Chemistry 153
Clark College
SYNTHESIS AND ANALYSIS OF A COORDINATION
COMPOUND OF COPPER
A capstone experiment – Adapted from Jack Kotz, SUNY-Oneonta
For this experiment:

Complete the pre-lab and obtain a stamp before you begin the actual experiment.

Write out your lab notebook pre-lab – you already have the synthesis section, now add the 3
analyses sections (precipitation, titration, and colorimetry).

Determine the formula of your coordination compound.

Make your OWN results table(s) to attach to the lab.
For this lab, you will only need to turn in the following: a results table that you create including
sample calculations, your calibration plot from Cu+2 analysis, your lab notebook pages, and the
stamped pre-lab.
PROCEDURE
Part 2: Analysis for Sulfate Ion, SO421. Weigh to the nearest 0.1 mg about 1 gram of your compound (after making absolutely sure it is
dry). Record the actual mass of sample used.
2. Dissolve the solid compound in 10 mL of 6 M nitric acid (HNO3). The reaction occurring at this
point is:
Cux(NH3)y(SO4)z +· a H2O + y H+1  x Cu2+ + y NH4+1 + z SO42- + a H2O
During addition of nitric acid to the unknown compound, the originally deep violet
solution will turn light blue.
3. Obtain ~5 grams of calcium nitrate [Ca(NO3)2], and add it to the solution until precipitation is
complete. The calcium nitrate is soluble thus it will form Ca+2 and NO3-1 ions in solution. The
reaction now occurring is:
Ca2+(aq) + SO42-(aq)  CaSO4 (s) (white in color)
Use the following procedure to isolate the precipitate: Obtain a glass fritted crucible.
LABEL it in permanent marker with your name and trial number (you will be
performing two trials!) and weigh it on the analytical balance – record the mass of the
fritted crucible in your notebook. Once it has been weighed, do NOT touch it with your
bare hands – use gloved hands or tongs only. CLEAN and set up the vacuum
apparatus (very similar to vacuum filtration used previously). Filter the precipitate.
Be sure to disconnect the hoses in the correct order or you may literally blow your
glass crucible off the erlenmeyer flask! Check the filtrate by adding approximately 0.5
grams more of Ca(NO3)2. If more ppt forms, refilter. If no ppt forms, you have
precipitated out all of the sulfate. After you have checked the filtrate and re-filtered (if
necessary), and your sample is WHITE, NOT BLUE, you can do a final rinse of your
precipitate on the fritted crucible with acetone. The filtrate may go down the drain.
The glass fritted crucible will go into the oven to dry. Place both crucibles in a beaker
(so they stay upright) and put in the oven.
Note***: Acetone, H3CCOCH3, forms hydrogen bonds with water. This assists in removing water from the precipitate and thereby hastening its
drying.
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Chemistry 153
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4. After the sample has dried, it will be removed from the oven and placed in a dessicator (prevents
moisture from getting in your sample) to cool for 20 minutes. After the fritted crucibles are cool,
reweigh to obtain the amount of CaSO4 obtained for each trial.
5. Once the final mass of CaSO4 is determined, please dispose of the solid waste in the appropriate
container. The fritted crucibles can be cleaned like any other piece of glassware.
6. As mentioned above, a total of TWO determinations of the amount of sulfate must be carried out.
Part 3: Volumetric Analysis for Ammonia, NH3
The amount of ammonia in your compound will be determined by a conventional acid-base titration.
That is, using the reaction:
y NH3(aq) + y H+1(aq) → y NH4+1(aq)
where H+ is from a standardized solution of strong acid, that is, from HCl.
1. Weigh out, to the nearest 0.1 mg, two 1 gram samples of your compound, and dissolve each in
about 30 mL of water. (Note: as you do not want to allow the solutions to stand very long before
titrating them, you should weigh out the samples one at a time and use the solution immediately)
2. Add 10 drops of methyl orange indicator to each solution, and titrate each with thorough stirring
with standard HCl. (The acid concentration is approximately 0.5 M; the exact concentration will be
given to you.)
Numerous color changes occur as acid is added. The solution starts out deep blue. However, as acid is
added the color changes to a blue-green and then to a pea-green when about 70% of the acid has been
added. After about 85% of the ammonia has been titrated, the color is distinctly yellow. The end point
is a change from yellow-orange to red-orange. However, the end point detection is made even easier by
the fact that the precipitate that was present through the titration vanishes just before the end point. Be
sure to comment on the changes that the solution undergoes in your lab notebook.
Note***: closest example to endpoint color
cloudy
And the sample will be CLEAR – not
3. Record your results and observations for each titration. Again, a total of TWO titrations must be
done.
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Chemistry 153
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Part 4: Spectrophotometric Analysis for Copper ion, Cu2+
1. Clean and dry seven test tubes, and label them 1 through 7 using tape and indelible ink. Set them
aside. You will fill them later (step 3!). The first four of these tubes will be used to make up the
reference solutions that are then used to generate your calibration curve using the Vernier data
acquisition system and LoggerPro.
