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Overview:
When two aqueous solutions of ionic compounds are combined, a solid precipitate may form.
This occurs when a positive cation from one solution and a negative anion from the other solution form an insoluble compound. The attraction between the oppositely charged ions is stronger than the attraction of the individual ions to the polar water molecules, the solution's solvent. The result is a solid precipitate that rapidly comes out of solution.
For example, when solutions of silver nitrate, AgNO3, and sodium chloride, NaCl are combined, a double displacement reaction occurs and a white precipitate, AgCl, immediately forms:
AgNO3 (aq) + NaCl(aq) → AgCl(s) + NaNO3 (aq)
The net ionic equation, which removes the un-reacting spectator ions, shows more clearly the ions of interest:
Ag+(aq) + Cl-(aq) → AgCl(s)
If no insoluble combination between anions and cations exist, no precipitate will form. Instead, all ions remain in solution and no reaction occurs.
In this lab you will use your knowledge of precipitation tables to predict precipitation reactions. Examine the lists of solutions you will be using for this experiment. You will be mixing solutions from Set A with Set B. Which combinations do you predict will result in a precipitate? Record your predictions. You will then test your predictions by combining pairs of solutions to see if a precipitate forms.
Additionally you may be asked to prepare the standard 0.10 M solutions used for this lab. Your teacher may have you do this in advance of the precipitation tests.
Purpose
- To predict precipitation reactions.
- To observe a variety of precipitation reactions
- To write net ionic equations for precipitation reactions
- To prepare 0.10 M standard solutions
Safety
- Follow general lab safety rules for this experiment.
Equipment and Materials
- clear acetate overhead sheet or spot plate
- grease pencil to draw a grid on acetate sheet
- solutions as assigned by your teacher. You may have any or all of the following 0.10 M solutions:
Set A |
Set B |
sodium nitrate, NaNO3 potassium nitrate, KNO3 silver nitrate, AgNO3 ammonium nitrate, NH4NO3 lead(II) nitrate, Pb(NO3)2 calcium nitrate, Ca(NO3)2 magnesium nitrate, Mg(NO3)2 barium nitrate, Ba(NO3)2 copper(II) nitrate, Cu(NO3)2 iron(III) nitrate, Fe(NO3)3
|
sodium chloride, NaCl sodium hydroxide, NaOH sodium bromide, NaBr sodium sulfide, Na2S sodium iodide, NaI sodium phosphate, Na3PO4 sodium sulfate, Na2SO4 sodium carbonate, Na2CO3 |
Alternates
|
Alternates |
sodium acetate, NaC2H3O2 zinc acetate, Zn(C2H3O2)2
|
potassium carbonate, K2CO3 potassium phosphate, K3PO4 ammonium sulfate, (NH4)2SO4 |
Procedure
- See the print versions of this lab for full details