Double Replacement Reactions
Chemical reactions can occur between ionic compounds that are dissolved in aqueous solution. When
ionic compounds dissolve in water, they dissociate into separate cations and anions because they are attracted
to the polar water molecules. These ions move freely throughout the solution. As the cations and anions from
the original two compounds move about, they may recombine to form two new compounds as in the equation
below.
AB + CD
CB + AD
This type of chemical reaction is called a double replacement reaction. In the double replacement reactions
studied in this lab, at least one of the new compounds formed will not be soluble in the aqueous solution and
will form a solid. The solid, called a precipitate, will sink to the bottom of the reaction vessel or will give the
mixture a cloudy appearance.
In this lab you will mix together solutions of ionic compounds and observe the appearance of the
precipitate. You will determine the identity of the precipitate(s) using the attached solubility rules. (These
rules should be added to your lab book appendix.) You will then construct a balanced chemical equation and a
balanced ionic equation for each double replacement reaction. Use the phase subscripts (aq) and (s) to indicate
the soluble and insoluble products respectively.
For example, let us say we are combining aqueous solutions of magnesium chloride and silver nitrate. T
Follow the steps below for writing the equations and identifying precipitates.
1. Write the word equation. Determine products by switching cation/anion partners:
magnesium chloride + silver nitrate
silver chloride + magnesium nitrate
2. For the chemical equation, write the correct formulas of the reactants and products. Add phases. Reactants
will always be (aq). Use the solubility rules to determine whether the products are soluble (aq) or insoluble
(s).
MgCl2(aq) + AgNO3(aq)
Mg(NO3)2(aq) + AgCl(s)
According to solubility rule 2, magnesium nitrate is soluble. According to rule 6, silver chloride is not soluble and must therefore be
the precipitate.
3. Then you need to balance the equation using coefficients. Do Not change the formulas of the compounds in
order to balance the equation!! Remember to include phases.
MgCl2(aq) + 2AgNO3(aq)
Mg(NO3)2(aq) + 2AgCl(s)
4. Write and balance an ionic equation for each reaction by dissociating all aqueous compounds. The number
of atoms of each type and total charges should be the same on both sides of the equation. Specify solid
phases.
Mg2+ + Cl
5.
+ Ag+ + NO3
AgCl(s) + Mg2+ + NO3
Eliminate all spectator ions (ions that remain dissociated on both sides of equation) to write the net ionic
equation.
Mg2+ + Cl + Ag+ + NO3
AgCl(s) + Mg2+ + NO3
net ionic eqn: Ag+ + Cl-
AgCl(s)
Procedure:
For each of the 7 pairs of compounds listed, combine 5 drops of each solution in a spot plate well and record
your observations.
Be careful not to contaminate the dropper tips by allowing them to touch the solutions in the spot plate.
Replace the original cap on the dropper bottle before obtaining the next solution. Do NOT place cap on
lab bench!
1. calcium acetate and copper (II) sulfate
2. lithium carbonate and iron (III) nitrate
3. sodium iodide and silver nitrate
4. lead (II) nitrate and sodium iodide
5. copper (II) sulfate and sodium hydroxide
6. silver nitrate and lithium carbonate
7. iron (III) nitrate and sodium hydroxide
Prelab Assignment:
 Write title, purpose and flow chart procedure for this lab in your lab notebook.
 Construct a data table in your lab book that shows formulas for each pair of compounds combined and a
space for observations to be recorded.
 You are expected to be familiar with the boldface terms in the first 3 paragraphs on page 1 of this lab
packet.
Lab Report:
For each of the 7 reactions include the following:
Word Equation – states correct name of each reactant and product
Chemical Equation -includes phase symbols to indicate the identity of the precipitate(s) – it is possible
that both products are precipitated. Be sure equation is balanced.
Ionic or Net Ionic Equation – balanced, with phases for all solids
No additional conclusion is required. Grade is heavily based upon the accuracy of your equations,
so write neatly, skip a line between each equation, and be accurate with formulas and balancing.