DETERMINATION OF SODA ASH PURITY
Standardization of HCl In the fume hood, prepare a solution of HCl that is about 0.1 M by dissolving 10 mL of conc. HCl in about 1 L of DI water. Dry about 1.5 g of primary standard sodium carbonate for 1 h at 160oC, cool in your desiccator, and using an analytical balance weigh at least 5 samples into separate 250 mL conical flasks. Be sure to choose sample sizes that will require between 30 and 50 mL of titrant. Add 100-125 mL of DI water and 2 drops of modified methyl orange indicator to each flask. Titrate the sample slowly (0.5 mL/s) until the indicator changes color from green to gray (almost colorless.) [NOTE: This is a relatively gradual change. If the solution appears purple you have titrated too far - discard that sample and obtain another.] Record the titrated volume in your lab notebook (Don't forget to rinse the inside of your flask!). Calculate the molarity of the HCl solution using the volume of HCl, the mass and purity of the standard sodium carbonate, the molecular weight of sodium carbonate (105.99), and the balanced chemical equation for the reaction between sodium carbonate and HCl.
Determination of Soda Ash Purity Dry your unknown for at least 1 h at 160oC. After cooling your unknown in your desiccator use an analytical balance to weigh 5 samples into separate 250 mL conical flasks. Again, be sure to choose sample sizes that will require between 30 and 50 mL of titrant. From this point repeat the procedure used to standardize your HCl. Calculate the percent purity of soda ash (sodium carbonate) present in your sample.