solubility lesson 3 separating ions
DESCRIPTION
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 ) - PowerPoint PPT PresentationTRANSCRIPT
SolubilityLesson 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. Separate Ba2+ & Pb2+
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!
Ba2+
1st add Cl-, it reacts with Pb2+ (low) forming a ppt
2nd add SO42-, it reacts with Ba2+ (low) forming a ppt.
Pb2+ Ba2+
NaCl
Na+ Cl-
PbCl2
Filter
Separating Positive Ions
Cl- does not existon its ownAdd NaCl becauseit is soluble- always use Na+ for negative ions
1. Separate Ba2+ & Pb2+
i. Add NaCl Filter out PbCl2(s)
Pb2+ + 2Cl- PbCl2(s)
ii. Add Na2SO4 Filter out BaSO4(s)
Ba2+ + SO42- BaSO4(s)
Ba2+
Na2SO4
Na+ SO4-2
BaSO4
Filter
Cl SO4
Ba ------ ppt
Pb ppt ppt
Separating Positive Ions
2. Separate Cu2+, Mg2+ & Sr2+
Cu2+ Mg2+ Sr2+
Cu2+ Mg2+
Cu2+
Mg2+
Separating Positive Ions
2. Separate Cu2+, Mg2+ & Sr2+
i. Add Na2SO4 Filter out SrSO4(s) Sr2+ + SO4
2- SrSO4(s)
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)
SO42- does not exist
on its ownAdd Na2SO4 becauseit is soluble- always use Na+ for negative ions
SO4 S OH
Cu ---- ppt ppt
Mg ---- ---- ppt
Sr ppt ---- ----
Separating Negative Ions
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)
Ba2+
Ba2+
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. Separate Cl- & OH-
ii. Add Ag+ as AgNO3 and filter out AgCl(s)
Ag+ + Cl- AgCl(s)
Ba2+ does not existon its ownAdd Ba(NO3)2 becauseit is soluble- always use NO3
- to pair with positive ions
i. Ba2+ works so add Ba(NO3)2 and filter out Ba(OH)2(s)
Ba2+ + 2OH- Ba(OH)2(s)
Separating Negative Ions 4. Separate Cl- S2- CO3
2-
Ba2+
Zn2+
Look for a cation that forms a ppt with only CO3
2- (high with Cl- and S2- )
Look for a cation that is low with S2- and high with Cl-
Look for a cation that is low with with Cl-
Separating Negative Ions 4. Separate Cl- S2- CO3
2-
i. Ba2+ works so add Ba(NO3)2 and filter out BaCO3(s)
Ba2+ + CO32- BaCO3(s)
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)
Ba2+ does not existon its ownAdd Ba(NO3)2 becauseit is soluble- always use NO3
- 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