Thermodynamics of the Dissolution Borax

Thermodynamics of the Dissolution of Borax Lina Jawadi Objectives * psychoanalyze a system of salt and water solution. * Determining a mixed bag of important thermodynamics quantities from the solvability information at various temperatures. Background The salt and water solution in this experiment has relatively simple solubility equilibrium of borax in water. Na2B4O7 . 10 H2O 2Na + + B4O5(OH)42- + 8H2O This reaction is an equilibrium treat and 8 water molecules from the hydrated salt are lost to the reaction medium. The equilibrium unalterable expression for this reaction isK = Na+2 B4O5(OH)42- H2O8 Na2B4O7 . 10 H2O In this experiment we will always make for certain there is several(prenominal) lusty borax remaining in the seek mixture before removing about of it to analyze it. Therefore, we can assume that the concentration of solid borax is invariable. In jibeition, the water molecules which were originally part of the boraxs crystalline matrix is lost to the sampl e mixture however, it doesnt significantly affect the concentration of the water. The equilibrium constant expression can now be simplified to become K = Na+2 B4O5(OH)42-The first equilibrium expression and the balanced solubility equilibrium reaction allow us to express twain borate ion or sodium ion in terms of the other. So, it is possible to determine the constant in terms of either ion. After substituting borax ion in get into of the sodium ion, (Na+ = 2 B4O5(OH)42- , K = (2 B4O5(OH)42- )2 * B4O5(OH)42- ) we get K = 4 B4O5(OH)42-3 . Finding the concentration of borate ion in any(prenominal) sample at any given temperature gives us the solubility crop at that temperature. Equipment * 5mL pipet * Test tubings * Marker * Hot plate * 250 mL beaker * Flask Electric balance Procedure 1. Using the pipet make for 5mL of distilled water to 10 test tubes. 2. Mark the level with the marker and move the water out. Mark the test tube with the assigned temperature. 3. Weigh 30-32g of solid sodium borate decahydrate (borax) in a 250 mL beaker and then add one hundred fifty mL of water. 4. Place the mixture on a hot plate, yet dont allow its temperature to exceed 50oC. 5. After all the borax dissolves, add more and let the temperature reach 45oC. 6. Once it starts slightly exceeding 45oC, pip it from the hot plate and place instead a beaker filled with cl mL of distilled water. . Continue stirring the mixture until it reaches the desired temperature. 8. Quickly pullulate 5 mL of the mixture in two test tube without transferring any solid borax. (record the temperature before and after the transfer. ) 9. When the water bath reaches 45oC, place the test tube in it until precipitation of borax has dissolved. 10. In a flask with 50-75 mL of water and 10 drops of bromocresol green indicator, add 125 mL of the borax solution. 11. Before titrating the borax with acid make sure that it has a blue color.Using burette filled with 50 mL oh HCl, add the acid to the bora x until it reaches the endpoint, which is when the solution turns from a blue color to a yellow. Record the initial and final volume. (For calculations acquire the moles of borax using the volume of HCl and its molarity. Then find the solubility product constant and plot the ksp vs. (1/t) graph and from it obtain the values of ? H and ? S. Make sure the temperature is in kelvin when doing the calculations. Finally, find the value of ? G using both equations and plot the ? G vs. time graph. )