Analysis of Soda Ash and Volumetric Analysis of a Carbonate-Bicarbonate Mixture

1800 words 8 pages
Analysis of Soda Ash and Volumetric Analysis of a
Carbonate-Bicarbonate Mixture
Manalo, Ma. Cristina Joyce B.
Department of Chemical Engineering, Faculty of Engineering
University of Santo Tomas
Espana, Manila

A. Abstract

Crude sodium bicarbonate or commonly known as soda ash may contain amounts of impurities like chlorides and hydroxides. The total acid neutralizing capacity of a soda ash sample, its alkalinity value, was stated in terms of mass of sodium carbonate. In doing so, any sodium hydrogen carbonate present in the sample was converted to its equivalent neutralizing capacity in terms of sodium carbonate. A mass of the impure sample was dissolved and diluted in distilled water. 3 drops of indicator was mixed and the solution
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20 mL of NaOH was used in trials 1 and 2. The volume of HCl used in two trials to color the solution light pink or to reach the endpoint was 15.4 mL and 16.0 mL respectively. The concentration of NaOH which was taken from the last experiment was 0.0938 mol/L. This gave an average concentration 0.1146 M HCl.
Alkalinity of Soda Ash | Trial 1 | Trial 2 | Mass of Sample | 0.3337 g | 0.3337 g | Final Volume of HCl | 4.8 mL | 4.9 mL | Initial Volume of HCl | 0.0 mL | 0.0 mL | Volume of HCl used | 4.8 mL | 4.9 mL | Mass of Na2CO3 | 0.150 g | 0.153 g | % Alkalinity | 44.82% | 45.75% | Ave % Alkalinity | 45.275% | % Error | 19.17 % |

A 0.3337 g of soda ash sample was used. In trial 1, 4.8 mL of HCl was used to reach the endpoint and in trial 2, 4.9 mL was used. Using the formula:

The mass of sodium carbonate was determined to be 0.150g and 0.153g in two trials. The average %alkalinity was computed to be 45. 275% using the formula:

It is preferable to titrate NaOH with standard HCl rather than the reverse process because NaOH reacts with CO2 to form the carbonate. This interferes with the end point. So putting a large amount of NaOH in a flask or beaker and stirring it will cause it to absorb CO2 from air.
Storing NaOH solutions are a problem for the same