Glencoe Chapter 10
Experiment: 
Precipitation Reactions

Introduction:

Many ionic compounds dissociate in water to produce positive and negative ions.  Other ionic compounds barely dissolve in water.  When two ionic compounds (when dissolved in water) are combined, a double-replacement reaction occurs which results in (1) all products staying in solution or (2) a compound precipitates out of solution.

What is a precipitate?  A precipitate an ionic compound which comes out of solution as a solid substance when two aqueous ionic compounds are mixed.  

Remember that in reactions such as these, you can often have "spectator" ions - these are ions which are present both in the solution (before mixing) and after the solutions have been mixed.  In other words, a spectator ion just "sits around" looking at what is going on around them ... they don't get involved in the "business" end of the reaction.   A net ionic equation represents the ionic equation without the spectator ions.

In this experiment, you will mix solutions of 8 different soluble ionic compounds, two at a time, and observe which combinations form precipitates.  You will identify which combinations form precipitates.  For these precipitate reactions, you will write ionic and net ionic equations.  

Materials:

• Eight compounds dissolved in water:
  • ammonium sulfate
  • calcium chloride
  • sodium hydroxide
  • lead nitrate
  • silver nitrate
  • potassium carbonate
  • copper(II) acetate
  • hydrochloric acid
• dropper bottles
• distilled water
• plastic sheets

Data Table:

• Click here to get copy of the data table you will need.  PRINT OUT!
• In the lab, be sure to use blue or black PEN (NO PENCIL) when you complete this data table.  NEVER WHITE-OUT data.  Enter data carefully so that you make no mistakes.  

Procedure:

1. Use the plastic sheets provided.
2. Rinse plastic sheet with distilled water and dry off with a paper towel.
3. Place 3 drops of one of the solutions into the appropriate square.  Add 3 drops of a second solution.  BE CAREFUL NOT TO TOUCH THE TIP OF THE SECOND DROPPER INTO THE FIRST SOLUTION ON THE SQUARE.  Otherwise, you will contaminate the second solution bottle!
4. Wait about 10 seconds and record the presence of a precipitate.  You will record ONLY the places where precipitates occurred onto your data table!  Follow the directions at the top of the DATA TABLE.
5. HELPFUL HINT: You may "check off" each box as you mix solutions - so you don't get confused as to the solutions you have completed.  Make each ümark tiny -- this is for your record-keeping only.
6. Repeat steps 3-4 for each pair of solutions.
7. When done, thoroughly rinse the plastic sheet again with distilled water.  DRY THOROUGHLY with a paper towel before returning it up to the lab prep area.

Analysis:

From the data table, you will see where precipitates formed.  
COMPLETE THE WORK BELOW ONLY FOR THOSE REACTIONS WHERE PRECIPITATES FORMED (both partial PPT and PPT) !!!  
Do the analysis part of this lab on separate paper.  You will staple your work behind your data table which you will turn in.

• NUMBER EACH EQUATION WITH THE NUMBER LOCATED IN EACH SQUARE ON YOUR DATA TABLE.  (Failure to do this will result in loss of 1/2 credit for the lab.)
  1. Write the balanced double-replacement reaction.  Use your solubility table to determine WHICH compound precipitates out of solution - underline it.  
  2. Write ionic equations.
  3. Write net ionic equations.