0.9 Transition metals  (Page 3/3)

Figure 3. The bubbling apparatus.

• After about 10 minutes of bubbling, turn off the gas flow and immerse the flask in ice water. This will cause further crystallization. After approximately 5 minutes in the ice bath, pour the flask's contents through the filter crucible while it has suction applied using the setup shown below. Record your observations.

Figure 4. Schematic diagram showing sintered-glass filter crucible mounted on suction flask with rubber filter adapter. Clamp the filter flask to a support post to prevent breakage.

• The crystals will remain in the crucible while the solution passes through. Wash your crystals by slowly pouring approximately 5 mL of ethanol over them while suction is applied. Why do we wash with ethanol? Answer on lab report form.
• The next step is recrystallization to obtain a more purified product. Transfer the product crystals to a 250 mL beaker. Add about 80 mL of DI water and stir to dissolve the crystals. Gently heat the beaker over a Bunsen burner (or on high on a hotplate if available), gradually bringing it to a‘slight’boil. Allow the solution to boil gently until its volume has been reduced to about 50 mL. Then let the solution cooled to near room temperature, place the beaker into an ice bath (DO NOT PLACE THE BEAKER IN THE ICE BATH WHILE HOT. IT WILL CRACK AND YOU WILL LOOSE YOUR PRODUCT). Crystal growth should be immediately apparent. After a few minutes in the ice bath, transfer the crystals into the filter crucible. To help with this transfer you may use a rubber policeman on the end of a stirring rod. Remember that your crystals are water-soluble so if you use water in the transfer you will lose the product. Apply suction and rinse the crystals three times with separate 5 mL portions of ethanol. Scrape the crystals onto a watch glass and place in your drawer to dry.

In terms of the materials used, the overall reaction is:

$4\{[\text{Co}(H_{2}O{)}_6]({\text{NO}}_3{)}_2\}+8{\text{NaNO}}_2+{\mathrm{8C}}_2{H}_4({\text{NH}}_2{)}_2+4{\text{HNO}}_3+O_2(g)\to 4\text{trans}-$

$[\text{Co}(\text{en}{)}_2({\text{NO}}_2{)}_2]{\text{NO}}_3+8{\text{NaNO}}_3+\text{26}{H}_{2}O$

However, the actual reaction in solution involves ions and the en species exists partially in the form of

${\text{NH}}_2{\text{CH}}_2{\text{CH}}_2{\text{NH}}_3^{+}$ . From the reaction and quantities used, calculate the theoretical yield and your percentage yield.

Pre-lab: transition metals

(total 10 points)

Hopefully here for the Pre-Lab

Note: In preparing this report you are free to use references and consult with others. However, you may not copy from other students’work (including your laboratory partner) or misrepresent your own data (see honor code).

Name(Print then sign): ___________________________________________________

Lab Day: ___________________Section: ________TA__________________________

• List and draw the common geometries transition metal complexes:
• What are the two types of structural isomers for complex ion salts?
• What are the two types of geometrical isomers for complex ion salts?
• Why do we use Co(II) and then convert to Co(III) when synthesizing $4-\text{trans}[\text{Co}(\text{en}{)}_2({\text{NO}}_2{)}_2]{\text{NO}}_3$ ?
• List two common monodentate ligands and two common bidentate ligands:

Report: transition metals

On my honor, in preparing this report, I know that I am free to use references and consult with others.

Hopefully here for the Report Form

Note: In preparing this report you are free to use references and consult with others. However, you may not copy from other students’work (including your laboratory partner) or misrepresent your own data (see honor code).

Name(Print then sign): ___________________________________________________

Lab Day: ___________________Section: ________TA__________________________

Date ________________ Lab Section___________

Note: In preparing this report you are free to use references and consult with others. However, you may not copy from other students' work (except to compile the group data set) or misrepresent your own data.

1. synthesis

A. Volume of 20% ethylenediamine solution used ______ (r = 0.980 g/mL)

A. observations

• Record your observations after adding the neutralized ethylenediamine solution.

• Record your observations after 10 minutes of moderately vigorous bubbling.
• Record your observations after pouring the flask's contents through the filter crucible while suction is applied.

B. questions

• Why do we wash the crystals with ethanol?

• Give the net chemical equation for the reaction, writing dissociated reactants as ions, the solid product as an undissociated salt, and including all other ionic and neutral species needed to balance charge and mass. Omit any spectator ions that would appear in equally on both sides. 

• Which is the limiting reactant in your experiment?

• Calculate the maximum weight of product you would have obtained if the limiting reactant had reacted fully. This is the theoretical yield. What is your percent yield (the actual yield divided by theoretical yield)?

Theoretical yield _______g Actual yield _______ g

• Is the yield less, same, or more than the theoretical yield? Give reasons for why the actual yield is different theoretical yield.