CHE 113 Lab Calculating Solubility and Ksp Values PDF

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Lab Report for CHE 113 Calculating Solubility and Ksp Values....

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CHE 113 11-11-2020 Calculating Solubility and Ksp Values Introduction The purpose of this experiment is to determine the Ksp value of Calcium hydroxide. In order to find the Ksp value, the hydroxide concentration will have to be determined in the slightly soluble salt concentration set up during the experiment. The saturated solution consists of the maximum amount of solute that should dissolve in the solution. Elements such as pH and temperature can affect the solubility of certain mixtures. Temperature can change very quickly in a solution so it is crucial that the solution is made with plenty of solute so that the maximum amount dissolved can be reached. After the solution has been dissolved, it has to be filtered to remove any excess solute still remaining. If the excess remains the equilibrium will be thrown off and more HCl will be needed to make the reaction reach it’s true equilibrium. A primary standard will be used to standardize the HCl concentration in the experiment in order to get an accurate Ksp value. This standard is made of sodium carbonate and gives the following reaction: Na2CO3 + 2 HCl → CO2 + H2O + 2 NaCl (French et al. 98) Once the concentration of HCl has been found the concentration of hydroxide can be found. Knowing these concentration will give the Ksp for the following reaction: 2 HCl + Ca(OH)2 → CaCl2 + 2 H2O (French et al. 98)

Methods 1. A saturated solution with Ca(OH)2 had already been made for the students in the lab Standardization of HCl 2. Obtain about 0.200g Na2CO3 and record mass of three samples 3. Prepare three Na2CO3 solutions with about 20mL DI water in a 100mL beaker. (stir until the solution is completely dissolved. 4. Obtain buffer solutions with pH 4 and pH 10 (only use enough to cover the tip of the probe used) 5. Set up ring stand with clamp, burette, pH probe, and drop counter for the titrations. 6. Set up MeasureNet station and calibrate 7. Calibrate with the pH 4 buffer first, once stable hit “enter”. Rinse probe and repeat with pH 10 buffer. 8. Add 0.2 M HCl to burette and record initial volume. Burette doesn’t need to be completely filled. 9. Start titration and watch for equivalence point on MeasureNet station. Swirl while mixing the solution for a smoother curve 10. Stop MeasureNet and record the final volume of HCl burette and enter the volume into MeasureNet. Save as file 001 and check graph with TA. 11. Repeat steps above for sample 002 and 003

Determination of Hydroxide Concentration

12. Filtered Ca(OH)2 solution had been prepared for students in the lab. 13. Collect pH 4 and pH 10 buffers to calibrate again 14. Calibrate MeasureNet 15. Measure approximately 25 mL of Ca(OH)2 solution and place into 100 mL beaker and record the exact volume 16. Fill burette with 0.2 M HCl and record exact initial volume 17. Titrate Ca(OH)2 sample while evenly swirling beaker, once titration is complete stop MeasureNet and record final volume of HCl. Save as 004. 18. Repeat steps above for file 005 and 006. 19. Clean all supplies and put back where they came from.

Discussion The purpose of this lab was to determine the Ksp value of Calcium Hydroxide. This was achieved during the experiment by preparing a saturated solution by using a primary standard to find the hydroxide concentration and a slightly soluble salt. The titrations performed in the lab gave an average HCl molarity of 1.49 M and an average Ca(OH)2 molarity of 0.141 M. Once the average molarity of Ca(OH)2 was found, it was used to determine the Ca2+ and this value was 0.141 M and the concentration of OH- was 0.282 M. With these numbers the Ksp was determined to be 0.0112. The accepted Ksp value is 6.5 E -6 this gives me a percent error of 172,207%. The results of my experiment did not support my hypothesis as seen by the extremely high percent error. This high error percentage shows that there were some major errors during the lab and because of this the Ksp was not accurately determined.

There were potential errors in this lab. First potential error could have been if someone had shaken the premade saturated Ca(OH)2 solution. This would have disrupted the solution and thrown everyone’s results off that used the specific solution. This could easily be avoided by carefully pouring the solution into the beaker and not moving the solution to another location. A second potential source of error could be not using enough HCl in the burette. Once the HCl ran out if the equivalency points had not been reached the air around could go into the beaker and if MeasureNet had not been stopped yet, it would change the results drastically. This can be avoided by making sure enough HCl was in the burette before starting the titration. Lastly, a third potential error could be from not using enough or using too much Na2CO3. If the Na2CO3 didn’t dissolve completely it would change the results of the equivalence points measured. If there was too little then the equivalency points would change way too quickly than expected. This is easily avoided by carefully measuring how much Na2CO3 was used before dissolving with DI water.

Conclusion This lab has taught me a lot more about titrations and that I need much more practice when it comes to titrating solutions. Although I messed up severely during the lab I still learned how to determine a Ksp value. It taught me how important little things can be when trying to titrate or making solutions and how long it might take for these solutions to develop. This applies to real life because some of us make saturated solutions almost daily. If someone makes sweet tea, Kool-aid, and many other types of drinks and foods. They are all making different saturated solutions.

Works Cited French, April N., Allison Soult, Stephen Testa, Meral Savas, Francois Botha, Carolyn Brock, Charles Griffith, Darla Hood, Robert Kiser, Penny O’Conner, William Plucknett, Donald Sands, Diane Vance, William Wagner. “Solubility of Calcium Hydroxide.” Chem 113 General Chemistry II Lab Manual. Plymouth, M: Hayden-Mcneil, 2018. 97-100. Web. 11 November 2020. https://www3.chem21labs.com/labfiles/36194_43_Exp%2017_FrenchA %2021871%20W20..pdf?rf=9994....