Department of Chemical Engineering, Faculty of Engineering
University of Santo Tomas
February 27, 2013
The analyte used is the soda ash which is titrated with an HCl titrant, standardized by 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. At the end of the experiment, the calculated average percent by mass of Na2CO3 is 4.92% and the average percent by mass of NaHCO3 is 5.07%.
Soda ash is the common name for sodium carbonate, a chemical compound frequently used in manufacturing, industry, and even around the house. Glass production is one of the primary uses for sodium carbonate. Detergents and cleaning agents may also make use of it, and it can be used in cooking or as a food additive, as well. Sodium carbonate is known by the chemical formula Na2CO3, in reference to the elements that make up its base composition: Na, which is sodium; C, which is carbon; and O, which is oxygen. The Na2CO3 combination does not usually occur in isolation in nature, however, so it must be intentionally refined by scientists. (see figure below)
This experiment focuses in the analysis of soda ash, a widespread industrially used substance in petroleum refining, glass making, detergent manufacture, 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.
A. Preparation and Standardization of 0.10 M HCl Solution
In preparing the HCl solution, 500 mL of distilled water and 4.2 mL of concentrated HCl were mixed together in a beaker, and then placed into a labelled storage bottle. The titration of the 20 mL NaOH containing 3 drops of methyl orange, was then started using a buret, filled with HCl. The molarity was then computed after recording the amount of HCl used in turning the solution to orange-colored.
B. Determination of Total Alkalinity of the Soda Ash
A solution, made of .30g to .60g of an unknown soda ash sample dissolved in 150 mL distilled H2O, was transferred into a 250-mL volumentric flask to dilute to the mark with distilled H2O. After mixing the solution, a 50 mL aliquot was taken and 3 drops of the indicator were added to the aliquot. The acid was then titrated until to the methyl orange endpoint. Using the data gathered, thepercent alkalinity of the sample was identified.
C. Preparation and Standardization of 0.10 M HCl Solution and 0.10 M NaOH
The solutions that were prepared in the Lactic Acid and Soda Ash experiments were used. D. Analysis of the Carbonate-Bicarbonate Mixture
First, the pH meter was calibrated by using specified buffers and rinsing the electrode with distilled H2O. The standard HCl was then transferred into a buret and was used as a titrant. Three drops of phenolphthalein indicator and 50 mL aliquot solution, with a composition of 2.00g solid sample and 100mL distilled H2O, were put into a beaker. In the acid, the electrode was immersed and the titration of the acid started. When the solution became pink-colored, the volume consumed was recorded. Next, with the same solution in the beaker, 3 drops of methyl orange were added. Same procedure of titrating was done until the solution became orange-colored. The volume used, again, was recorded.
Results and Discussion
This experiment aims to determine the purity of soda ash (Na2CO3) and similar samples using the double-indicator titration. The experiment also aims to understand the concept of titrimetric methods which include a...