Name: ___________________________________________________ Hr: __________ DUE Date: ____________
Unit 8 Chemical Reactions Lab: The 12 Solution Problem
Objectives:
 Examine the results of combining aqueous solutions in potential double replacement reactions
 Verify if a double replacement reaction has occurred
 For reactions that did occur, translate into complete and net ionic equations while identifying spectator ions
 Used recorded observations to identify 2 unknown solutions
Introduction:
Part 1: Observing chemical reactions and writing net ionic equations: A substance made only of a single type of
molecule in its liquid phase at room temperature, is simply called a “liquid”. For example, water is composed only of H 2O
molecules, and, therefore, is called a liquid. One can make a solution by uniformly combining two different substances so
that the mixture is homogeneous. An aqueous solution is composed of a liquid solvent (water) and a solute which solid at
room temperature but dissociates (breaks apart into ions) when mixed with water. This solute is an ionic compound or an
acid. For example NaCl(aq), or salt water, is composed of mostly H2O molecules and several Na +1 and Cl -1 ions. The
solution is homogeneous, meaning you cannot distinguish between the water molecules and the solute, but it is NOT liquid
since it is composed of a) more than one type of molecule and b) the solute is the type of particle that dissociates when in
water.
Up until now, you have only been required to write the molecular equation. We are not going to work toward writing
complete ionic equations and net ionic equations. Because ionic compounds and acids dissociate in water, it is more
accurate to represent NaCl(aq) as Na +1 (aq) + Cl -1 (aq) when writing a chemical equation. All aqueous solutions can be
written in this format. Non-aqueous substances-solids, liquids, and gases—do not dissociate in water and, therefore, should
remain united as a compound in the chemical equation. For example, if aqueous sodium chloride reacted with aqueous
barium nitrate to produce aqueous sodium nitrate and solid barium chloride, the unbalanced complete ionic equation
would look like:
Equation 1:
Na +1 (aq) + Cl -1 (aq) + Ba +2 (aq) + NO3 -1 (aq)  Na +1 (aq) + NO3 -1 (aq) + BaCl2(s)
Notice we have two chlorides on the product side, so we should really add a coefficient of 2 in front of the chloride ion on the
reactant side.
A net ionic equation consists only of the solid, liquid, or gas produced on the product side and the ions that were used to
produce this product on the reactant side:
Equation 2:
Ba +2 (aq) + Cl -1 (aq)  BaCl2(s)
The ions in the complete ionic equation (equation 1) that did not produce the non-aqueous product are called spectator ions
(they didn’t actually participate in making product—they simply “watched”).
Part 2: Identifying an unknown: The art of logical thinking is essential to mastering chemistry. Although it is important to
be familiar with many chemical facts so that you can utilize the language of chemistry effectively, it is even more important
to be able to assimilate these facts and organize them in logical ways so they can be used to solve problems. You are going
to use part 1 to observe 8 solutions interactions with one another. In part 2, you will be assigned 2 unknowns (2 unknowns
per student). Each unknown is one of the tested solutions. You will need to identify each unknown and justify with your
data.
p. 1
Name: ___________________________________________________ Hr: __________ DUE Date: ____________
Pre-Lab Questions:
1. As you know, there are 4 observable signs that a chemical reaction has taken place—precipitate, gas (look for
bubbles when using solutions), change in energy (light or heat), or color change. In the lab, you will be looking for
all of these except change in energy. What would you look for in a written double replacement reaction to
determine if the reaction actually occurred (hint: consider the phase symbols)?
2. Complete the following double replacement reactions by writing the products, phase symbols and balancing. Write
“N.R.” for “no reaction” if the reaction does not occur. Note: carbonic acid, H2CO3 immediately breaks down to water
and carbon dioxide gas, so you can just write those products in place of H2CO3.
a. ____NaCl(aq) +
_____AgNO3(aq)

b. ____NaI (aq)
+
_____HNO3(aq)

c. ____Na2CO3(aq)+
_____HNO3(aq)

3. In the question above, you wrote the “molecular equations” for three reactions. Using same three reactions, write
the complete ionic equation and then the net ionic equation. You should include phase symbols (aq after any ion),
charges on the ions, and remember to keep non-aqueous substances as a compound. Ignore the coefficients for
now.
a. ____NaCl(aq) +
_____AgNO3(aq) 
i. Complete:
ii. Net:
b. ____NaI (aq)
+
_____HNO3(aq)

