Read pages 27-37 - Make sure you understand graphing,
significant figures and units.
Always do INDIVIDUAL WORK (i.e. work ALONE) both in the
lab and on your reports. The only time you can work together in the
lab is if your TA gives you permission. You can discuss the lab
with each other before and after lab but when it comes time to
answer any questions it must be your own work.
ALWAYS WEAR SAFETY GLASSES - failure to do so will result in:
First offense - loss of 1/10 points (2 pts.) for that day's exp.
Second offense - loss of additional 1/10 points (2 pts.) for that day's exp.
Third offense - loss of all points (20 pts.) for that day's exp.
If you ever have to turn a lab report in late attempt to make arrangements to
give it directly to your TA. If you can not do so you can turn the report in at 100 CE.
Make sure you make a photocopy first in case something happens and your TA does not get
the report. It is YOUR responsibility to make sure your TA gets your report.
If not you will have to do the experiment again.
Corrections given below are generally for printings 1 and 2 of the 4th
edition of the lab manual, unless otherwise noted. Most of you will have printing 4 or
later, which already have the changes.
Questions: 1(a,d), 2(b,c), 4, 5b, 6 on p. 37-38
and 1, 2 on p. 45
Corrections, changes or hints to the lab manual:
Weigh a crucible, a crucible lid and the combination
(crucible + lid) using BOTH the analytical balance
and the top-loading balance. The sum of the individual
weights should equal the weight of both the crucible and
lid together (w/in experimental error of course).
Mistakes in the lab book: concerning calculating relative
deviation. First time it is mentioned in parts A and B it
is actually the relative error (assuming mass of lid and
crucible weighed together is the "true value") which is
calculated although there is no corresponding space on
the sheet. You only do the calc. for the relative
deviation as mentioned in the last sentence of Part A
and the last sentence of paragraph 2 in Part B.
The last sentence of Part A and the last sentence
of paragraph 2 in Part B should read:
"Divide the difference between each measured quantity and
the average value by the average value and multiply by
100% to obtain the relative deviation of each quantity."
Report the proper number of SIGNIFICANT FIGURES &
UNITS. Record the number of sig. figs.
where it has "Significant Place Value" on the report sheet.
Also, in Part A where it says "For each measured ...",
change the the sentence to "For each measured quantity,
indicate the number of significant figures".
The assigned questions are to be answered as part of the
Report. Your discussion should include a comparison of
the arithmetic sum vs. weighing items together; top loader
vs. analytical balance. Also, answer the questions given in
parts A & B concerning the different methods of weighing`
the objects.
Exp. 2 (Density):
Questions: 1, 3, 5, 8, 10, 12 on pp. 52-54
Corrections, changes or hints to the lab manual:
Keep the different solids in the correct bottles on the
cart.
DO NOT put a #4 rubber stopper into a 100-mL
graduated cylinder - it will not fit and can not be removed.
When using metallic samples, it is necessary to use a wide
10-mL graduated cylinder. Check the letter stamped
on the metal.
DO NOT weigh solutions in Part B by taring.
Prepare a rough graph for Part A to be checked by the TA
before leaving the lab.
Read the introductory section on graphing on pages 29-32.
Graph A - origin: 0 mL (volume), 0 g (mass) (i.e. it
should pass through the origin and the point (0,0) is
a data point. Force the line through this point while
doing a "best-fit" line to the other data points.)
Plot mass on y-axis and volume on x-axis.
Graph B - origin: 0% NaCl, 1 g/mL (density)
Plot density on y-axis and % NaCl on x-axis.
Part A - You must use 4 significantly different sizes of
the SAME material.
Return the samples to the PROPER CONTAINERS.
Exp. 3 (Specific Heat of a Metal):
Questions: 2, 3, 5 on p. 60
Corrections, changes or hints to the lab manual:
A digital temperature sensor replaces the glass and
mercury thermometer. You check these out from 231/331 CE
in exchange for your ID. You return them to the same
window when finished.
Metal piece should fit snugly into test tube. Heat metal
in boiling water for at least 15 minutes.
Record the temperature of the boiling water. This will
be the temp. of the metal. Do NOT assume the
temp. of the boiling water is 100oC.
Weigh the metal only (w/o the container).
