Solving Ksp Lab Errors: CaSO4 Calculation Methods

[reubend]

Hi, We did a lab the other day involving the calculation of Ksp values.

Objective of the lab was to calc the Ksp of CaSO4 by several methods and to determine which method would give the most consistent/accurate value for the solubility product constant.

Heres what we did:

A) 1. Filter 100.0 mL of saturated CaSO4 solution into a beaker.
2. Add 1.00 mL of 0.10 mol/L HCl solution and warm the soution to near boiling.
3. Add 10.0 mL of a 0.20 mol/L BaCl2 solution with stirring. Cover and set aside for 24hr.
4. Filter the mixture and collect precipitate.
5. Dry precipiate and mass.

B) repeat A but omit the addition of acid and heating. Also filter the precipitate right after reaction occurs.

C) 1. Mix 20.0 ml of .50 mol/L CaCl2 solution with 20.0 mL of .50 mol/L Na2SO4 solution.
2. Add 5.0 mL of .10 mol/L HCl and dilute to 500 mL with distiled water.
3. Filter the mixture and collect precipitate.
4. Dry precipiate and mass.

D) repeat C but omit the addition of acid.

I need help thinking of good errors that occurred whille conductiong the experiament and why our results would be off. Thanks a lot guys, this is my first time here and it seams like a nice community.

 

[chem_tr]

Welcome to the forum.

I think that gravimetric determination by means of precipitation with barium ions will give the best method for quantitative analysis of sulfate-containing products indirectly. Here, it seems that A is better than B; because filtering immediately may produce negative errors to your experiment. C is better than D and in my opinion, also better than A and B. In addition, C will give a more complete precipitation since we don't know if the added barium ions will be enough or not (you stated that 100 mL of saturated calcium sulfate is processed). Addition of acid will catalyze the reaction, I suppose. More importantly, it will increase the ionic "intensity" of the solution, and it helps precipitation more complete than not-HCl-added trial. We use the same principle in extractions of organic materials; we add an excess of NaCl solution to the organic phase to prevent aqueous solubility.

Hope these will help you deciding which method is the best.

 

[reubend]

Thanks a lot, that really helps.

I need a few errors that could have occurred such as the soloutions could have hydrated causing the concentrations to be incorrect..etc. I am having a hard time thinking of more.