Before doing this lab, you should read the chapter in your textbook dealing with writing net ionic equations and predicting products. The combination of this laboratory exercise and the information in that chapter coupled with your net ionic reaction writing lecture notes will start you on your way to being able to correctly predict the products of chemical reactions. You will find that acquiring this skill takes a considerable amount of practice and should be a part of your
AP Chemistry course throughout the academic year. You will have to use both your analytical skills as well as your observational skills to do well in this area of chemistry. This website will prove useful to you: http://dwb4.unl.edu/AP2/
The four broad types of chemical reactions we will be observing in this lab are as follows:
Precipitation reactions: A precipitation reaction is a reaction which produces a new compound which is not soluble in aqueous solution. These reactions are easy to observe, as the precipitate makes the previously clear solution become opaque or cloudy. By putting the drops of reagent you wish to mix on the line between black and white on your Reaction
Matrix chart, you should be able to observe the formation of any precipitate. In order to interpret the precipitate’s identity, it is necessary to know the solubility rules. The following rules are helpful:
™ All nitrates are soluble.
™ All Group(I) metal, ammonium (NH
4
+ ) and acetate (C
2
H
3
O
2
‒ ) compounds are soluble.
™ Most halide compounds are soluble except for those containing the “heavy metal bad guys” which are silver, mercury and lead.
™ Most sulfates are soluble except strontium, barium and calcium compounds.
™ Except for Group(I) and ammonium compounds, hydroxides, carbonates, and phosphates are insoluble.
Acid-Base reactions: An acid and a base react to produce a salt and water. Since many of the salts are soluble, there is no
visible reaction. This, however, does not mean that there is no reaction occurring. Be on the lookout for changes in pH!
In interpreting acid-base reactions, look also for ions which hydrolyze in water causing Brønsted acid-base reactions.
Ions that you would want to watch for would include C
2 they are the counterions of weak acids or bases.
H
3
O
2
‒ , HSO
3
‒ , SO
3
2 ‒ , CO
3
2 ‒ , HCO
3
‒ , S 2 ‒ , HS ‒ , NH
4
+ . Notice that
Also, look for Lewis acid-base reactions. Anything which is electron deficient, such as boron compounds or metal cations, will react with anything that has a lone pair of electrons, such as nitrogen or oxygen. While not dealt with directly in this lab, you should remember that acid anhydrides (non-metal oxides) and basic anhydrides (metal oxides) also fall into the acid-base category.
Redox reactions: The reactions which involve a transfer of electrons from one chemical species to another are oxidationreduction reactions (redox). These reactions include most composition, decomposition, and single replacement reactions as well as those that release a gas. They also include some other, more complex reactions. We will be looking for patterns in redox reactions more extensively later on in this course, for now you would be wise to be on the lookout for some widely used oxidizing and reducing agents. Suspect a redox reaction is taking place if the reactants include: MnO
MnO
2
, H
2
O
2
, Cr
2
O
7
2 ‒ , or HNO
3
4
‒ ,
(the strong “oxidizing acid”). When predicting products, remember that if one reactant is oxidized, another reactant must be reduced. Additionally, we refer to the reactant that is reduced as the oxidizing agent since it is causing the oxidation of the other reactant. The converse is also true.
Adapted by Carol Brown & René McCormick from Chemtreck: Small-Scale Experiments for General Chemistry laboratory protocol by Stephen Thompson.