Keep the styrofoam cup calorimeter away from the boiling
water. Record temperature immediately before adding
sample. Place the cup in a 400-mL beaker for stability
instead of the metal ring.
The law of Dulong and Petit is:
c1 * at. wt. = 1.05 x 10-23cal atom-1oC-1
Your at. wt. calculated using the above eqn. will be in g/atom. This is then converted
to amu/atom.
Show calculations for 9-11 and 13-15.
Exp. 23 (Qualitative Analysis of Cations and Anions):
Questions: 2, 3, 5, 6 on pp. 181-182
Corrections, changes or hints to the lab manual:
Do NOT put droppers into reagent bottles! You may have
one point deducted from your report grade for
this violation.
Volumes of 1 or 2 mL can be adequately measured in the micro test
tubes by comparing to a reference tube. To prepare refernece tubes
measure 1 or 2 mL of distilled water in the 10 mL graduated cylinder.
Put this in a micro test tube and mark the height with a paper label.
This system saves time and reduces the possibility of contamination with
repeated use of the graduated cylinder.
In the cation tests (Table 23A) there are several white precipitates.
It is important to describe the relative amount and the texture of the
precipitate (e.g. one is gelatinous). It may be useful to centrifuge
solutions to better view the precipitate. Try to use at least three
words to describe precipitates.
In the anion tests (Table 23B) watch for and record
evolution of a gas (i.e. bubbles) -CO2 formation: see the
equation on page 77. On page 178, the dilute
HNO3 referred to should be the 6 M HNO3 on the
cart (in plastic dropping bottles). (Check color of silver carbonate.)
Collect waste in a beaker at your bench. All waste should be collected in
large beaker and add 10 mL of 6 M NaOH. Sign the waste disposal form. Listen
to what your TA tells you to do concerning the waste.
For questions 5-7, predict reactions by comparison of reactions performed with
ions in the same group. See page 77 for reaction of carbonic acid to
form CO2.
This exp. is short. If you missed a previous exp. speak to your TA, Dr. Tatz
or Dr. Zellmer about making up a missed lab if you can.
Exp. 7 (Chemical Reactions):
Questions: 1, 2, 4-6, 7(p.84 or Table available in 100 CE) on pp. 83-84
Corrections, changes or hints to the lab manual:
You need to work in your fume hoods for this experiment.
6 M HCl is in a plastic bottle on the cart.
Test both red & blue litmus paper. Discolored litmus paper should be replaced
from 231/331 CE.
Add HCl to FeS ONLY in your hood (Part D).
Part E: iron tacks should be cleaned by immersion in 6 M HCl. Rinse the
tack with distilled water. Used tacks should be thrown in trash can.
Each student does their own experimental work. NO committees allowed.
Problem 7 (Table) will be available for students with 2nd printing
in 100 CE.
SAVE the test tubes from E-I. Have your TA check them before they
sign your data sheets.
Part I: Addition of NH3 to the CuSO4 solution may
initially cause the formation of a precipitate of Cu(OH)2. It
dissolves after all the NH3 has mixed thoroughly. You are
looking for a much deeper blue color from Cu(NH3)42+
formed after all the NH3 has mixed thoroughly with the CuSO4.
Disposal: Collect solutions from parts D, F and G in a beaker at your desk.
Transfer the waste to 1 L beaker provided and sign disposal form.
Exp. 8 (Determination of the Formula of an Oxide of Tin):
Questions: 2, 3, 4 on p. 90
Corrections, changes or hints to the lab manual:
Do NOT use 6 M or concentrated HNO3. Only 10 M is correct!
You need only 3 mL of HNO3.
A 3 inch casserole is a convenient container in which to carry a crucible and lid.
Dry containers are important for both tin and the nitric acid.
If your sample does not react with the nitric acid, it may be the wrong concentration.
You will need to start over.
Average the mass of the last two heatings in item 1 and 4 (put a line to the right
of 1 and 4). The mass of tin (item 3) should be calculated by subtracting the
average of item 1 from item 2.
Pure tin oxide would be white. Your products generally will be dark while
heating and light brown or tan when cool. The product is a mix of Sn(II) and Sn(IV)
with impurities.
