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Date:
Lab: Mystery Solutions Precipitate Lab; Double Replacement Reactions
BACKGROUND
Precipitation reactions occur when two chemicals react to form a product that is insoluble in water and falls out
of solution. A precipitate is a solid substance that separates from solution during a chemical reaction. A
precipitate can be identified by the cloudy, milky, gelatinous, or grainy appearance it gives to the mixture.
In this lab, you will observe multiple precipitation reactions using mixtures of known and unknown solutions.
By using the data and the solubility rules, you will be able to determine the identity of the unknown solutions.
MATERIALS AND EQUIPMENT
Known Solutions: HCl, AgNO3, K2CrO4, Na2CO3
Unknown Solutions: HCl, AgNO3, K2CrO4, Na2CO3, Pb(NO3)2, NaNO3
Reaction Sheet
SAFETY
Safety goggles must be worn at all times. Many of the solutions can cause skin damage.
PROCEDURE
1. Record your observations of each known solution and unknown solution in the data table below.
2. Using the reaction sheet as your guide, add 2 drops of HCl to the first square. Add two drops of
Unknown Solution 1 to the same square.
3. Observe and record any reaction or lack of reaction.
4. Continue this process with each Known-Unknown combination.
5. If possible, take a picture of your reaction sheet.
6. Gently rinse reaction sheet and wipe clean.
DATA
1
HCl
AgNO3
K2CrO4
Na2CO3
2
3
4
5
6
DATA ANALYSIS
1. Predict the products and balance the equations for each combination of Known and Unknown solutions.
Be sure to include phases. If there is no precipitate, you may write: No Reaction. If there is a
precipitate, write the net ionic equation.
A.
HCl(aq)
+
AgNO3(aq) 
+
K2CrO4(aq) 
+
Na2CO3(aq) 
+
Pb(NO3)2 (aq) 
+
NaNO3 (aq) 
+
K2CrO4(aq) 
+
Na2CO3(aq) 
+
Pb(NO3)2(aq) 
Net Ionic:
B.
HCl(aq)
Net Ionic:
C.
HCl(aq)
Net Ionic:
D.
HCl(aq)
Net Ionic:
E.
HCl(aq)
Net Ionic:
F.
AgNO3(aq)
Net Ionic:
G.
AgNO3(aq)
Net Ionic:
H.
AgNO3(aq)
Net Ionic:
I.
AgNO3(aq)
+
NaNO3(aq) 
Net Ionic:
J.
K2CrO4(aq)
Net Ionic:
+
Na2CO3(aq) 
K.
K2CrO4(aq)
+
Pb(NO3)2(aq) 
+
NaNO3(aq) 
+
Pb(NO3)2(aq) 
+
NaNO3(aq) 
Net Ionic:
L.
K2CrO4(aq)
Net Ionic:
M.
Na2CO3(aq)
Net Ionic:
N.
Na2CO3(aq)
Net Ionic:
2. Consider the following descriptions of the precipitates/ products of the reactions. Based upon the
descriptions below, your data, and your written equations, determine the identity of the unknown
solutions.
AgCl—white solid
Ag2CrO4—brown-red solid
Ag2CO3—pale yellow
H2CO3—clear, bubbles
PbCl2—white solid
PbCrO4—bright yellow solid
PbCO3—white solid
Identities of Unknowns
Unknown 1:
Unknown 2:
Unknown 3:
Unknown 4:
Unknown 5:
Unknown 6: