TitrationofSodiumCarbonatewithHydrochloricAcid.docVIP

PAGE 1 PAGE 8 Sodium Carbonate Titration web version 02-03 Titration of Sodium Carbonate with Hydrochloric Acid NAME:________________________________________ PERIOD:___________ Prelab 1. Write an equation, which correctly represents solid sodium carbonate dissolving in water. 2. During the titration of sodium carbonate with HCl, the dissolved carbonate ion will exist in three different forms; CO3-2, HCO3-1, and H2CO3. During which part of the titration (initial, first equivalence point, or second equivalence point) will each form predominate. Explain your answer. 3. Why are two different indicators being used in this experiment? 4. Explain the difference between the terms endpoint and equivalence point? 5. Calculate the molarity (M) of HCl used in the titration of a 0.2239-g sample of sodium carbonate that required 39.01 mL of the titrant (HCl) to reach the second equivalence point. Titration of Sodium Carbonate with Hydrochloric Acid Objectives: In this experiment, a solution of Na2CO3 will be titrated with a solution of HCl. The pH of the solution will be monitored as the HCl is added with a pH probe attached to a CBL. The shape of the pH titration curve will be observed and the Kb values for the base will be determined. How closely the indicator color changes coincide with the equivalence points will be observed. Introduction: Carbonate ion, CO3-2, is a diprotic base, and shows the following ionization reactions in aqueous solution: CO3-2 (aq) + H2O (l) ? HCO3-1 (aq) + OH-1 (aq) HCO3-1 (aq) + H2O (l) ? H2CO3 (aq) + OH-1 (aq) The designation Kb1 refers to this being the first base ionization constant for CO3-2. CO3-2 should be recognized as the conjugate base of HCO3-1 and Kb1 equals Kw/Ka2 where Ka2 is the Ka for HCO3-1, which is also the second ionization constant for H2CO3. Likewise, Kb2 refers to the second base ionization constant for CO3-2. HCO3-1 should be recognized as