Clarification of claculations between lines 8 and 9. If the calculated ratio
is not w/in 0.1 of a whole number, then factor the ratio as follows, for a ratio
of 1.858 moles O to 1.000 mole Sn.
Multiplying the 1.858:1.000 successively by 2, 3, 4, 5, 6 also does not give a
number w/in 0.1 of a whole number. When we multiply 1.858 x 7 = 13.01 the simplest
whole number ratio gives Sn7O13.
Exp. 21 (Oxidation - Reduction Reactions of the Halogens):
Questions: 1, 2, 5, 6, 7 on pp. 167-168
Corrections, changes or hints to the lab manual:
Keep the chlorine water capped TIGHTLY. The Cl2-H2O
should not be kept in open beakers at your desk. Use a STOPPERED 4-mL
test tube. Use only about 2-mL of the chlorine water (1/2 filled tube).
Do the same for the Br2 water.
Collect dichloroethane waste in a beaker at your desk and collect the silver
waste in a separate beaker at their desk. Sign the waste sheet. The
dichloroethane is flammable. During cleanup the dichloroethane goes in the
organic waste beaker in the hood and the silver goes into the metal salts beaker.
Wash test tubes thoroughly. Also, wash stoppers in-between tests. If not, you
will contaminate your solutions and the tests may give false results.
Part B: use amount of NaBr/NaI about the size of a half-grain
of rice (rather than a whole grain). This is a fairly small amount. The
reaction is performed and the colors are noted. If the color is too dark, the
aqueous layer is drawn off with a dropper and 20 more drops of dichloroethane
is added. Note the color of the dilute dichloroethane solution. Hold the test
tube up to light.
UNKNOWN:
Do bromate test first (part D). If positive you have bromate. You can stop.
Do part B test next. Use Cl2-H2O. If negative you
have NaCl. If it gives an orange color you have NaBr. If you get pink/violet
you have NaI.
Do part C test last. This will give you added confidence as to what you have.
Exp. 16 (Determination of Zinc Ion by Titration):
Questions: 1, 2, 3, 5 on p. 136
Corrections, changes or hints to the lab manual:
Read buret to 0.01 mL. Pipets deliver 5.00 mL and 10.00 mL, respectively.
Always start buret close to 0.00 mL as initial reading (i.e. refill)
Buret Reading cards are available from the storeroom.
Do not contaminate the standard EDTA solution.
For second titration and subsequent titrations, use 10 mL of Zn2+
sample only when EDTA amount is less than half of buret on the initial
titration.
5/20 of the report grade will reflect how close the reported answer is to
the "correct value".
Correct Report sheet to be Experiment 16 (if 2nd printing).
Do NOT dunk your pipet into the bottle of the standard solution or other
reagent bottles. Do NOT pour anything into the bottles. Replace
caps on the bottles. Your TA may deduct 2 points for such
"infractions".
If you use TAP WATER instead of distilled water you will experience
difficulty in attaining the end point, and your answer will be wrong.
Refer to page 18 for the definition of what is meant by a standard
solution. This should help in answering questions at the end of the report sheet.
Exp. 18 (Equilibrium):
Questions: 1-5 on p. 146
Corrections, changes or hints to the lab manual:
Each student is to do all work independently. Each student makes their own set of
solutions and determines their absorbances on the spectrophotometer. Students
share the spectrophotomoeters.
Have the TA check your absorbance before you clean up.
All concentrations have two sig. fig.. Volumes have 3 s.f. (5.00 mL) or
4 s.f. (10.00mL). K should have 2 s.f.
Exp. 20 (Acids and Bases):
Questions: 1, 2, 3, 7, 8, 10 on pp. 159-160
Corrections, changes or hints to the lab manual:
There are NO COMMITTEES OR PARTNERSHIPS - Each student works alone.
Safety glasses will be required at ALL times in the lab.
You should use standardized 0.1xxx M NaOH for the titration, NOT the 0.10 M
NaOH provided for Part A.
Part B: Use your unknown for the titration, not the vinegar provided
for part C.
Part C:
First Part: use a sodium bicarbonate solution.
Second Part: use solid sodium bicarbonate.
Read buret to 0.01 mL. The pipet delivers 10.00 mL. Check significant figures.
Buret reading cards may be obtained from the cart by the storeroom.