Department of Chemical Engineering, Faculty of Engineering
University of Santo Tomas
Titration is a laboratory method in which the endpoint of a reaction is determined quantitatively. In this experiment, the amount of soda ash present in a sample was determined and the alkalinity reported as it was titrated using HCl as the titrant. Also, the percentage amount of Na2CO3 and NaHCO3 present in the sample was determined at the end of the experiment.
Soda Ash (Na2CO3) or sodium carbonate is commonly used as a cleaning agent and known as “washing soda”. It was found to be alkali and has a high pH in concentrated solutions. It is soluble in water but its solubility decreases slightly as the temperature increases above 35.4○C or 95.7○F. It is used in many different fields such as manufacturing, at home or in industries. It can be produced either synthetically or naturally. Trona, a mineral that can be found in evaporated lake beds, is a common natural source of production. It can also be found in some salt waters. It is also a safe substance that can be handled without extraordinary precautions but when extracting this in laboratories, a prolonged exposure to this powder could be harmful. When it comes in contact with the eyes, it can irritate it and when it is ingested, it corrodes the stomach lining.
The experiment is required for titration using an HCl solution. First the titrant, HCl, was prepared in which a 4.2 mL concentrated HCl was added to a 500.0 mL of distilled water. It was stirred and transferred to an Arrhenius storage bottle. After preparing, it was then standardized in which the prepared solution was used as a titrant and a standard NaOH as the analyte. An indicator methyl orange was added by adding 3 drops to the analyte then it was titrated until the orange-colored solution appeared. The molarity was computed after the titration. An unknown soda ash sample weighing an approximately 0.3000g to 0.6000g was dissolve in a 150.0 mL distilled water and was transferred in a 250.0 mL volumetric flask as the solution was diluted to the mark by distilled water. An aliquot of 50.0 mL was used as the testing analyte in which 3 drops of methyl orange indicator was added. It was titrated with the prepared titrant until the end point was reached. The alkalinity of the sample was then computed. Another experiment, the volumetric analysis of carbonate-bicarbonate mixture, was also performed using titration. There were two set-ups needed in order to perform this. The first set-up used the pH meter. A 2.0000g of the unknown solid sample was weighed and dissolved in a 100 mL distilled water. It was transferred in a 250 mL volumetric flask and an aliquot of 50.0 mL was used as the analyte. 3 drops of the phenolphthalein indicator was added to the analyte and was titrated with HCl until the light-pink end point solution appeared. The volume was recorded as the phenolphthalein end point. Also, 3 drops of methyl orange indicator was added in the solution and once again was titrated to obtain the orange color end point of the indicator. The volume was recorded as the methyl orange end point. Same set-up was used on the other but the pH was observed every 0.25 mL until it reached the two end points. The results was plotted on a graph in excel to show the titration curve.
Results and Discussion
In standardization of NaOH, it was found that the average molarity of HCl was 1.047 M, as reflected in Table 1. Standardization of NaOH|
| Trial 1| Trial 2|
Vol of NaOH| 20.0 mL| 20.0 mL|
Vf HCl| 21.9 mL| 42.1mL|
Vi HCl| 0.0 mL| 21.9mL|
Vol of HCl used| 21.9 mL| 20.2mL|
M NaOH| 0.0955 M| 0.0955 M|
M HCl| 1.047 M| 1.047 M|
Ave M HCl| 1.047M|
Table 1. Standardization of NaOH
A sample was dissolved and tested using titration...