CHE112 Laboratory
Overview
We will be doing assignments 2 through 6 from the text, “A Manual for General Chemistry
Laboratory II”, By James C. Horvath. This must be purchased at the College Store on PSU
Campus before lab classes begin—take it to the first day of lab. Read the prelab for Assignment
2 before you go to the first lab on the first day of lab. This lab is self-paced. Read the prelab for
each assignment before you begin the assignment. If you prepare for each experiment by reading
ahead and understanding the material and what you will be doing before you come into the lab,
you should have no problem completing all of the assignments and unknowns. The point
breakdown of the assignments is:
Assignment
2
Unknown 2
3
Unknown 3
4
5
Unknown 5
6
Unknown 6
Total
Total Points:
Exercises
125
150
100
170
100
N/A
200
125
230
1200
1450
Problems
50
N/A
50
N/A
50
50
N/A
50
N/A
250
Time (hrs)
6
1.75 (1 hour 45 min. time limit)
4.5
2.00 (2 hour time limit)
4
N/A
2.25 (2 hour 15 min. time limit)
5.5
2.50 (2 hour 30 min. time limit)
28.5
Lab Overview:
The ideal behind this lab is that students work through the material learning qualitative methods
for determining the presence of certain ions, such as HSO4– or K+. After students complete the
first experiment, Assignment 2, they should prepare to do an unknown. If there is any time left
during the laboratory day to work on Assignment 3, they should do so. The next lab day, the
student will be given an unknown, Unknown 2, to analyze for the ions studied in assignment 2.
There will actually be two packets, one for Unknown 2A and the other for Unknown 2B.
Unknown 2A is guaranteed to be a pure salt. Unknown 2B can be a mixture of 1 to 3 salts.
After completing the unknown, the student will continue work with Assignment 3. When the
student completes assignment 3, the unknown process starts again with Unknown 3 (A (a pure
salt) and B (a mixture of 1 to 3 salts)). When the student has completed Assignment 4, he or she
will need to complete assignment 5 at home (it’s a “paper lab”). The student will then get
another unknown compound, Unknown 5A and 5B. As with Unknowns 2 and 3, Unknown 5A is
guaranteed to be a pure salt while Unknown 5B can be a mixture of 1 to 3 salts. Following
assignment 6, unknown 6 should be done. Again, unknown 6A is guaranteed to be a pure salt
while unknown 6B can be a mixture of 1 to 3 salts. Each student will get 105 minutes for
unknown 2, 120 minutes for unknown 3, 135 minutes for unknown 5 and 150 minutes for
unknown 6. Students may use their lab books, assignments and anything else they want to use
(as long as it is generated by that student) to help them during their unknown analysis (except the
help of other people!) The point is for students to become problem solvers, not to memorize
testing techniques.
This lab is self-paced. Students may work on each lab assignment as long as they like.
However, I must caution you that you should be motivated to use your lab time wisely. If a
student does not make good progress, that student will not complete all of the assignments and
unknowns by the end of semester. This will be reflected in the student’s grade! Reading the prelab material and learning the names of compounds and how to dilute solutions will be very
helpful in using the lab time wisely. These three things alone will make student progress through
the lab assignments significantly greater.
Because of the self-paced nature of this lab, many of the Assignments take more than 1 lab
session. Some of the students may complete Assignment 2 in the middle of the 2nd scheduled lab
session (week 3) while some will need all or most of the 2nd lab session to complete it. Students
should not do unknown 2 during the 2nd lab session unless they completed Assignment 2 on the
first day. If students complete Assignment 2 during the second day and have more time left in
the lab period, they should begin work on Assignment 3. The next week they should do
Unknown 2 in the beginning, and then continue (or begin) working on Assignment 3.
For each unknown, the student should produce a scheme of analysis. The schemes are often the
last problem in the problem section of the assignments and will not be graded. For example, the
scheme for Unknown 2 is the answer to P2.11 on page 2-23 and will not be graded. You are in
charge of doing the unknown and making sure that you use good, sound judgments while testing
your unknown. A good scheme will help in this matter!
Due Dates: Each lab assignment is to be turned in the week following its completion. If there is
an unknown associated with the assignment, the assignment should be turned in after the
unknown is completed. The student will need all of the assignments completed in order to do the
unknown and in order to prepare their scheme of analysis at home the week before the unknown.
Unknown 6 should be done before or on the last day of lab work, during the week of May 5th.
Other tips and useful information:
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Students should never bring reagent bottles to their work area. The reagent bottles are to
remain in the reagent bottle storage area.
I don't think students will ever need more than a few drops or a mL of a solution. Thus, it
is unreasonable for students to walk up to a reagent bottle with beaker in hand to collect
the reagent.
Students may use their lab assignments when doing unknowns.
Most of the chemical equations that need to be written during lab are written in the prelab write up. Most of the theories used are also explained in the prelab.
Reading the prelab will help each student be more capable of answering the questions in
the lab. Students should read the pre-lab material before they come to class.
