Conductimetric Titration and Gravimetric Determination of a Precipitate Objective: * Measure the conductivity of the reaction between sulfuric acid and barium hydroxide * use conductivity values to determine equivalence point * measure mass of a product to determine equivalence point gravimetrically * calculate molar concentration of barium hydroxide solution Procedure: * First, combine 10. 0 mL of the Ba(OH)2 solution with 50 mL of distilled water. Then, measure out 60 mL of 0. 100 M H2SO4. Set up a conductivity probe and open programs by connecting to logger pro. After that, start to titrate with increments of 1. mL. Keep titrating with smaller increments until it is pretty close to the 100 microsiemens/cm mark. Calculate the lowest value. After that, record the volume as the equivalence point. Finally, filter and measure the mass of the barium sulfate precipitate. Data: | Trial 1| Trial 2| | | | Equivalence Point (mL)| 8. 0| 7. 6| | | | Mass of filter paper and precipitate (g)| | 1. 2417| | | | Mass of filter paper (g)| | 1. 0469| | | | Mass of precipitate (g)| | 0. 1948| | | | Molarity of H2SO4 (M)| 0. 100| 0. 100| | | | Calculations and graphs: * see last page for graph * Equations: * M = n/V Molar Mass = m/n * percent error = [|(experimental – actual)|/actual] • 100 1. 7. 6 mL| 1L| 0. 100mol| | 1000 mL| 1L| = 7. 6 • 10-4 mol 2. mol H2SO4 = mol Ba(OH)2 7. 6 • 10-4 mol Ba(OH)2| 0. 010 L | = 0. 076 M 3. 0. 1948 g BaSO4| 1 mol| | 233. 43 g| = 0. 0008351 mol BaSO4 4. mol BaSO4 = mol Ba(OH)2 0. 0008351 mol Ba(OH)2| 0. 010 L| = 0. 0835 M 5. (|0. 076 – 0. 100|)| 0. 100| * 100 = 24% (|0. 0835 – 0. 100|)| 0. 100| * 100 = 17% Discussion of Theory: * The concept performed in this lab was determining molar concentration of conductimetric titration and gravimetric determination of a precipitate.
When the base Ba(OH)2 solution reacted with the acid H2SO4 solution, a precipitate and water formed. The reactant ions reacted and decreased as more product formed. By measuring the conductivity throughout, the equivalence point was determined. With the equivalence point and the stoichiometric relationship, the molarity of barium hydroxide can be determined. Another way to calculate the molar concentration of barium hydroxide would be to calculate the number of moles of the insoluble barium sulfate by gravimetric determination. Data Analysis: 1. 7. 6 • 10-4 mol H2SO4 2. 0. 76 M Ba(OH)2 3. 0. 0008351 mol BaSO4 4. 0. 0835 M Ba(OH)2 5. Equivalence Point: 24% error, Gravimetric determination: 17% error. The gravimetric determination was more accurate because an exact amount of precipitate was formed. Conclusion: In this lab an attempt was made to determine the concentration of a Ba(OH)2 solution by using the conductimetrically determined equivalence point of the reaction between Ba(OH)2 and H2SO4 and by gravimetric determination. The molarity using the equivalence point was determined to be 0. 076 M, with a percent error of 24% (actual value was 0. 100 M).
The molarity using gravimetric determination was 0. 0835, an error of 17%. One possible error is the presence of bubbles in the buret. Bubbles would have caused the buret reading to be too high, resulting in a larger equivalence point. Another possible error deals with the colloidal nature of barium hydroxide due to its relatively low solubility. The colloidal barium hydroxide would make it more difficult for barium sulfate to precipitate out when reacting. Decreasing the amount of precipitate would make the molarity lower than the actual, and would also account for the error experienced in this lab.