AnalChem Postlab 4.docx - Stephanie Peak Lara Wolff Lab 4...

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Stephanie Peak Lara Wolff Lab 4. Volumetric Determination of Impure Sodium Carbonate Introduction In this experiment, a standardized solution of HCl will be used to titrate a solution that contains an unknown amount of sodium carbonate. 1 This is an acid-base reaction in which a salt, water, and CO 2 are produced as products of the reaction. 1 The HCl solution is standardized because accurate results from titration reactions can only truly be accomplished if the exact concentration of the volumetric solution is known. 2 Standardization implies that the titrant that is used in the titration procedure has a known concentration, which is achievable by titrating it against another solution with a known concentration. 2 The equivalence point in a titration is achieved when the number of moles of titrand is equivalent to the number of moles of the titrant. 3 This is determined via an indicator, which express different qualitative changes when this is reached in a titration. If the titration is mistakenly continued past the equivalence point, the titration’s end point will be reached. This occurs when the moles of titrant are more than the moles of titrand, as shown with the presence of the indicator as well. 4 Two indicators are used in this experiment, one of them being phenolphthalein, which is used for neutralizing HCl and sodium carbonate into NaHCO 3 and NaCl. 1 The equivalence point of this titration is reached when the solution changes in color from bright pink to clear. The other indicator, bromocresol green, is used to neutralize HCl and NaHCO 3 . This indicator is initially blue, indicating the presence of soda ash. This color change
proceeds to green at the equivalence point and continues to yellow at the end pont. 1 The analyte solution is boiled after reaching the equivalence point because it is not the real equivalence point of the reaction. Boiling the solution removes the carbon dioxide in the solution, returning the

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