added and is titrated again with HCl until thecolor of the solution turns pale yellow. The solution is then boiled to remove CO2, cooled and then titrated again with HCl untilit reaches endpoint.For this part, three trials were again conducted. The volume of HCl required to reach the phenolphthalein endpoint was compared to the volume required to reach the methyl orange endpoint. If the two volumes are equal, then the sample contains only Na2CO3. If the second volume is equal to zero, then the sample contains only NaOH. If the first volume is zero, then the sample contains only NaHCO3. If the first volume is greater than the second, then the sample contains a mixture of NaOH and Na2CO3. Lastly, if the first volume is less than the second, then the sample contains a mixture of NaHCO3and Na2CO3(Table 2). A third mixture that can be formed from the three compounds present is NaOH and NaHCO3. This mixture however, will not exist because the two compounds will react to form Na2CO3and either NaOH or NaHCO3-whichever is in excess.
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Table 2. Comparison of HCl vol. atphenolphthalein endpoint and methyl orange endpoint.V1vs V2ComponentV2= 0NaOHV1= V2Na2CO3V1= 0NaHCO3V1> V2NaOH and Na2CO3V1< V2NaHCO3andNa2CO3It was observed in two out of three trials that the volume of HCl required to reach the phenolphthalein endpoint is less than the volume required to reach the methylorange endpoint. From this observation, it is concluded that the soda ash sample analyzedcontained both Na2CO3and NaHCO3. (Table3)Table 3. Sample AnalysisTrial123Sample Weight, g0.101±0.0010.111±0.0010.100±0.001Net vol. HCl atphenolphthaleinendpoint, ml4.1 ±0.143.1 ±0.144.8 ±0.14Net vol. HCl atmethyl orangeendpoint, ml7.8 ±0.146.2 ±0.144.3 ±0.14V1vs V2<<>From these data the percent composition of soda ash was calculated withan average of 9.85% for NaHCO3and 20.35% for Na2CO3. The calculated values were inconsistent for the three trials. This was because for every trial, a different person was doing the titration. (Table 4)Table 4. %Composition of Soda Ash%Composition of SodaAshTrial1Trial2Trial3AverageNaHCO315.23±0.38811.43±0.3882.09±0.3889.58 ±0.672Na2CO321.3±0.06814.42±0.06825.34±0.06820.35±0.119
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