Double Replacement Reactions
Mini-Lab
As previously discussed, double replacement reactions often involve the production
of a precipitate (solid) as a result of the reaction. In this lab, you will use the solubility
rules from your notes to help determine the products (as well as their physical states)
of a series of possible double replacement reactions.
Equipment - well plate
Procedure
1. Set up a 7 x 7 grid. You will record your observations of the various chemical
combinations in this grid in order to decide which ones actually underwent reactions.
Label each column and row with the chemical formulas to be used in the lab.
2. Go to your lab station and obtain the 6 x 4 well plate. Clean it out with tap water and
then dry it.
3. The various solutions are located at the middle of each lab bench throughout the lab.
Take your well plate to one of these solutions (it doesn’t matter which one you start
with) and use the large dropper or dropper bottle to partially fill six wells only covering
the bottom of the well plate is necessary. Then go to the other six solutions and place a
roughly equal amount of each solution into one of the six wells. You may need to use a
toothpick to gently stir the solutions together in order to produce the clearest results.
4. Return to your grid and jot down any observations. If no change is observed then
write “no rxn.” in the appropriate grid square.
5. Go to each solution and repeat steps #3 and #4 until all possible combinations have
been tried. Rinse out your well plate once you are done (all resulting solutions and
precipitates may safely go down the drain).
Conclusions & Analysis
1. For each reaction that you observed write down the balanced chemical equation. Be
sure to include all physical states.
2. To more clearly show what is happening in a reaction we often write what are called
ionic and net ionic equations. For double replacement reactions this involves taking a
regular balanced equation and performing the following steps:
-
Rewrite all (aq) salts as separate ions
Ex. 2 Na2SO4 (aq) would become 4 Na+ + 2 SO4-2
-
Keep all solid precipitates as together, since it is not split up into its ions in
solution
Ex. 2 Ca(OH)2 (s) would stay 2 Ca(OH)2
This results in what is called an ionic equation.
- Any ions that appear on both sides of the reaction arrow (spectator ions) are
eliminated; whatever still remains is rewritten
This results in what is called the net ionic equation.
Perform these steps for any 5 of the reactions from #1.
3. A specific category of double displacement reactions is that of neutralization
reactions. In these types of reactions an acid is reacted with a base. Predict the
products of the following neutralization reactions and then use them to come up with
a general pattern that these reactions all follow.
NaOH (aq) + HCl (aq) ?
Mg(OH)2 (aq) + H2SO4 (aq) ?
KOH (aq) + H3PO4 (aq) ?
Scoring Summary
Organization
- neatly organized observations U / A
- observed lab procedure
_____ (2)
Precision/Accuracy
- correctly expressed equations (#1) _____ (10)
Conclusions & Analysis
- ionic & net ionic equations
_____ (5)
- acid/base reactions (#3)
_____ (3)