Solubility Lesson 3 Separating Ions

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.

Separating positive ions

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.

Separating Positive Ions 1.SeparateBa 2+ &Pb 2+ Look at your “Solubility Table" and start with adding Cl - first Remember, if you want to form a ppt, you want to look at the ‘low solubility’ side because it means a ppt will form!

Ba 2+ 1 st add Cl -, it reacts with Pb 2+ (low) forming a ppt 2 nd add SO 4 2-, it reacts with Ba 2+ (low) forming a ppt.

Pb 2+ Ba 2+ NaCl Na + Cl - PbCl 2 Filter

Separating Positive Ions Cl - does not exist on its own Add NaCl because it is soluble- always use Na + for negative ions 1.SeparateBa 2+ &Pb 2+ i.AddNaClFilter out PbCl 2(s) Pb 2+ +2Cl -  PbCl 2(s) ii.AddNa 2 SO 4 Filter out BaSO 4(s) Ba 2+ +SO 4 2-  BaSO 4(s)

Ba 2+ Na 2 SO 4 Na + SO 4 -2 BaSO 4 Filter

Cl SO 4 Ba------ppt Pb ppt

Separating Positive Ions 2.SeparateCu 2+,Mg 2+ &Sr 2+

Cu 2+ Mg 2+ Sr 2+ Cu 2+ Mg 2+ Cu 2+ Mg 2+

Separating Positive Ions 2.SeparateCu 2+,Mg 2+ &Sr 2+ i.AddNa 2 SO 4 Filter out SrSO 4(s) Sr 2+ +SO 4 2-  SrSO 4(s) ii.AddNa 2 SFilter out CuS (s) Cu 2+ +S 2-  CuS (s) iii.AddNaOHFilter out Mg(OH) 2(s) Mg 2+ +2OH -  Mg(OH) 2(s) SO 4 2- does not exist on its own Add Na 2 SO 4 because it is soluble- always use Na + for negative ions

SO 4 SOH Cu----ppt Mg---- ppt Srppt----

Separating Negative Ions

On “Solubility table” start from bottom working your way up- so start with negative ion on the bottom first. 3.SeparateCl - &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)

Ba 2+ Remove the bottom negative ion first by adding a positive cation. Look for a cation that is low with OH - and high with Cl -. Look for a cation that is low with with Cl -

Separating Negative Ions 3.SeparateCl - &OH - ii.Add Ag + as AgNO 3 and filter out AgCl (s) Ag + +Cl -  AgCl (s) Ba 2+ does not exist on its own Add Ba(NO 3 ) 2 because it is soluble- always use NO 3 - to pair with positive ions i.Ba 2+ works so add Ba(NO 3 ) 2 and filter out Ba(OH) 2(s) Ba 2+ +2OH -  Ba(OH) 2(s)

Separating Negative Ions 4.SeparateCl - S 2- CO 3 2-

Ba 2+ Zn 2+ Look for a cation that forms a ppt with only CO 3 2- (high with Cl - and S 2- ) Look for a cation that is low with S 2- and high with Cl - Look for a cation that is low with with Cl -

Separating Negative Ions 4.SeparateCl - S 2- CO 3 2- i.Ba 2+ works so add Ba(NO 3 ) 2 and filter out BaCO 3(s) Ba 2+ +CO 3 2-  BaCO 3(s) ii.Add Zn 2+ as Zn(NO 3 ) 2 and filter out ZnS (s) Zn 2+ +S 2-  ZnS (s) iii.Add Ag + as AgNO 3 and filter out AgCl (s) Ag + +Cl -  AgCl (s) Ba 2+ does not exist on its own Add Ba(NO 3 ) 2 because it is soluble- always use NO 3 - to pair with positive ions

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!

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!

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