_____HNO3(aq)

i. Complete:
ii. Net:
c. ____Na2CO3(aq)+
i. Complete:
ii. Net:
4. In the reactions for #3, use coefficients to balance the number of each element on the product and reactant side.
5. In the reactions for #3, circle the spectator ions.
p. 2
Name: ___________________________________________________ Hr: __________ Date: ____________
Materials per group:
 2 well plates (or spot plates)
 Q-tips to clean wells
 Toothpicks or stirring rod
 Known solutions: see data table
 White paper—to add labels & look for precipitate
Safety:
*Nitric acid (HNO3) is extremely corrosive to skin. Immediately stopper the solution once it has been used. Silver nitrate
can cause skin to stain black. Lead nitrate and silver nitrate are toxic. You will not know which solution is your unknown so
assume EVERYTHING is corrosive and toxic.
Procedure:
PART 1
1. Inspect your well plates. They have been cleaned, but if the wells appear cloudy, wipe with a Q-tip. Save the Qtips for further cleaning.
2. The labels on your Data Table show the solutions to be mixed in each well. For example, in the top left well you are
mixing nitric acid and silver nitrate. To avoid wasting time and materials, do not mix a substance with itself and do
not mix the same two substances more than once. Place Xs or shade in the squares of your labeled Data Table to
show where you do not need to mix solutions.
3. Place both well plates on the provided white piece of paper and label which solutions are going into each well on
the paper. This is a very important step which may save you a lot of frustration.
4. You will be using only 3 drops of each solution for one mixture. For example, in the top left well you will add 3
drops of nitric acid and 3 drops of silver nitrate, for a total of 6 drops in the well. Stir with a toothpick or a rinsed
stirring rod for at least 20 seconds (remember to rinse the rod to avoid contamination).
NOTE: Be aware of time constraints. These materials will be used by the following hour so your work cannot be saved. I
suggest completing a row or a column, take observations, then check the time to determine if you can do another.
5. It is very important you make excellent, detailed observations on your data table.
a. If a reaction occurs, note with a “+” sign. If a reaction does occur, provide further detail. Was a gas
produced b/c you saw bubbles? Was there a color change? If so, what to what color? Was a solid formed?
If so, what color is the solid? Does the mixture appear to be a solution, colloid, or suspension? Use the
letters on the white paper to help with the determination.
b. If no visible reaction occurs, note with the abbreviation “NVR”. Underneath include a general description of
the mixture—color, clarity, etc…
6. Dispose of the mixtures by rinsing the well plates with water, wiping each well with a Q-tip or paper towel, and
tapping the well plates dry.
PART 2
7. Each individual will be assigned unknowns. Each unknown is one of the 8 solutions, but you will have to test to
determine which solution. Obviously your observations and testing methods must be meticulous.
a. Record your observations for your unkowns in the provided Unknown Data Tables, as well as your
prediction as to what you believe your unknown to be.
b. Also on your Uknown Data Tables, provide written clarification as to why you believe your unknown to be a
particular solution base on how the unknown reacted (or didn’t react) with the test solutions. For example,
“I believe unknown Z is hydrochloric acid because it reacted with nitric acid to produce a white solid,
reacted with silver nitrate to produce a black solution, and did not react with the other substances.”
c. Bring remaining unknown back to Ms. V, rinse well plates, and wipe with a Qtip.
p. 3
Name: ___________________________________________________ Hr: __________ Date: ____________
NOTE: while you will be collecting part 1 data with a team, the bulk of the lab is individual. You will complete your
own pre-lab questions, part 1 data table, post lab questions, and you will have to identify two unknowns
Post Lab Questions:
1. Write and balance chemical equations for each precipitation reaction you observed for lead (II) nitrate. HINT: use
“NH4OH” for NH3 b/c when ammonia is in water it forms ammonium hydroxide. (should be 9 equations).
2. Which reactions gave distinctive bubbles? What chemicals do al these reactions have in common? Write chemical
equations to describe all the reactions that produced bubbles (should be 3).
3. Write net ionic equations for all of the sodium carbonate reactions that gave evidence of reaction (should be 8).
p. 4
Name: ___________________________________________________ Hr: __________ Date: ____________
4. Which reactions gave color changes but no precipitate?
5. Which mixings could you have predicted in advance would not result in a reaction?
6. Investigate further the reaction of copper (II) sulfate with ammonia (NH3). Try 1 drop of ammonia with 5 drops of
copper (II) sulfate. Then try 1 drop of copper (II) sulfate with 5 drops of ammonia. Compare the two reactions.
7. A very distinctive precipitate is formed when sulfuric acid and calcium chloride are mixed. How does this precipitate
differ from the other precipitates observed in this lab? (repeat back in the lab if needed).
8. Imagine a student was performing this same lab, but committed the following errors. Describe how (and why) each
error would affect the data (the observations):
a. After stirring the Pb(NO3)2 / AgNO3 well with a glass stirring rod, the student forgot to rinse the stirring rod
before mixing the HCl / NH3 well.
b. When the blue CuSO4 solution was combined with the colorless HCl, the student recorded the light blue
substance as having a color change.
c. A student mixed H2SO4 and calcium chloride, but did not stir. After waiting only 10 seconds, the student
wrote NVR.
p. 5