Solubility Lesson 3 Separating Ions

1. Solubility Lesson 3 Separating Ions

2. Basic idea • You have an aqueous solution that contains ions. • You want to separate the ions. • Looking at the Solubility Table, you add an ion to your solution that you KNOW will form a precipitate with only one of your existing ions ( low solubility ) • After precipitation, you use filtration to remove the ppt. • Repeat until you separate the ions you want.

3. Separating positive ions

4. Positive ions react with negative ions to give a precipitate if they have low solubility. A precipitate can be separated from a solution by filtration. The precipitate will be on the filter paper while the soluble ions will go through. To separate ions; one ion must be low solubility and all others high.

5. Separating Positive Ions 1. Separate Ba2+ & Pb2+ Remember, if you want to form a ppt, you want to look at the ‘low solubility’ side because it means a ppt will form! Look at your “Solubility Table" and start with adding Cl- first

6. Ba2+ 1st add Cl-, it reacts with Pb2+ (low) forming a ppt 2nd add SO42-, it reacts with Ba2+ (low) forming a ppt.

7. NaCl Cl- Na+ Pb2+ Ba2+ PbCl2 Filter

8. Separating Positive Ions 1. Separate Ba2+ & Pb2+ i. Add NaCl Filter out PbCl2(s) Cl-does not exist on its own Add NaCl because it is soluble- always use Na+for negative ions Pb2+ + 2Cl- PbCl2(s) ii. Add Na2SO4 Filter out BaSO4(s) Ba2+ + SO42- BaSO4(s)

9. Na2SO4 SO4-2 Na+ Ba2+ BaSO4 Filter

11. Separating Positive Ions 2. Separate Cu2+, Mg2+ & Sr2+

12. Cu2+ Sr2+ Cu2+ Mg2+ Mg2+ Mg2+ Cu2+

13. Separating Positive Ions 2. Separate Cu2+, Mg2+ & Sr2+ i. Add Na2SO4 Filter out SrSO4(s) Sr2+ + SO42- SrSO4(s) SO42-does not exist on its own Add Na2SO4 because it is soluble- always use Na+for negative ions ii. Add Na2S Filter out CuS(s) Cu2+ + S2- CuS(s) iii. Add NaOH Filter out Mg(OH)2(s) Mg2+ + 2OH- Mg(OH)2(s)

15. Separating Negative Ions

16. Separating Negative Ions On “Solubility table” start from bottom working your way up- so start with negative ion on the bottom first. 3. Separate Cl- & OH- Start with OH- because it is on bottom of Solubility Table. Look for a cation/positive ion that is low with OH- (forms ppt) and high with Cl- ( doesn’t form ppt)

17. Ba2+ Look for a cation that is low withwith Cl- Look for a cation that is low with OH-and high with Cl-. Ba2+ Remove the bottom negative ion first by adding a positive cation.

18. Separating Negative Ions 3. Separate Cl- & OH- i.Ba2+works so add Ba(NO3)2and filteroutBa(OH)2(s) Ba2+ + 2OH- Ba(OH)2(s) Ba2+does not exist on its own Add Ba(NO3)2because it is soluble- always use NO3-to pair with positive ions ii.Add Ag+as AgNO3 and filter out AgCl(s) Ag+ + Cl- AgCl(s)

19. Separating Negative Ions 4. Separate Cl- S2- CO32-

20. Look for a cation that is low withwith Cl- Look for a cation that is low withS2-and high with Cl- Zn2+ Look for a cation that forms a ppt with only CO32- (high with Cl- and S2- ) Ba2+

21. Separating Negative Ions 4. Separate Cl- S2- CO32- i.Ba2+works so add Ba(NO3)2and filteroutBaCO3(s) Ba2+ + CO32- BaCO3(s) Ba2+does not exist on its own Add Ba(NO3)2because it is soluble- always use NO3-to pair with positive ions ii.Add Zn2+as Zn(NO3)2 and filter out ZnS(s) Zn2+ + S2- ZnS(s) iii. Add Ag+as AgNO3 and filter out AgCl(s) Ag+ + Cl- AgCl(s)

22. Summary Separating Positive Ion • Look at solubility table starting with Cl, choose a negative ion (Cl or otherwise) that can precipitate only ONE of the ions you have - Filter out the resulting precipitate and repeat!

23. Summary Separating Negative Ions • Look at solubility table starting from bottom, choose a positive ion that can precipitate only ONE of the ions you have. - Filter out the resulting precipitate and repeat!

24. Summary You may want to create a table to help you! Practice: Page90 #’s 28,29,30,35,36