Quantitative Analysis of Soda Ash by Double Indicator Method

1942 WordsSep 7, 20128 Pages
Quantitative Analysis of Soda Ash by Double Indicator Method Results and Discussion The experiment focuses in the use of double indicator titration in quantitative analysis of soda ash sample. Titration refers to the process of measuring the volume of titrant required to reach the equivalnece point. This method of analysis, is based on the chemical reaction aA + bB → products (1) where a is the molecules of the unknown substances to be analyzed or the analyte. Analyte reacts with b molecules of B that is the titrant. The titrant is the standard solution which is added from a buret to react with the analyte until the amount of T added equals the amount of A, which is when equivalence point is reached. It is determined through a…show more content…
From these values along with the obtained masses of Na2CO3(s) and its purity, the more accurate concentration of HCl was obtained using the formula MHCl= 2(g Na2CO3)(% purity)(net VHCl)(MW Na2CO3) (5) The overall equation for the reaction between sodium carbonate solution and dilute hydrochloric acid is: Na2CO3 + 2 HCl → 2NaCl + CO2 + H2O (6) If you had the two solutions of the same concentration, you would have to use twice the volume of hydrochloric acid to reach the equivalence point - because of the 1 : 2 ratio in the equation. Table 3. Titration of soda ash sample Trial Weight (g) VHCl(L) P henol- phthalein Methyl Orange 1 0.0998 ± 0.0002 0.0040 ±0.00005 0.0100 ±0.00005 2 0.0998 ± 0.0002 0.0041 ±0.00005 0.0119 ±0.00005 3 0.1002 ± 0.0002 0.0030 ±0.00005 0.00980 ±0.00005 On the other hand, table 3 shows the data obtained in the titration of soda ash sample with HCl. In the first part of the titration, where HCl was added to the sample solution with phenolphtalein indicator, the color change that was observed was from pink to faint pink. It is because the pH of the solution was alkaline nad phrnophthalein which works on such pH would determine the end point of the titration. Referring to equations (2) and (3), it would be observed that addition of more HCl would produce an acidic solution and that the need for methyl orange indicator which works best in such pH is necessary. The color change observed after the addition of
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