Complexation reactions: Complexation reactions are related to acid-base reactions. In fact, they are Lewis acid-base reactions. Many metal cations gather ions or molecules (called ligands) around them to form a complex ion. Frequently the color and solubility properties of the complex ion differ from the original substance. If you start with a solid, and it dissolves, or if you have a vivid color change without the formation of a precipitate, you should suspect a complexation reaction. We will see complex ion formation primarily among the transition metals and Al 3+ compounds.
In this experiment, you will
• Perform a series of chemical reactions.
• Record observations for any reactant combinations that produce a visible chemical change.
•
•
Write a net ionic equation for any reactant combinations that produce a visible chemical change.
Use the observations recorded to identify a set of 5 unknown reagents.
A laminated Reaction Matrix Chart Solutions of the following bases:
NH
3
Goggles & aprons
and NaOH
A set of reagents as unknowns
Solutions of the following acids:
HCl, HNO
3
, H
2
SO
4
Litmus paper Solutions of the following salts:
Na
3
PO
4
Toothpicks for mixing
, Na
2
CO
3
, AgNO
3
, Pb(NO
3
BaCl
2
, AlCl
3
, KI, CuSO
4
)
2
, FeCl
3
,
Hand lens or magnifying glass if available
1.
Obtain and wear goggles.
2.
Obtain the laminated Reaction Matrix chart and a set of acid, base and salt solution reagents in dropping pipettes, toothpicks for mixing, litmus paper and a hand lens if available.
3.
Examine the Reaction Matrix chart. You will begin in the upper left-hand corner by placing one drop of
AlCl
3
solution so that half of the drop is on the white portion of the first reaction cell and half is on the black portion. Test the drop with a very small piece of litmus paper. Continue placing drops of AlCl
3 down the column so that half of the drop is on the white portion of each cell and the other half is on the black portion.
4.
Use the “Test Area” of the Reaction matrix to test a small drop of H
2 paper.
SO
4
with a very small piece of litmus
Adapted by Carol Brown & René McCormick from Chemtreck: Small-Scale Experiments for General Chemistry laboratory protocol by Stephen Thompson.

5.
Exercise caution as you place a drop of H
2
SO
4
solution onto the drop of AlCl
3
solution. Use a toothpick to mix the two drops together and observe any reaction taking place. Immediately record all of your observations on the Reaction Description chart and write the net ionic equation on a separate sheet of your own paper in a section titled “DATA”. If there is no visible evidence
of a reaction taking place, then record NVR in that reaction cell.
6.
Continue working down the AlCl
3
column of the Reaction Matrix chart. Be sure to write down your observations and the net ionic equations as you work your way through the matrix. Once you have completed all of the reactions on the Reaction Matrix chart, obtain a set of 5 unknown solutions from your instructor and record the letters of your unknowns in the space provided in the data section.
7.
One of your unknowns will be an acid, another will be a base. All of the unknowns are from the reagents you have been working with. You may use ONLY your 5 reagents and litmus paper to identify all 5 of your unknowns. You may mix them anyway you like on the space provided at the bottom of the Reaction
Matrix chart.
8.
Should you get “stumped” you may ask your instructor for an additional reagent but
, be prepared to present a plan. For instance, you may have identified which one of your unknowns is the acid, but be unable to determine if it is HCl or H
2
SO
4
at which time, you must formulate a plan and have it approved by your instructor who will then sign your lab sheet (or notebook) and provide you with the reagent you request for further testing. Under no circumstances are you to use an additional reagent without an instructor’s signature!
9.
Be sure to record the identity of each of your 5 unknowns matching their chemical formula to their letter as well as explain how you positively identified each unknown including any appropriate net ionic equations.
1.
Explain how to use litmus paper to determine the qualitative pH of a chemical solution.
2.
Which, if any, of the bases used in this laboratory exercise are classified as strong? Justify your answer.
3.
Which, if any, of the acids used in the laboratory exercise are classified as strong? Justify your answer.
4.
What does “strong” mean as it relates to acids or bases?
5.
Which, if any, of the salt solutions in this laboratory are colored? Justify your answer by stating why a chemical solution exhibits color.
Adapted by Carol Brown & René McCormick from Chemtreck: Small-Scale Experiments for General Chemistry laboratory protocol by Stephen Thompson.

Letter of
Unknown
Chemical
Formula of
Unknown
Evidence for Identification
(including the net ionic equation)
Adapted by Carol Brown & René McCormick from Chemtreck: Small-Scale Experiments for General Chemistry laboratory protocol by Stephen Thompson.