Precipitation Reactions and Ionic Equations

Chemistry                                                                                            GIA 8-3

Unit: Solutions and Solubility                                                              Reading: Chapter 18

Working Mode: Lab Groups. Follow the procedure below, answer the questions and write the chemical equations as requested.  Submit your observations and equations on an attached sheet.

Learning Objectives:  To recognize a precipitation reaction, to predict a precipitation reaction based on solubility chart, and to write overall, total and net ionic equations for these reactions.

Equipment and Materials:

• clear, acetate sheet as reaction surface

• droppers containing the following solutions: Na₂CO₃, Na₂SO₄, NaCl, NaOH, KI, CaCl₂, ZnCl₂, Pb(NO₃)₂, FeCl₃, Na₃PO₄, MgSO₄, CuSO₄, AgNO₃.

Procedure 1: Combine 1 or 2 drops of each of the following solutions on the reaction surface sheet. (Be careful not to touch the tips of the pipets to other solutions.)

a.      Pb(NO₃)₂ & KI

b.     Na₂CO₃ & CaCl₂

c.      MgSO₄ & Na₃PO₄

d.     ZnCl₂ & MgSO₄

Questions for Procedure 1:

1. Indicate which combinations of drops resulted in a reaction.

2. Write the overall balanced equations for these reactions (include the states).

3. Write the total ionic equations for each of these reactions.

4. Circle the spectator ions.

5. Write the net ionic equations.

Procedure 2:  Consulting your solubility chart determine two reactant solutions that would produce the following precipitates.  Then test your hypothesis.

a.      AgCl

b.     Ca₃(PO₄)₂

Question for Procedure 2:

1. Write the balanced overall, total ionic and net ionic equations for your reactions above.

2. Suppose you wanted to separate a mixture of Zn²⁺, Na⁺ and Pb²⁺ ions.  Which solutions, (and in what sequence) would you use to do this?

Clean-up: Return all solutions to the appropriate beakers.  Use a paper towel to mop up the solutions from the acetate sheet.  Throw away the paper towel.  Apply distilled water to rinse the sheet a couple of times, and then dry it off with a paper towel.  Wash your hands.