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3.2 Day 2 Procedure

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  • Day 2 - Synthesis of \([Co(NH_3)_5Cl]Cl_2\)

    Partners should combine their products in order to perform the second synthesis.

    In a 100 mL Erlenmeyer on a stir/hot plate dissolve 2 g of \([Co(NH_3)_4(CO_3)]NO_3\) in 15 mL of water and add ~3 mL of concentrated HCl dropwise until no more CO2 is expelled. Neutralize with concentrated aqueous ammonia (use pH paper to indicate neutrality – to avoid contamination of the cobalt solution, use a glass stir rod to transfer a drop of solution to the paper), and then add 2 mL of concentrated aqueous ammonia. Heat at 75-85°C for 20 minutes.

    Cool the solution to about 50°C. Add 20 mL of concentrated \(HCl\) slowly while gently swirling the mixture. Reheat the mixture for 20 to 30 minutes to 75-85°C; observe the color change. Cool the solution to 5 °C in an ice bath. Collect the fine purple-red crystals of \([Co(NH3)5Cl]Cl2\) by filtration using a medium glass frit and wash twice with 3 mL of ice-cold distilled water, filtering each time. Wash twice with 3 mL of ethanol and filter. Dry in an oven at 100-120°C for one hour, cool, weigh, and calculate the percent yield. Transfer your product to a vial and return the glass frit to the Stockroom. Typical yields vary between 50 and 75%.

    Obtain an IR spectrum of the product and compare it with the spectra obtained above.

    Question: Where are the IR absorptions for bound ammonia?

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