Lab 4 - Solubility Rules
Purpose
To develop a set of solubility rules.Goals
-
•To observe trends in solubility and exceptions to these trends.
-
•To write chemical formulas based on cation/anion charges.
-
•To learn to write net ionic equations.
Introduction
Chemical reactions can be classified into five major classes:1
Combination or Synthesis (formation) reactions:
Two substances combine to form a compound. The generic expression is:
( 1 )
A + B → C
( 2 )
2 Ca + O2 → 2 CaO
( 3 )
N2 + 3 H2 → 2 NH3
2
Decomposition reactions:
The opposite of a combination reaction, a compound breaks apart to form two or more products. The generic expression is:
( 4 )
AB → A + B
( 5 )
CaCO3 → CaO + CO2
( 6 )
2 H2O → 2 H2 + O2
3
Single Displacement Reactions:
One element, ion, or functional group displaces another element, ion, or functional group from a compound. The generic expression is:
( 7 )
A + BC → AC + B
( 8 )
Cu + 2 HNO3 → Cu(NO3)2 + H2
( 9 )
Zn + 2 HCl → ZnCl2 + H2
4
Double Displacement or Metathesis Reactions:
The atoms or ions in two or more different substances change places to form new compounds. The generic expression is:
( 10 )
AB + CD → AD + CB
( 11 )
HC2H3O2(aq) + NaOH(aq) → NaC2H3O2(aq) + H2O
( 12 )
Pb(NO3)2(aq) + 2 KI(aq) → PbI2(aq) + 2 KNO3(aq)
5
Electron Transfer or Redox reactions:
Electrons are transferred from one substance to another. These will be treated separately in this lab course.
( 13 )
F = k ·
q1q2 |
εr2 |
( 14 )
Pb2+(aq) + 2 NO3−(aq) + 2 K+(aq) + 2 I−(aq) → PbI2(s) + 2 K+(aq) + 2 NO3−(aq)
( 15 )
Pb2+(aq) + 2 I−(aq) → PbI2(s)
Equipment
Reagents
Anions (rows)
Cations (columns)
Safety
Some of the cation solutions are toxic. Do not ingest them. If you spill any on yourself, wash well with soap and water. Avoid putting anything in your mouth while in lab, ex. chewing on fingernails, pens and pencils. Silver solution will form dark spots on skin if spilled. The spots will not appear for about 24 hours, as the ions are slowly reduced to the metal. They are not hazardous, and will fade in a few days.Waste Disposal
All of the solutions prepared in this experiment should be discarded in the waste container on the side shelf. You may wish to have a beaker in your work area to collect waste while you are doing the experiment. Make sure it is labeled. Use a squeeze bottle of deionized water to rinse the solutions into the beaker; use the minimum amount of water you can, to avoid creating large volumes of waste solution. The plates and test tubes can then be washed in the normal manner.Lab Procedure
Please print the worksheet for this lab. You will need this sheet to record your data.Part A: Investigating Trends in Solubility
1
Obtain an 8 × 12 plastic well plate. You will be mixing ions in the well plate. The combinations of ions are listed in the grid in Table A.
2
In order to keep track of what you are doing, put your solutions into the well plate in the same order they are listed in Table A.
3
Add three drops of each solution listed to the well. (More is not better!) Be careful to drop the solution into the well without touching the grid or any solution that is already in the well. If the dropper touches another solution, the reagent in the dropper bottle will become contaminated. Place your cations (nitrate solutions) in columns. Place your anions (sodium solutions) in rows.
4
Record your observations in Table A. If a precipitate forms, put a Y in the space that corresponds to the two solutions that were mixed. If no reaction occurs (no precipitate forms), put an N in the appropriate space in the table. If you cannot see a result clearly in the well plate, repeat the experiment in a small clean test tube.
5
Make note of any observations other than precipitation below the table. For example, if a precipitate is colored or appears gelatinous, a comment to that effect should appear on your worksheet.
Part B: Investigating Some Exceptions to the Solubility Rules
1
In two of the unused wells of your well plate, mix the solutions listed in Table B, as you did for Part A.
2
Record your observations in Table B. If a precipitate forms, put Y in the space that corresponds to the two solutions that were mixed. If no reaction occurs (no precipitate forms), put an N in the appropriate space in the table. If you cannot see a result clearly in the well plate, repeat the experiment in a small clean test tube.
3
When you are finished, collect all your waste and deposit it in the waste container provided on the side shelf. Use a minimum amount of water to rinse residual solutions into the waste container. Then clean and dry all your equipment and return it to the set-up area where you found it.
4
Before leaving, go to a computer in the laboratory and enter your results in the In-Lab assignment. If all results are scored as correct, log out. If not all results are correct, try to find the error or consult with your lab instructor. When all results are correct, note them and log out of WebAssign. The In-Lab assignment must be completed by the end of the lab period. If additional time is required, please consult with your lab instructor.