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Exercise 5:
Chemical Properties
Introduction
In the experiment two weeks ago you identified unknown substances based upon their
physical properties. In this weeks experiment you will identify three unknown solutions on the
basis of their chemical properties, that is, whether or not they undergo chemical reactions when
mixed with another chemical. Your three unknown solutions will be from the following list:
AgNO3, Cu(NO3)2, HCl, Fe(NO3)3, Na2SO4, Na2CO3, and NaOH. In the first part of the
experiment, you will determine what chemical reactions are possible between these various
solutions. After observing and recording your data for the first part of the experiment, you will
use this set of reference reactions in the second part of the experiment to identify your unknown
solutions.
Procedures
Part A. Construction of Reference Reaction Grid
1. Clean and dry 6 test tubes.
2. On the top of each lab bench, you will find sets of 7 chemical reagents. Place five drops of
any one reagent into all 6 test tubes.
3. Into the first of the 6 test tubes, place 5 drops of a reagent not used in step 2. Into the second
of the 6 test tubes place five drops of another reagent not used in step 2. Repeat this process
until you have used all of the reagents that were not used in step 2.
4. Observe and record whether a chemical reaction occurs. For these reactions, you will be
looking to see if a solid (precipitate) forms. The precipitate should sink to the bottom of the
test tube. In addition, observe and record the color of the solid (precipitate). It is extremely
important that you record the observations in the correct block of Data Table A.
5. Dispose of the solutions/precipitates from step 3.
6. Clean and dry 6 test tubes.
7. Place five drops of a reagent other than the one previously used in step 2 into all 6 test tubes.
8. Into the first of the 6 test tubes, place 5 drops of a reagent not used in step 7. Into the second
of the 6 test tubes place five drops of another reagent not used in step 7. Repeat this process
until you have used all of the reagents that were not used in step 7.
9. Observe and record in Data Table A whether a precipitate formed, and if so, its color.
10. Repeat steps 5 through 9 until you have completed all the possible combinations of two
reagents.
11. You can essentially cut your work in half if you think carefully about the reactions you are
performing. Look at Data Table A and think about duplicate reactions that can be skipped.
If you are not sure, ask your instructor.
12. Even if you used the shortcut to save time, completely fill in Data Table A, as it will simplify
your task in Part B.
Part B. Identification of Unknown Solutions
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1.
2.
3.
4.
5.
Obtain your three unknown solutions from your instructor.
Record your unknown numbers in Data Table B.
Clean and dry 7 test tubes.
Place five drops of one of your unknown solutions into all 7 test tubes.
Into the first of the 7 test tubes, place 5 drops of one of the known reagents. Into the
second of the 7 test tubes place five drops of another known reagent. Repeat this process
until you have used all of the known reagents.
6. Observe and record whether a chemical reaction occurs. In addition, observe and record
the color of the solid (precipitate). It is extremely important that you record the
observations in the correct block of Data Table B.
7. Dispose of the solutions/precipitates from step 5.
8. Clean and dry 7 test tubes.
9. Place five drops of a different unknown solution into all 7 test tubes.
10. Into the first of the 7 test tubes, place 5 drops of one of the known reagents. Into the
second of the 7 test tubes place five drops of another known reagent. Repeat this process
until you have used all of the known reagents.
11. Observe and record whether a chemical reaction occurs. In addition, observe and record
the color of the solid (precipitate).
12. Repeat steps 6 through 10 with your final unknown solution.
13. Dispose of all solutions/precipitates.
14. Compare your results from Part B to Part A. You should be able to identify your
unknown solutions by comparing which mixtures produced precipitates and their colors.
15. Record the identity of your unknown solutions.
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Data Sheet for Exercise 5:
Chemical Properties
Data Table A. Reference Grid
Substance
AgNO3
AgNO3
xxxxxxx
xxxxxxx
Cu(NO3)2
Cu(NO3)2
Fe(NO3)3
Na2SO4
Na2CO3
HCl
NaOH
xxxxxxx
xxxxxxx
Fe(NO3)3
xxxxxxx
xxxxxxx
Na2SO4
xxxxxxx
xxxxxxx
Na2CO3
xxxxxxx
xxxxxxx
HCl
xxxxxxx
xxxxxxx
NaOH
xxxxxxx
xxxxxxx
Data Table B. Unknown Identification
Substance
AgNO3
Cu(NO3)2
Unknown
___
Unknown
___
Unknown
___
Unknown ___ is __________.
Unknown ___ is __________.
Unknown ___ is __________.
Fe(NO3)2
Na2SO4
Na2CO3
HCl
NaOH
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Exercise 5:
Chemical Properties, Pre-Lab Questions
1. A student performing a similar experiment found the following results after mixing her
known solutions together:
a) H2SO4 + Pb(NO3)2  white solid
b) Zn(NO3)2 + NH3  white solid
c) Zn(NO3)2 + Na2S  white solid
d) Pb(NO3)2 + NH3  white solid
e) Na2S + Pb(NO3)2  black solid
Completely fill in the table below:
Substance
H2SO4
H2SO4
xxxxxxxxxx
xxxxxxxxxx
Na2S
Na2S
NH3
Pb(NO3)2
Zn(NO3)2
xxxxxxxxxx
xxxxxxxxxx
NH3
xxxxxxxxxx
xxxxxxxxxx
Pb(NO3)2
xxxxxxxxxx
xxxxxxxxxx
Zn(NO3)2
xxxxxxxxxx
xxxxxxxxxx
2. The student found the following results for her two unknown solutions:
a) Unknown 1 + Na2S  white solid
b) Unknown 2 + Pb(NO3)2  white solid
c) Unknown 1 + NH3  white solid
Completely fill in the table below:
Substance
H2SO4
Na2S
Unknown 1
Unknown 2
3. On the basis of the data in questions 1 and 2:
NH3
Pb(NO3)2
Zn(NO3)2
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Unknown 1 is __________.
Unknown 2 is __________.