2. Prepare calibration standards and samples of the unknown compound according to the directions
in the Table below. Calculate the concentration of the copper ion in each solution using the
equation C1V1 = C2V2. You will need these values when you use LoggerPro.
3. You will be using volumetric glassware to make these solutions. Solutions will either be prepared
using 10.00 mL volumetric flasks and/or graduated glass pipets. Solutions should NOT be
prepared using plastic pipets, graduated cylinders, or beakers. Once the solutions are made, you
can transfer them to the clean, dry labeled test tubes you prepared in step 1.
TABLE Preparing Calibration Standards and Samples of Unknown for
Spectrophotometric Analysis
Test tube
Contents
ID
1
2
3
4
5
6
7
Solvent only – HNO3 to calibrate the colorimeter
4.0 mL of copper (II) solution and 6 mL of standardized 1 M
HNO3 solution (use graduated pipets here)
7.0 mL of copper (II) solution and 3.0 mL of standardized 1 M
HNO3 solution (use graduated pipets here)
10.0 mL of copper (II) solution (use a graduated pipet to
measure this solution)
Weigh, to the nearest 0.1 mg, 0.2 grams of solid unknown and
dissolve in 10.0 mL of 1 M HNO3 (use 10.00 mL vol flask)
Weigh, to the nearest 0.1 mg, 0.25 grams of solid unknown
and dissolve in 10.00 mL of 1 M HNO3 (use vol flask)
Weigh, to the nearest 0.1 mg, 0.3 grams of solid unknown and
dissolve in 10.00 mL of 1 M HNO3 (use vol flask)
4. Open “Experiment 11 Beer’s Law” using LoggerPro under Chemistry with Computers.
5. Make sure that your units on the x-axis are appropriate given the concentration of your copper
solutions.
6. Calibrate your colorimeter by pressing the calibrate button on the colorimeter with the absorbance
set at 645 nm. The calibration solution should be your solvent, HNO3. As HNO3 has no color, the
absorbance reading should be zero with this solution. Dislodge any bubbles in the solution and cap
the cuvette. Wipe the outside with a kimwipe and place it in the colorimeter.
7. You are now ready to collect absorbance data for the four standard solutions. You must use only
one cuvette! Click
. Use the HNO3 solution (the same one used to calibrate the
colorimeter, as your first solution). Dislodge any bubbles in the solution and cap the cuvette. Wipe
the outside with a kimwipe and place it in the colorimeter. After closing the lid, wait for the
absorbance value displayed on the monitor to stabilize. Then click
, type in the concentration
in the edit box, and press the ENTER key. The data pair you just collected should now be plotted on
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Chemistry 153
Clark College
the graph. Then move on to the most dilute solution, rinse the cuvette twice with ~1-mL amounts of
the solution and then fill it 80% full. Measure the absorbance of each of these solutions at 635 nm.
8. You should also record the absorbencies of all solutions in your notebook.
9. Once you have generated your calibration curve, stop the data collection and insert the best-fit line.
Print out your calibration graph with the regression box showing the best-fit line.
10. Report the absorptivity value () of the copper complex, with the correct units!
11. You will now insert your copper solution samples into the colorimeter and record the absorbance of
each. Using the equation of the best-fit line and the absorbance, you will calculate the concentration
of the copper ion in each of your solutions.
Part 5: Putting it all together
Part of your writing assignment for this lab will be to create your OWN report sheet(s) which contains
the important results obtained in this lab. Model your report sheet off previous assignments provided
for previous labs. Remember that you will need to include the results in your lab notebook as well.
Use your vast knowledge of stoichiometry to determine the exact formula for the copper complex.
Remember- a formula is a ratio of moles! You may want to review your stoichiometry and mass
percent notes from CHEM 131!
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Chemistry 153
Chem 135
Clark College
Cu Complex Synthesis and Analysis
PRELAB
Stamp here:
Name: _______________________________________
1. A 0.9863 g sample of the unknown copper complex is dissolved in water and prepared for titration
by the addition of methyl orange indicator. The sample is titrated with 0.485 M HCl, and requires
24.37 mL to reach the endpoint.
a. How many grams of NH3 were in the sample? Report your answer with ppth precision.
Amount of NH3 =
b. What is the mass percent of ammonia in the sample?
Mass percent NH3 =
2. The concentration of the spectrophotometry stock solution is 0.157 M CuSO4  5H2O.
a. What is the concentration of the Cu+2 ion?
[Cu+2] =
b. If you use 6.00 mL of this solution and dilute it to 10.00 mL, what is the new concentration of
your dilute solution?
[dilute] =
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Summer 2007 Rev NF/AEM Summer07
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Chemistry 153
Clark College
3. Nick El-Amin synthesizes a similar copper complex, and analyzes the complex via similar methods.
The complex has a formula of Cux(NH3)yClz • a H2O. From the various analyses, he determines that
there is 23.12% Cu, 51.35% Cl and 12.40% NH3.
a. What is the mass percent of water in the complex?
Mass percent H2O =
b. Determine the actual formula (the values of x, y, z and a) for the complex.
Formula =
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