other impurities. The total acid neutralizing capacity of a soda ash sample, its alkalinity value, can be stated in terms of percent sodium carbonate. In doing so, any sodium hydrogen carbonate present in the sample is converted to its equivalent neutralizing capacity in terms of sodium carbonate. That is, a 100% NaHCO3 sample is represented as a 50% Na2CO3 sample in terms of its acid neutralization capacity. The goal of this experiment was to determine the mass of sodium carbonate in the soda ash sample to compute for the %alkalinity. Volumetric analysis is a quantitative analytical technique which employs a titration in comparing an unknown with a standard. Numerous inorganic species can be determined by titration with strong acids or bases. The analysis of mixtures containing hydroxide, carbonate and bicarbonate ions requires double titration, one with a base-range indicator, such as phenolphthalein and the other with an acid-range indicator, such as methyl orange. The goal of this experiment was to calculate for the percent carbonate and bicarbonate in the sample by taking the volume of standard acid (HCl) needed to reach the two endpoints. C. Review of Related Literature

D. Methodology
I. Analysis of Soda Ash

a. Preparation of 0.10 M HCl
500 mL of distilled water was measured and put to a beaker. 4.2 mL of concentrated HCl was added carefully and slowly to the beaker. The solution was stirred and then transferred into a labelled storage bottle. b. Standardization of 0.10 M NaOH

Two burets were prepared and with one buret, 20 mL of the standard NaOH was transferred into a dry container. 3 drops of methyl orange were added. The acid buret was filled with the acid to be standardized and the acid was titrated with the base until the formation of an orange-colored solution. c. Determination of Total Alkalinity of the Soda Ash

A mass of the unknown soda ash sample ranging from 0.3000 to 0.6000 grams was weighed and dissolved in 150 mL of distilled water. The solution was transferred to a 250-mL volumetric flask and was diluted with distilled water to the etch mark. The flask was inverted several times thoroughly mixing the solution. 50 mL aliquot from the solution was measured accurately. 3 drops of methyl orange...
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