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When doing problems at the end of the lab assignments, use the prelab and your answers
to questions within the lab to help determine the answers.
There is a very useful acid/base table that also gives good information about solubility on
the front cover of the lab manual.
Each assignment is due the next lab day after the date the assignment is completed.
Unknown 2 should be done the lab day after Assignment 2 is completed.
Much of the information that you write during lab will be helpful when you do your
unknowns—make sure your written descriptions and answers to the questions in the
experimental section are good, thorough and correct.
There are Instructor OK checkpoints every page or two. Students are not allowed to
move beyond each of these points until they receive the instructor’s initials at each of
these “OK” checkpoints.
Before getting an initial at the OK points, make sure that your answers to the questions
are correct. The prelab can be very helpful in this matter!
Always use DI water for all of your experiments!
The dilution of solutions do not have to be exact—only approximate and many of the
experiments call for small amounts of solution. Since 1 drop is about 0.03 to 0.05 mL
(20-30 drops per mL), drops can be used instead of mL when making dilutions. For
example, an approximately 0.01 molar NaCl solution can be prepared by adding 1 drop of
1 M NaCl to 3 mL of water (since there are approximately 20-30 drops per mL).
When the text asks for a chemical reaction, only the net ionic reactions are needed and
only the net ion reaction is correct. Most students are fairly insecure about this at first—
but after some time students become more comfortable with this idea.
Equilibrium reactions (like the equilibrium that exists in a solution with a little AgCl in
the bottom) require equilibrium arrows while one-way reactions (like the principal
reaction that occurs when AgNO3 solution is added to NaCl solution) require one-way
arrows. The text often hints at this when asking for the reaction, like “Write the
equilibrium reaction which accounts for...” (two-way arrow) or “Write the principle
reaction which occurred when ...” (one-way arrow).
Only H3O+ will be accepted for the representation of the principle proton-containing
species in a strong acid, H+ will not be accepted since this suggests it is not attached to
anything.
Students will need to use hoods at times. They will assemble a snorkel-type hood. These
hoods get very hot! Only use them when you need them. This will be for part 4 of
Assignment 2.
Solutions and compounds:
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Many of the experiments will call for a certain molarity of a solution. The solutions
available are not always of the same molar concentration needed. Students will need to
dilute more concentrated solutions to get the desired concentrations.
Many of the experiments call for a solution containing some ion, such as K+ or
Mg(H2O)62+. There are reagents with these ions, such as KCl or MgCl2. Students need to
learn in lab that these solutions can be used and that the higher charged and smaller
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metals such as Mg2+ exist in the hydrated form (like Mg(H2O)62+ ), with usually with 6
waters.
Some of the experiments do not specify a concentration. In these cases it is usually best
to use a 0.1 M solution.
The acids and bases are in the hoods.
There are two setups of bottles of reagents for the experiments, one entire setup on each
side of the hoods.
Tips for Assignment 2:
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Assignment 2 takes 1 to 2 lab sessions.
Make sure you make good written descriptions of experimental observations and
techniques.
The main gist of the experiment is all about detecting the presence of ions in a solid
sample that each student will receive at the end of the lab. Students will perform some
tests directly on the solid (flame test and the test for NH4+ described in Q2.16) and some
tests on a solution the student makes from their unknown solid. The solution made will
be approximately 0.05 to 0.15 molar in the unknown ions. Thus, when testing solutions
in the experimental portions of each assignment, students will probably want to make
solutions that are 0.1 M.
“Fair game” ions (ions that will be in the unknown) are listed on page 2-3.
In the lab manual, HSO4– is shown as HOSO3– and HNO3 is shown as HONO2. Students
should get used to writing HSO4– and HNO3 while reading HOSO3– and HNO3.
Hydroxide, OH–, is written in the lab manual as HO– in an effort to show where most of
the charge lies (on the oxygen). Please write it as OH–.
In section 1, nitric acid does not really clean the nichrome wire well. To clean the
nichrome wire, just hold the tip of the wire in the hot spot of the flame (about an eighth of
an inch above the bright blue cone of the flame) until the tip of the wire no longer has a
yellow flame coming off.
To get the pH of any solution in this lab, use the pHydrion paper. Having a couple of
significant figures beyond the decimal is really not important nor desired since the
concentration of dissolved unknowns will not be known exactly.
When testing a solution to see if it is basic or acidic, use litmus paper, not pHydrion
paper.
When litmus paper is needed, neutral litmus paper can be used instead of red or blue
litmus paper. Neutral litmus turns blue in basic solution and red in acidic solution.
Any solutions containing Ag+ or Ag+--containing precipitate (ppt) should be put in the
silver waste container, any solutions containing the cobaltinitrite or ppt’s or cobaltinitrite
should be put in the cobaltinitrite waste container and any solutions containing Ba2+ or
Ba2+--containing ppt should be put in the barium waste container.
There really is no leeway in the chemical equations that need to be written—they are
either correct or not correct. Many of them are in the pre-lab material!
Have fun!